ORCID Profile
0000-0002-7203-5996
Current Organisation
Macquarie University
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Stellar Astronomy and Planetary Systems | Astronomical and Space Sciences | Astronomical and Space Instrumentation
Publisher: EDP Sciences
Date: 2012
Publisher: American Astronomical Society
Date: 03-10-2019
Publisher: Oxford University Press (OUP)
Date: 11-12-2005
Publisher: American Astronomical Society
Date: 20-10-2017
Publisher: American Astronomical Society
Date: 23-12-2014
Publisher: Oxford University Press (OUP)
Date: 21-09-2020
Abstract: We present a map of the total intrinsic reddening across ≃34 deg2 of the Small Magellanic Cloud (SMC) derived using optical (ugriz) and near-infrared (IR YJKs) spectral energy distributions (SEDs) of background galaxies. The reddening map is created using a subs le of 29 274 galaxies with low levels of intrinsic reddening based on the lephare χ2 minimization SED-fitting routine. We find statistically significant enhanced levels of reddening associated with the main body of the SMC compared with regions in the outskirts [ΔE(B − V) ≃ 0.3 mag]. A comparison with literature reddening maps of the SMC shows that, after correcting for differences in the volume of the SMC s led, there is good agreement between our results and maps created using young stars. In contrast, we find significant discrepancies between our results and maps created using old stars or based on longer wavelength far-IR dust emission that could stem from biased s les in the former and uncertainties in the far-IR emissivity and the optical properties of the dust grains in the latter. This study represents one of the first large-scale categorizations of extragalactic sources behind the SMC and as such we provide the lephare outputs for our full s le of ∼500 000 sources.
Publisher: Springer Berlin Heidelberg
Date: 19-07-2011
Publisher: Cambridge University Press (CUP)
Date: 12-2006
Publisher: EDP Sciences
Date: 2002
Publisher: Springer Science and Business Media LLC
Date: 10-10-2009
Publisher: Cambridge University Press (CUP)
Date: 2005
DOI: 10.1017/S1539299600015987
Abstract: Star cluster formation is a major mode of star formation in the extreme conditions of interacting galaxies and violent starbursts. Young clusters are observed to form in a variety of such galaxies, a substantial number resembling the progenitors of globular clusters in mass and size, but with significantly enhanced metallicity. From studies of the metal-poor and metal-rich star cluster populations of galaxies, we can therefore learn about the violent star formation history of these galaxies, and eventually about galaxy formation and evolution. We present a new set of evolutionary synthesis models of our GALEV code, with special emphasis on the gaseous emission of presently forming star clusters, and a new tool to compare extensive model grids with multi-color broad-band observations to determine in idual cluster masses, metallicities, ages and extinction values independently. First results for young star clusters in the dwarf starburst galaxy NGC 1569 are presented. The mass distributions determined for the young clusters give valuable input to dynamical star cluster system evolution models, regarding survival and destruction of clusters. We plan to investigate an age sequence of galaxy mergers to see dynamical destruction effects in process.
Publisher: American Astronomical Society
Date: 14-12-2005
DOI: 10.1086/499776
Publisher: EDP Sciences
Date: 23-03-2016
Publisher: Oxford University Press (OUP)
Date: 03-2002
Publisher: EDP Sciences
Date: 05-1996
DOI: 10.1051/AAS:1996151
Publisher: American Astronomical Society
Date: 08-05-2015
Publisher: American Astronomical Society
Date: 27-11-2018
Publisher: Oxford University Press (OUP)
Date: 21-08-2023
Abstract: In our recent catalogue of BY Draconis (BY Dra) variables based on Zwicky Transient Facility data, we found traces of a period gap in the period–colour diagram. We combined our BY Dra database with catalogues from the Kepler and K2 surveys, revealing a prominent period gap. Here, we use this combined ZTF–Kepler–K2 data set to investigate the origin of the period gap observed for BY Dra stars using chromospheric activity indices. We use low- and medium-resolution spectra from the LAMOST Data Release 7 to derive magnetic activity indices for the Ca ii H and K and Hα emission lines. We find a strong dependence of chromospheric activity on both stellar mass and rotation period. For partially convective K–M-type stars, the activity decreases steeply up to an age of ∼700–1000 Myr, subsequently evolving to the type of low-level saturation associated with spin-down stallation. In contrast, F–G-type stars with thinner convective envelopes exhibit constant activity with increasing age. We suspect that the observed steep decrease for partially convective stars is driven by core–envelope coupling. This mechanism reduces differential rotation at the core–envelope transition, hence leading to decreased magnetic activity. Moreover, we derive activity indices for previously known star clusters and find similar trends as regards their activity levels as a function of age. In particular, very low-level activity is observed around the location of the period gap. Therefore, we conclude that the period gap, defined by the non-detection of variable sources, is driven by a minimum in chromospheric activity.
Publisher: American Astronomical Society
Date: 14-12-2015
Publisher: Cambridge University Press (CUP)
Date: 14-05-2010
DOI: 10.1017/S174392131000517X
Abstract: The business session for Commission 37 was held on 11 August 2009 at the IAU General Assembly in Rio de Janeiro. The meeting was attended by about a dozen members of our Comission, including President Elmegreen, VP Carraro and several committee members. We introduced ourselves and then went through a powerpoint presentation first prepared by outgoing President Hatzidimitriou and revised by incoming President Elmegreen. The contents of the powerpoint presentation are given in this summary.
Publisher: IOP Publishing
Date: 27-05-2009
Publisher: Cambridge University Press (CUP)
Date: 07-2008
DOI: 10.1017/S1743921308028639
Abstract: The evolution of star clusters in the Magellanic Clouds has been the subject of significant recent controversy, particularly regarding the importance and length of the earliest, largely mass-independent disruption phase (referred to as “infant mortality”). Here, we take a fresh approach to the problem, using a large, independent, and homogeneous data set of UBVR imaging observations, from which we obtain the cluster age and mass distributions in both the Large and Small Magellanic Clouds (LMC, SMC) in a self-consistent manner. We conclude that the (optically selected) SMC star cluster population has undergone at most ~30% (1σ) infant mortality between the age range from about 3–10 Myr, to that of approximately 40–160 Myr. We rule out a 90% cluster mortality rate per decade of age (for the full age range up to 10 9 yr) at a 6σ level. Using a simple approach, we derive a “characteristic” cluster disruption time-scale for the cluster population in the LMC that implies that we are observing the initial cluster mass function (CMF). Preliminary results suggest that the LMC cluster population may be affected by % infant mortality.
Publisher: Springer-Verlag
Date: 2003
DOI: 10.1007/10857603_10
Publisher: Elsevier BV
Date: 07-2010
Publisher: American Astronomical Society
Date: 26-03-2014
Publisher: Springer Netherlands
Date: 2007
Publisher: Springer Science and Business Media LLC
Date: 04-02-2019
Publisher: Cambridge University Press (CUP)
Date: 08-2015
DOI: 10.1017/S174392131600096X
Abstract: It is widely accepted that stars do not form in isolation but result from the fragmentation of molecular clouds, which in turn leads to star cluster formation. Over time, clusters dissolve or are destroyed by interactions with molecular clouds or tidal stripping, and their members become part of the general field population. Star clusters are thus among the basic building blocks of galaxies. In turn, star cluster populations, from young associations and open clusters to old globulars, are powerful tracers of the formation, assembly, and evolutionary history of their parent galaxies. Although their importance (e.g., in mapping out the Milky Way) had been recognised for decades, major progress in this area has only become possible in recent years, both for Galactic and extragalactic cluster populations. Star clusters are the observational foundation for stellar astrophysics and evolution, provide essential tracers of galactic structure, and are unique stellar dynamical environments. Star formation, stellar structure, stellar evolution, and stellar nucleosynthesis continue to benefit and improve tremendously from the study of these systems. Additionally, fundamental quantities such as the initial mass function can be successfully derived from modelling either the Hertzsprung-Russell diagrams or the integrated velocity structures of, respectively, resolved and unresolved clusters and cluster populations. Star cluster studies thus span the fields of Galactic and extragalactic astrophysics, while heavily affecting our detailed understanding of the process of star formation in dense environments. This report highlights science results of the last decade in the major fields covered by IAU Commission 37: Star clusters and associations. Instead of focusing on the business meeting - the out-going president presentation can be found here: carraro/splinter2015.pdf - this legacy report contains highlights of the most important scientific achievements in the Commission science area, compiled by 5 well expert members.
Publisher: IOP Publishing
Date: 2015
Publisher: American Astronomical Society
Date: 10-11-2021
Publisher: American Astronomical Society
Date: 27-07-2023
Publisher: Oxford University Press (OUP)
Date: 04-2021
Abstract: The conventional picture of coeval, chemically homogeneous, populous star clusters – known as ‘simple’ stellar populations (SSPs) – is a view of the past. Photometric and spectroscopic studies reveal that almost all ancient globular clusters in the Milky Way and our neighbouring galaxies exhibit star-to-star light-element abundance variations, typically known as ‘multiple populations’ (MPs). Here, we analyse photometric Hubble Space Telescope observations of three young (& -Gyr old) Large and Small Magellanic Cloud clusters, NGC 411, NGC 1718, and NGC 2213. We measure the widths of their red giant branches (RGBs). For NGC 411, we also use a pseudo-colour–magnitude diagram (pseudo-CMD) to assess its RGB for evidence of MPs. We compare the morphologies of the clusters’ RGBs with artificially generated SSPs. We conclude that their RGBs do not show evidence of significant broadening beyond intrinsic photometric scatter, suggesting an absence of significant chemical abundance variations in our s le clusters. Specifically, for NGC 411, NGC 1718, and NGC 2213 we derive maximum helium-abundance variations of δY = 0.003 ± 0.001(Y = 0.300), 0.002 ± 0.001(Y = 0.350), and 0.004 ± 0.002(Y = 0.300), respectively. We determined an upper limit to the NGC 411 nitrogen-abundance variation of Δ[N/Fe] = 0.3 dex the available data for our other clusters do not allow us to determine useful upper limits. It thus appears that the transition from SSPs to MPs occurs at an age of ∼2 Gyr, implying that age might play an important role in this transition. This raises the question as to whether this is indeed a fundamental minimum age limit for the formation of MPs.
Publisher: Oxford University Press (OUP)
Date: 20-10-2021
Abstract: Recent observational studies identified a foreground stellar sub-structure traced by red clump (RC) stars (∼12 kpc in front of the main body) in the eastern regions of the Small Magellanic Cloud (SMC) and suggested that it formed during the formation of the Magellanic Bridge (MB), due to the tidal interaction of the Magellanic Clouds. Previous studies investigated this feature only up to 4${_{.}^{\\circ}}$0 from the centre of the SMC due to the limited spatial coverage of the data and hence could not find a physical connection with the MB. To determine the spatial extent and properties of this foreground population, we analysed data from the Gaia Data Release 2 (DR2) of a ∼314 deg2 region centred on the SMC, which cover the entire SMC and a significant portion of the MB. We find that the foreground population is present only between 2${_{.}^{\\circ}}$5 to ∼5°–6° from the centre of the SMC in the eastern regions, towards the MB and hence does not fully overlap with the MB in the plane of the sky. The foreground stellar population is found to be kinematically distinct from the stellar population of the main body with ∼35 km s−1 slower tangential velocity and moving to the north-west relative to the main body. Though the observed properties are not fully consistent with the simulations, a comparison indicates that the foreground stellar structure is most likely a tidally stripped counterpart of the gaseous MB and might have formed from the inner disc (dominated by stars) of the SMC. A chemical and 3D kinematic study of the RC stars along with improved simulations, including both tidal and hydro-dynamical effects, are required to understand the offset between the foreground structure and MB.
Publisher: Oxford University Press (OUP)
Date: 11-2013
Publisher: American Astronomical Society
Date: 02-2000
DOI: 10.1086/301235
Publisher: Oxford University Press (OUP)
Date: 05-06-2018
Abstract: We study the effects of bulge elongation on the star formation activity in the centres of spiral galaxies using the data from the Sloan Digital Sky Survey Data Release 7. We construct a volume-limited s le of face-on spiral galaxies with Mr & −19.5 mag at 0.02 ≤ $z$ & 0.055 by excluding barred galaxies, where the aperture of the SDSS spectroscopic fibre covers the bulges of the galaxies. We adopt the ellipticity of bulges measured by Simard et al., who performed two-dimensional bulge + disc decompositions using the SDSS images of galaxies, and identify nuclear starbursts using the fibre specific star formation rates derived from the SDSS spectra. We find a statistically significant correlation between bulge elongation and nuclear starbursts in the sense that the fraction of nuclear starbursts increases with bulge elongation. This correlation is more prominent for fainter and redder galaxies, which exhibit higher ratios of elongated bulges. We find no significant environmental dependence of the correlation between bulge elongation and nuclear starbursts. These results suggest that non-axisymmetric bulges can efficiently feed the gas into the centre of galaxies to trigger nuclear starburst activity.
Publisher: American Astronomical Society
Date: 02-2023
Abstract: RR Lyrae variables are excellent Population II distance indicators thanks to their well-defined period–luminosity relations (PLRs) at infrared wavelengths. We present results of near-infrared (NIR) monitoring of Galactic globular clusters to empirically quantify the metallicity dependence of NIR PLRs for RR Lyrae variables. Our s le includes homogeneous, accurate, and precise photometric data for 964 RR Lyrae variables in 11 globular clusters covering a large metallicity range (Δ[Fe/H] ∼ 2 dex). We derive JHK s -band period–luminosity–metallicity (PLZ) and period–Wesenheit–metallicity (PWZ) relations anchored using 346 Milky Way field RR Lyrae stars with Gaia parallaxes, and simultaneously solved for independent distances to globular clusters. We find a significant metallicity dependence of ∼0.2 mag dex −1 in the JHK s -band PLZ and PWZ relations for RR Lyrae stars independent of the adopted metallicity scale. The metallicity coefficients and the zero-points of the empirical PLZ and PWZ relations are in excellent agreement with the predictions from the horizontal branch evolution and pulsation models. Furthermore, RR Lyrae–based distances to our s le of globular clusters are also statistically consistent with other independent measurements in the literature. Our recommended empirical JHK s -band PLZ relations for RR Lyrae stars with periods of fundamental mode pulsation ( P f ) are: M J = − 0.44 ( ± 0.03 ) − 1.83 ( ± 0.02 ) log ( P f ) + 0.20 ( ± 0.02 ) [ Fe / H ] ( σ = 0.05 mag ) M H = − 0.74 ( ± 0.02 ) − 2.29 ( ± 0.02 ) log ( P f ) + 0.19 ( ± 0.01 ) [ Fe / H ] ( σ = 0.05 mag ) M K s = − 0.80 ( ± 0.02 ) − 2.37 ( ± 0.02 ) log ( P f ) + 0.18 ( ± 0.01 ) [ Fe / H ] ( σ = 0.05 mag ) .
Publisher: American Astronomical Society
Date: 21-12-2015
Publisher: Oxford University Press (OUP)
Date: 21-09-2016
Publisher: Springer Science and Business Media LLC
Date: 05-2018
Publisher: Oxford University Press (OUP)
Date: 23-08-2019
Abstract: We present a method to map the total intrinsic reddening of a foreground extinguishing medium via the analysis of spectral energy distributions (SEDs) of background galaxies. In this pilot study, we implement this technique in two distinct regions of the Small Magellanic Cloud (SMC) – the bar and the southern outskirts – using a combination of optical and near-infrared ugrizYJKs broad-band imaging. We adopt the lephare χ2-minimization SED-fitting routine and various s les of galaxies and/or quasi-stellar objects to investigate the intrinsic reddening. We find that only when we construct reddening maps using objects classified as galaxies with low levels of intrinsic reddening (i.e. ellipticals/lenticulars and early-type spirals), the resultant maps are consistent with previous literature determinations, i.e. the intrinsic reddening of the SMC bar is higher than that in the outer environs. We employ two sets of galaxy templates – one theoretical and one empirical – to test for template dependences in the resulting reddening maps and find that the theoretical templates imply systematically higher reddening values by up to 0.20 mag in E(B − V). A comparison with previous reddening maps, based on the stellar components of the SMC, typically shows reasonable agreement. There is, however, significant variation amongst the literature reddening maps as to the level of intrinsic reddening associated with the bar. Thus, it is difficult to unambiguously state that instances of significant discrepancies are the result of appreciable levels of dust not accounted for in some literature reddening maps or whether they reflect issues with our adopted methodology.
Publisher: EDP Sciences
Date: 11-09-2008
Publisher: American Astronomical Society
Date: 06-06-2017
Publisher: Springer Science and Business Media LLC
Date: 24-12-2009
Publisher: American Astronomical Society
Date: 07-12-2007
Publisher: Springer Berlin Heidelberg
Date: 18-11-2004
DOI: 10.1007/10857598_42
Publisher: Oxford University Press (OUP)
Date: 12-2006
Publisher: American Astronomical Society
Date: 02-06-2016
Publisher: EDP Sciences
Date: 07-2022
DOI: 10.1051/0004-6361/202142148
Abstract: Context. The Large Magellanic Cloud (LMC) is the most luminous satellite galaxy of the Milky Way and, owing to its companion, the Small Magellanic Cloud (SMC), represents an excellent laboratory to study the interaction of dwarf galaxies. Aims. The aim of this study is to investigate the kinematics of the outer regions of the LMC by using stellar proper motions to understand the impact of interactions, for ex le with the SMC about 250 Myr ago. Methods. We calculate proper motions using multi-epoch K s -band images from the VISTA survey of the Magellanic Cloud system (VMC). Observations span a time baseline of 2−5 yr. We combine the VMC data with data from the Gaia Early Data Release 3 and introduce a new method to distinguish between Magellanic and Milky Way stars based on a machine learning algorithm. This new technique enables a larger and cleaner s le selection of fainter sources as it reaches below the red clump of the LMC. Results. We investigate the impact of the SMC on the rotational field of the LMC and find hints of stripped SMC debris. The south-eastern region of the LMC shows a slow rotational speed compared to the overall rotation. N -body simulations suggest that this could be caused by a fraction of stripped SMC stars located in that particular region that move opposite to the expected rotation.
Publisher: American Astronomical Society
Date: 07-2004
DOI: 10.1086/421363
Publisher: Oxford University Press (OUP)
Date: 22-08-2020
Abstract: Reliable models of the thermally pulsing asymptotic giant branch (TP-AGB) phase are of critical importance across astrophysics, including our interpretation of the spectral energy distribution of galaxies, cosmic dust production, and enrichment of the interstellar medium. With the aim of improving sets of stellar isochrones that include a detailed description of the TP-AGB phase, we extend our recent calibration of the AGB population in the Small Magellanic Cloud (SMC) to the more metal-rich Large Magellanic Cloud (LMC). We model the LMC stellar populations with the trilegal code, using the spatially resolved star formation history derived from the VISTA survey. We characterize the efficiency of the third dredge-up by matching the star counts and the Ks-band luminosity functions of the AGB stars identified in the LMC. In line with previous findings, we confirm that, compared to the SMC, the third dredge-up in AGB stars of the LMC is somewhat less efficient, as a consequence of the higher metallicity. The predicted range of initial mass of C-rich stars is between Mi ≈ 1.7 and 3 M⊙ at Zi = 0.008. We show how the inclusion of new opacity data in the carbon star spectra will improve the performance of our models. We discuss the predicted lifetimes, integrated luminosities, and mass-loss rate distributions of the calibrated models. The results of our calibration are included in updated stellar isochrones publicly available.
Publisher: American Astronomical Society
Date: 03-05-2018
Publisher: Oxford University Press (OUP)
Date: 21-05-2009
Publisher: Springer Science and Business Media LLC
Date: 07-09-2016
DOI: 10.1038/NATURE19336
Publisher: American Astronomical Society
Date: 08-04-2011
Publisher: EDP Sciences
Date: 08-2019
DOI: 10.1051/0004-6361/201834403
Abstract: Context . The formation of globular clusters remains an open debate. Dwarf starburst galaxies are efficient at forming young massive clusters with similar masses as globular clusters and may hold the key to understanding their formation. Aims . We study star cluster formation in a tidal debris, including the vicinity of three tidal dwarf galaxies, in a massive gas-dominated collisional ring around NGC 5291. These dwarfs have physical parameters that differ significantly from local starbursting dwarfs. They are gas rich, highly turbulent, their gas metallicity is already enriched up to half solar values, and they are expected to be free of dark matter. The aim is to study massive star cluster formation in this as yet unexplored type of environment. Methods . We used imaging from the Hubble Space Telescope using broadband filters that cover the wavelength range from the near-ultraviolet to the near-infrared. We determined the masses and ages of the cluster candidates by using the spectral energy distribution-fitting code CIGALE. We considered age-extinction degeneracy effects on the estimation of the physical parameters. Results . We find that the tidal dwarf galaxies in the ring of NGC 5291 are forming star clusters with an average efficiency of ∼40%, which is similar to blue compact dwarf galaxies. We also find massive star clusters for which the photometry suggests that they were formed at the very birth of the tidal dwarf galaxies. These clusters have survived for several hundred million years. Therefore our study shows that extended tidal dwarf galaxies and compact clusters may be formed simultaneously. In the specific case observed here, the young star clusters are not massive enough to survive for a Hubble time. However, it may be speculated that similar objects at higher redshift, with a higher star formation rate, might form some of the long-lived globular clusters.
Publisher: American Astronomical Society
Date: 06-2018
Publisher: American Astronomical Society
Date: 20-12-2019
Publisher: Wiley
Date: 02-09-2011
Publisher: Oxford University Press (OUP)
Date: 03-2002
Publisher: American Astronomical Society
Date: 06-12-2016
Publisher: EDP Sciences
Date: 04-10-2006
Publisher: American Astronomical Society
Date: 28-07-2017
Publisher: IOP Publishing
Date: 03-01-2018
Publisher: Cambridge University Press (CUP)
Date: 08-2015
DOI: 10.1017/S1743921316003471
Abstract: At the 2012 General Assembly of the International Astronomical Union (IAU), the Office of Astronomy for Development announced a number of exciting new partnerships to assist with the IAU's decadal strategic plan (2010--2020). These landmark decisions included establishing a new coordinating centre that aims at using astronomy as a tool for development in East Asia. The agreement covers two important functions. One is known as a Regional Node, which entails the coordination of astronomy-for-development activities in countries within the general geographical region of East Asia. The other is known as a Language Expertise Centre which deals with all aspects relating to (mainly) the Chinese language and culture. The impact of the latter may obviously spread well beyond the geographical region to other parts of the world. Here we provide an update of the achievements and aims of the East Asian Office of Astronomy for Development.
Publisher: American Astronomical Society
Date: 27-04-2020
Abstract: We consider the body of published distance moduli to the Fornax and Coma galaxy clusters, with specific emphasis on the period since 1990. We have carefully homogenized our final catalogs of distance moduli onto the distance scale established in the previous papers in this series. We assessed systematic differences associated with the use of specific tracers and consequently discarded results based on application of the Tully–Fisher relation and of globular cluster and planetary nebula luminosity functions. We recommend “best” weighted relative distance moduli for the Fornax and Coma clusters with respect to the Virgo cluster benchmark of mag and mag. The set of weighted mean distance moduli (distances) we derived as most representative of the clusters’ distances is m − M 0 F o r n a x = 31.41 ± 0.15 m a g ( D = 19.1 − 1.2 + 1.4 M p c ) a n d = 31.21 ± 0.28 m a g ( D = 17.5 − 2.2 + 2.4 M p c ) , m − M 0 C o m a = 34.99 ± 0.38 m a g ( D = 99.5 − 15.9 + 19.0 M p c ) a n d = 34.78 ± 0.27 m a g ( D = 90.4 − 10.6 + 11.9 M p c ) , where the first distance modulus for each cluster is the result of our analysis of the direct, absolute distance moduli, while the second modulus is based on distance moduli relative to the Virgo cluster. While the absolute and relative distance moduli for both clusters are mutually consistent within the uncertainties, the relative distance moduli yield shorter absolute distances by ∼1 σ . It is unclear what may have caused this small difference for both clusters lingering uncertainties in the underlying absolute distance scale appear to have given rise to a systematic uncertainty of the order of 0.20 mag.
Publisher: Oxford University Press (OUP)
Date: 08-2001
Publisher: IOP Publishing
Date: 04-2007
Publisher: Wiley
Date: 02-09-2011
Publisher: Oxford University Press (OUP)
Date: 10-11-2016
Publisher: Cambridge University Press (CUP)
Date: 2005
DOI: 10.1017/S1539299600015616
Abstract: We present a new set of evolutionary synthesis models of our GALEV code, specifically developed to include the gaseous emission of presently forming star clusters, in combination with an advanced tool to compare large model grids with multi-color broad-band observations of YSC systems. Tests and first applications are presented.
Publisher: Oxford University Press (OUP)
Date: 13-04-2006
Publisher: EDP Sciences
Date: 25-04-2006
Publisher: Cambridge University Press (CUP)
Date: 2005
DOI: 10.1017/S1539299600015975
Abstract: The production of “super star clusters” (SSCs luminous, compact star clusters) seems to be a hallmark of intense star formation, particularly in interacting and star-burst galaxies. Their sizes, luminosities, and mass estimates are entirely consistent with what is expected for young Milky Way-type globular clusters (GCs). SSCs are important because of what they can tell us about GC formation and evolution (e.g., initial characteristics and early survival rates). They are also of prime importance as probes of the formation and (chemical) evolution of their host galaxies, and of the initial mass function in the extreme environments required for cluster formation. Recent evidence lends support to the scenario that Milky Way-type GCs (although more metal rich), which were once thought to be the oldest building blocks of galaxies, are still forming today.
Publisher: Oxford University Press (OUP)
Date: 04-03-2020
Abstract: Studies of young stellar objects (YSOs) in the Galaxy have found that a significant fraction exhibits photometric variability. However, no systematic investigation has been conducted on the variability of extragalactic YSOs. Here we present the first variability study of massive YSOs in an $\\sim 1.5\\, \\mathrm{deg^2}$ region of the Large Magellanic Cloud (LMC). The aim is to investigate whether the different environmental conditions in the metal-poor LMC ($\\sim 0.4\\!-\\!0.5\\, \\mathrm{Z_{\\odot }}$) have an impact on the variability characteristics. Multi-epoch near-infrared (NIR) photometry was obtained from the VISTA Survey of the Magellanic Clouds (VMC) and our own monitoring c aign using the VISTA telescope. By applying a reduced χ2-analysis, stellar variability was identified. We found 3062 candidate variable stars from a population of 362 425 stars detected. Based on several Spitzer studies, we compiled a s le of high-reliability massive YSOs: a total of 173 massive YSOs have NIR counterparts (down to $K_s\\sim 18.5\\,$mag) in the VMC catalogue, of which 39 display significant (& σ) variability. They have been classified as eruptive, fader, dipper, short-term variable, and long-period variable YSOs based mostly on the appearance of their Ks-band light curves. The majority of YSOs are aperiodic only five YSOs exhibit periodic light curves. The observed litudes are comparable or smaller than those for Galactic YSOs (only two Magellanic YSOs exhibit $\\Delta K_s\\gt 1\\,$mag), not what would have been expected from the typically larger mass accretion rates observed in the Magellanic Clouds.
Publisher: Oxford University Press (OUP)
Date: 21-07-2006
Publisher: American Astronomical Society
Date: 25-09-2012
Publisher: Oxford University Press (OUP)
Date: 06-12-2019
Abstract: We present a CO(3–2) survey of selected regions in the M31 disc as part of the JCMT large programme, HARP and SCUBA-2 High-Resolution Terahertz Andromeda Galaxy Survey (HASHTAG). The 12 CO(3–2) fields in this survey cover a total area of 60 arcmin2, spanning a deprojected radial range of 2–14 kpc across the M31 disc. Combining these observations with existing IRAM 30 m CO(1–0) observations and JCMT CO(3–2) maps of the nuclear region of M31, as well as dust temperature and star formation rate surface density maps, we are able to explore the radial distribution of the CO(3–2)/CO(1–0) integrated intensity ratio (R31) and its relationship with dust temperature and star formation. We find that the value of R31 between 2 and 9 kpc galactocentric radius is 0.14, significantly lower than what is seen in the nuclear ring at 1 kpc (R31 ∼ 0.8), only to rise again to 0.27 for the fields centred on the 10 kpc star forming ring. We also found that R31 is positively correlated with dust temperature, with Spearman’s rank correlation coefficient ρ = 0.55. The correlation between star formation rate surface density and CO(3–2) intensity is much stronger than with CO(1–0), with ρ = 0.54 compared to –0.05, suggesting that the CO(3–2) line traces warmer and denser star forming gas better. We also find that R31 correlates well with star formation rate surface density, with ρ = 0.69.
Publisher: Cambridge University Press (CUP)
Date: 2005
DOI: 10.1017/S1539299600017354
Abstract: Star cluster formation is a major mode of star formation in the extreme conditions of interacting galaxies and violent star bursts. These newly-formed clusters are built from recycled gas, pre-enriched to various levels within the interacting galaxies. Hence, star clusters of different ages represent a fossil record of the chemical enrichment history of their host galaxy, as well as of the host galaxy’s violent star formation history. We present a new set of evolutionary synthesis models of our GALEV code, specifically developed to include the gaseous emission of presently forming star clusters, and a new tool to analyze multi-color observations with our models. First results for newly-born clusters in the dwarf star-burst galaxy NGC 1569 are presented.
Publisher: NAS RA Byurakan Astrophysical Observatory after V. A. Ambartsumian
Date: 2018
DOI: 10.52526/25792776-2018.2.2-193
Abstract: Although the formation of blue straggler stars (BSSs) is routinely attributed to stellar interactions in binary systems, the relative importance of the direct collision and slow(er) stellar coalescence formation channels is still poorly understood. We selected a s le of 24 Magellanic Cloud star clusters for which multi-passband Hubble Space Telescope images are available to address this outstanding question. We compiled a BSS database, containing both traditional and evolved BSSs. We found a robust correlation between the number of BSSs in a cluster’s core and its core mass, NBSS,core ∝ M0.51±0.07 core, which supports the notion that BSS formation is linked to a population’s binary fraction. At low stellar collision rates, the mass-normalised number of BSSs does not appear to depend on the collision rate, which implies that the coalescence-driven BSS formation channel dominates. Comparison with simulations suggests that stellar collisions contribute less than 20% to the total number of BSSs formed.
Publisher: Springer Netherlands
Date: 2019
Publisher: Oxford University Press (OUP)
Date: 17-08-2010
Publisher: Cambridge University Press (CUP)
Date: 08-2015
DOI: 10.1017/S1743921315009096
Abstract: Characterization of the binary fractions in star clusters is of fundamental importance for many fields in astrophysics. Observations indicate that the majority of stars are found in binary systems, while most stars with masses greater than 0.5 M ⊙ are formed in star clusters. In addition, since binaries are on average more massive than single stars, in resolved star clusters these systems are thought to be good tracers of (dynamical) mass segregation. Over time, dynamical evolution through two-body relaxation will cause the most massive objects to migrate to the cluster center, while the relatively lower-mass objects remain in or migrate to orbits at greater radii. This process will globally dominate a cluster’s stellar distribution. However, close encounters involving binary systems may disrupt ‘soft’ binaries. This process will occur more frequently in a cluster’s central, dense region than in its periphery, which may mask the effects of mass segregation. Using high resolution Hubble Space Telescope observations, combined with sophisticated N -body simulations, we investigate the radial distributions of the main-sequence binary fractions in massive young Large Magellanic Cloud star clusters. We show that binary disruption may play an important role on very short timescales, depending on the environmental conditions in the cluster cores. This may lead to radial binary fractions that initially decline in the cluster centers, which is contrary to the effects expected from dynamical mass segregation.
Publisher: EDP Sciences
Date: 04-2023
DOI: 10.1051/0004-6361/202244798
Abstract: In the past few years, we have undertaken an extensive investigation of star clusters and their stellar populations in the Large and Small Magellanic Clouds (LMC and SMC) based on archival images collected with the Hubble Space Telescope. We present photometry and astrometry of stars in 101 fields observed with the Wide Field Channel of the Advanced Camera for Surveys and the Ultraviolet and Visual Channel and the Near-Infrared Channel of Wide Field Camera 3. These fields comprise 113 star clusters. We provide differential-reddening maps for those clusters with significant reddening variations across the field of view. We illustrate various scientific outcomes that arise from the early inspection of the photometric catalogs. In particular, we provide new insights into the extended main-sequence turnoff (eMSTO) phenomenon: (i) We detected eMSTOs in two clusters, KMHK 361 and NGC 265, which had no previous evidence of multiple populations. This finding corroborates the conclusion that the eMSTO is a widespread phenomenon among clusters younger than ∼2 Gyr. (ii) The homogeneous color-magnitude diagrams (CMDs) of 19 LMC clusters reveal that the distribution of stars along the eMSTO depends on cluster age. (iii) We discovered a new feature along the eMSTO of NGC 1783, which consists of a distinct group of stars on the red side of the eMSTO in CMDs composed of UV filters. Furthermore, we derived the proper motions of stars in the fields of view of clusters with multi-epoch images. Proper motions allowed us to separate the bulk of bright field stars from cluster members and investigate the internal kinematics of stellar populations in various LMC and SMC fields. As an ex le, we analyze the field around NGC 346 to disentangle the motions of its stellar populations, including NGC 364 and BS 90, young and pre-main-sequence stars in the star-forming region associated with NGC 346, and young and old field stellar populations of the SMC. Based on these results and the fields around five additional clusters, we find that young SMC stars exhibit elongated proper-motion distributions that point toward the LMC, thus providing new evidence for a kinematic connection between the LMC and SMC.
Publisher: EDP Sciences
Date: 04-02-2011
Publisher: EDP Sciences
Date: 15-05-2008
Publisher: Oxford University Press (OUP)
Date: 16-10-2014
Publisher: American Astronomical Society
Date: 10-10-2006
DOI: 10.1086/507175
Publisher: American Astronomical Society
Date: 31-10-2019
Publisher: Oxford University Press (OUP)
Date: 29-01-2021
Abstract: We used data from the near-infrared Visible and Infrared Telescope for Astronomy (VISTA) survey of the Magellanic Cloud system (VMC) to measure proper motions (PMs) of stars within the Small Magellanic Cloud (SMC). The data analysed in this study comprise 26 VMC tiles, covering a total contiguous area on the sky of ∼40 deg2. Using multi-epoch observations in the Ks band over time baselines between 13 and 38 months, we calculated absolute PMs with respect to ∼130 000 background galaxies. We selected a s le of ∼2160 000 likely SMC member stars to model the centre-of-mass motion of the galaxy. The results found for three different choices of the SMC centre are in good agreement with recent space-based measurements. Using the systemic motion of the SMC, we constructed spatially resolved residual PM maps and analysed for the first time the internal kinematics of the intermediate-age/old and young stellar populations separately. We found outward motions that point either towards a stretching of the galaxy or stripping of its outer regions. Stellar motions towards the North might be related to the ‘Counter Bridge’ behind the SMC. The young populations show larger PMs in the region of the SMC Wing, towards the young Magellanic Bridge. In the older populations, we further detected a coordinated motion of stars away from the SMC in the direction of the Old Bridge as well as a stream towards the SMC.
Publisher: Oxford University Press (OUP)
Date: 07-2011
Publisher: Oxford University Press (OUP)
Date: 30-03-2016
DOI: 10.1093/MNRAS/STW716
Publisher: IOP Publishing
Date: 06-2016
Publisher: Wiley
Date: 25-11-2008
Abstract: The diagnostic age versus mass‐to‐light ratio diagram is often used in attempts to constrain the shape of the stellar initial mass function, and the stability and the potential longevity of extragalactic young to intermediate‐age massive star clusters. Here, we explore the pitfalls associated with this approach and its potential for use with Galactic open clusters. We conclude that for an open cluster to survive for any significant fraction of a Hubble time (in the absence of substantial external perturbations), it is a necessary but not a sufficient condition to be located close to the predicted photometric evolutionary sequences for ‘normal’ simple stellar populations. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Publisher: American Astronomical Society
Date: 29-05-2018
Publisher: Springer Science and Business Media LLC
Date: 2001
Publisher: Springer Netherlands
Date: 2013
Publisher: Oxford University Press (OUP)
Date: 22-06-2016
Publisher: Elsevier BV
Date: 02-2003
Publisher: Oxford University Press (OUP)
Date: 07-2005
Publisher: American Astronomical Society
Date: 25-06-2018
Publisher: Cambridge University Press (CUP)
Date: 12-2012
Publisher: American Astronomical Society
Date: 20-10-2016
Publisher: American Astronomical Society
Date: 12-11-2013
Publisher: Cambridge University Press (CUP)
Date: 04-2008
DOI: 10.1017/S1743921308022618
Abstract: The stellar initial mass function (IMF) is a very important question in modern astrophysics. Globular clusters (GCs) are good s les for studying the IMF, but the Galactic GCs can provide only one time-scale evolutionary stage. The Large Magellanic Cloud (LMC) is an ideal environment for studying the IMF because it contains compact clusters at different evolutionary stages. By studying the IMF at different evolutionary stages, we can see how the mass function evolves with time.
Publisher: Oxford University Press (OUP)
Date: 07-12-2007
Publisher: EDP Sciences
Date: 05-2018
DOI: 10.1051/0004-6361/201833144
Abstract: We present the first spatially resolved map of stellar proper motions within the central (~3.1 × 2.4 kpc) regions of the Small Magellanic Cloud (SMC). The data used for this study encompasses four tiles from the ongoing near-infrared VISTA survey of the Magellanic Clouds system and covers a total contiguous area on the sky of ~6.81 deg 2 . Proper motions have been calculated independently in two dimensions from the spatial offsets in the K s filter over time baselines between 22 and 27 months. The reflex motions of approximately 33 000 background galaxies are used to calibrate the stellar motions to an absolute scale. The resulting catalog is composed of more than 690 000 stars which have been selected based on their position in the ( J − K s , K s ) color-magnitude diagram. For the median absolute proper motion of the SMC, we find ( μ α cos( δ ), μ δ ) = (1.087 ± 0.192 (sys.) ± 0.003 (stat.), −1.187 ± 0.008 (sys.) ± 0.003 (stat.)) mas yr −1 , consistent with previous studies. Mapping the proper motions as a function of position within the SMC reveals a nonuniform velocity pattern indicative of a tidal feature behind the main body of the SMC and a flow of stars in the south-east moving predominantly along the line-of-sight.
Publisher: Springer Science and Business Media LLC
Date: 31-07-2015
DOI: 10.1038/NPHYS3431
Publisher: American Astronomical Society
Date: 20-08-2018
Publisher: Oxford University Press (OUP)
Date: 04-2000
Publisher: American Astronomical Society
Date: 22-11-2013
Publisher: Oxford University Press (OUP)
Date: 04-2015
DOI: 10.1093/MNRAS/STV635
Publisher: Oxford University Press (OUP)
Date: 19-11-2014
Publisher: American Astronomical Society
Date: 20-07-2016
Publisher: Oxford University Press (OUP)
Date: 2004
Publisher: EDP Sciences
Date: 16-04-2008
Publisher: Oxford University Press (OUP)
Date: 06-2020
Abstract: Galaxy interactions distort the distribution of baryonic matter and can affect star formation. The nearby Magellanic Clouds are a prime ex le of an ongoing galaxy interaction process. Here, we use the intermediate-age (∼1–10 Gyr) red clump (RC) stars to map the 3D structure of the Small Magellanic Cloud (SMC) and interpret it within the context of its history of interaction with the Large Magellanic Cloud (LMC) and the Milky Way. RC stars are selected from near-infrared colour–magnitude diagrams based on data from the Visible and Infrared Survey Telescope for Astronomy survey of the Magellanic Clouds. Interstellar reddening is measured and removed, and the corrected brightness is converted to a distance, on a star-by-star basis. A flat plane fitted to the spatial distribution of RC stars has an inclination i = 35°–48° and position angle, PA=170°–186°. However, significant deviations from this plane are seen, especially in the periphery and on the eastern side of the SMC. In the latter part, two distinct populations are present, separated in distance by as much as 10 kpc. Distant RC stars are seen in the north of the SMC, and possibly also in the far west these might be associated with the predicted ‘Counter-Bridge’. We also present a dust reddening map, which shows that dust generally traces stellar mass. The structure of the intermediate-age stellar component of the SMC bears the imprints of strong interaction with the LMC a few Gyr ago, which cannot be purely tidal but must have involved ram pressure stripping.
Publisher: Springer-Verlag
Date: 2003
DOI: 10.1007/10857603_40
Publisher: Oxford University Press (OUP)
Date: 03-09-2019
Abstract: The Magellanic Clouds are nearby dwarf irregular galaxies whose morphologies show different properties when traced by different stellar populations, making them an important laboratory for studying galaxy morphologies. We study the morphology of the Magellanic Clouds using data from the Visible and Infrared Survey Telescope for Astronomy survey of the Magellanic Clouds system. We used about 10 and 2.5 million sources across an area of ∼105 and ∼42 deg2 towards the Large and Small Magellanic Cloud (LMC and SMC), respectively. We estimated median ages of stellar populations occupying different regions of the near-infrared (J − Ks, Ks) colour–magnitude diagram. Morphological maps were produced and detailed features in the central regions were characterized for the first time with bins corresponding to a spatial resolution of 0.13 kpc (LMC) and 0.16 kpc (SMC). In the LMC, we find that main-sequence stars show coherent structures that grow with age and trace the multiple spiral arms of the galaxy, star-forming regions become dimmer as we progress in age, while supergiant stars are centrally concentrated. Intermediate-age stars, despite tracing a regular and symmetrical morphology, show central clumps and hints of spiral arms. In the SMC, young main-sequence stars depict a broken bar. Intermediate-age populations show signatures of elongation towards the Magellanic Bridge that can be attributed to the LMC–SMC interaction ∼200 Myr ago. They also show irregular central features suggesting that the inner SMC has also been influenced by tidal interactions.
Publisher: The Royal Society
Date: 28-02-2010
Abstract: Star clusters and their stellar populations play a significant role in the context of galaxy evolution, across space (from local to high redshift) and time (from currently forming to fossil remnants). We are now within reach of answering a number of fundamental questions that will have a significant impact on our understanding of key open issues in contemporary astrophysics, ranging from the formation, assembly and evolution of galaxies to the details of the star-formation process. Our improved understanding of the physics driving star cluster formation and evolution has led to the emergence of crucial new open questions that will most probably be tackled in a systematic way in the next decade.
Publisher: EDP Sciences
Date: 02-07-2009
Publisher: American Astronomical Society
Date: 03-2022
Abstract: Multiple stellar populations (MPs) representing star-to-star light-element abundance variations are common in nearly all ancient Galactic globular clusters (GCs). Here we provide the strongest evidence yet that the populous, ∼1.7 Gyr old Large Magellanic Cloud cluster NGC 2173 also exhibits light-element abundance variations. Thus, our results suggest that NGC 2173 is the youngest cluster for which MPs have been confirmed to date. Our conclusion is based on the distinct bifurcation at the tip of its red giant branch in high-quality color–magnitude diagrams generated from Hubble Space Telescope imaging observations. Our results are further supported by a detailed analysis of “pseudo- UBI ” maps, which reveal clear evidence of a bimodality in the cluster’s red giant branch color distribution. Young clusters in the Magellanic Clouds can provide critical insights into galaxy evolution histories. Our discovery of MPs in NGC 2173 suggests that ancient Galactic GCs and young massive clusters might share a common formation process.
Publisher: Oxford University Press (OUP)
Date: 11-02-2006
Publisher: EDP Sciences
Date: 2012
Publisher: Springer Science and Business Media LLC
Date: 2003
Publisher: EDP Sciences
Date: 29-01-2019
DOI: 10.1051/0004-6361/201833904
Abstract: In this paper J K s -band data from the VISTA Magellanic Cloud (VMC) survey are used to investigate the tip of the red giant branch (TRGB) as a distance indicator. A linear fit to recent theoretical models is used as the basis for the absolute calibration which reads M K s = −4.196 − 2.013 ( J − K s ), valid in the colour range 0.75 ( J − K s ) 1.3 mag and in the 2MASS system. The observed TRGB is found based on a classical first-order derivative filter and a second-order derivative filter applied to the binned luminosity function using the “sharpened” magnitude that takes the colour term into account. Extensive simulations are carried out to investigate any biases and errors in the derived distance modulus (DM). Based on these simulations criteria are established related to the number of stars per bin in the 0.5 mag range below the TRGB and related to the significance with which the peak in the filter response curve is determined such that the derived distances are unbiased. The DMs based on the second-order derivative filter are found to be more stable and are therefore adopted, although this requires twice as many stars per bin. Given the surface density of TRGB stars in the Magellanic Clouds (MCs), areas of ∼0.5 deg 2 in the densest parts to ∼10 deg 2 in the outskirts of the MCs need to be considered to obtain accurate and reliable values for the DMs. The TRGB method is applied to specific lines-of-sight where independent distance estimates exist, based on detached eclipsing binaries in the Large and Small Magellanic Clouds (LMC, SMC), classical Cepheids in the LMC, RR Lyrae stars in the SMC, and fields in the SMC where the star formation history (together with reddening and distance) has been derived from deep VMC data. The analysis shows that the theoretical calibration is consistent with the data, that the systematic error on the DM is approximately 0.045 mag (about evenly split between the theoretical calibration and the method), and that random errors of 0.015 mag are achievable. Reddening is an important element in deriving the distance: we derive mean DMs ranging from 18.92 mag (for a typical E ( B − V ) of 0.15 mag) to 19.07 mag ( E ( B − V )∼0.04 mag) for the SMC, and ranging from 18.48 mag ( E ( B − V )∼0.12 mag) to 18.57 mag ( E ( B − V )∼0.05 mag) for the LMC.
Publisher: Oxford University Press (OUP)
Date: 07-2009
Publisher: American Astronomical Society
Date: 07-2020
Abstract: The number of known periodic variables has grown rapidly in recent years. Thanks to its large field of view and faint limiting magnitude, the Zwicky Transient Facility (ZTF) offers a unique opportunity to detect variable stars in the northern sky. Here, we exploit ZTF Data Release 2 (DR2) to search for and classify variables down to r ∼ 20.6 mag. We classify 781,602 periodic variables into 11 main types using an improved classification method. Comparison with previously published catalogs shows that 621,702 objects (79.5%) are newly discovered or newly classified, including ∼700 Cepheids, ∼5000 RR Lyrae stars, ∼15,000 δ Scuti variables, ∼350,000 eclipsing binaries, ∼100,000 long-period variables, and about 150,000 rotational variables. The typical misclassification rate and period accuracy are on the order of 2% and 99%, respectively. 74% of our variables are located at Galactic latitudes, . This large s le of Cepheids, RR Lyrae, δ Scuti stars, and contact (EW-type) eclipsing binaries is helpful to investigate the Galaxy’s disk structure and evolution with an improved completeness, areal coverage, and age resolution. Specifically, the northern warp and the disk’s edge at distances of 15–20 kpc are significantly better covered than previously. Among rotational variables, RS Canum Venaticorum and BY Draconis-type variables can be separated easily. Our knowledge of stellar chromospheric activity would benefit greatly from a statistical analysis of these types of variables.
Publisher: Oxford University Press (OUP)
Date: 14-10-2019
Abstract: We present the results of the light curve model fitting technique applied to optical and near-infrared photometric data for a s le of 18 Classical Cepheids (11 fundamentals and 7 first overtones) in the Large Magellanic Cloud (LMC). We use optical photometry from the OGLE III data base and near-infrared photometry obtained by the European Southern Observatory public survey ‘VISTA near-infrared survey of the Magellanic Clouds system’. Iso-periodic non-linear convective model sequences have been computed for each selected Cepheid in order to reproduce the multifilter light-curve litudes and shape details. The inferred in idual distances provide an intrinsic weighted mean value for the LMC distance modulus of μ0 = 18.56 mag with a standard deviation of 0.13 mag. We derive also the Period–Radius, the Period–Luminosity, and the Period–Wesenheit relations that are consistent with similar relations in the literature. The intrinsic masses and luminosities of the best-fitting models show that all the investigated pulsators are brighter than the predictions of the canonical evolutionary mass–luminosity relation, suggesting a significant efficiency of non-canonical phenomena, such as overshooting, mass-loss, and/or rotation.
Publisher: American Astronomical Society
Date: 10-06-2014
Publisher: Oxford University Press (OUP)
Date: 06-02-2021
Abstract: The impact of stellar rotation on the morphology of star cluster colour–magnitude diagrams is widely acknowledged. However, the physics driving the distribution of the equatorial rotation velocities of main-sequence turn-off stars is as yet poorly understood. Using Gaia Data Release 2 photometry and new Southern African Large Telescope medium-resolution spectroscopy, we analyse the intermediate-age ($\\sim 1\\text{-}{\\rm Gyr}$-old) Galactic open clusters NGC 3960, NGC 6134, and IC 4756 and develop a novel method to derive their stellar rotation distributions based on SYCLIST stellar rotation models. Combined with literature data for the open clusters NGC 5822 and NGC 2818, we find a tight correlation between the number ratio of slow rotators and the clusters’ binary fractions. The blue-main-sequence stars in at least two of our clusters are more centrally concentrated than their red-main-sequence counterparts. The origin of the equatorial stellar rotation distribution and its evolution remains as yet unidentified. However, the observed correlation in our open cluster s le suggests a binary-driven formation mechanism.
Publisher: Oxford University Press (OUP)
Date: 05-2005
Publisher: Oxford University Press (OUP)
Date: 12-2004
Publisher: Springer Netherlands
Date: 2001
Publisher: Oxford University Press (OUP)
Date: 31-03-2021
Abstract: We present results from an analysis of ∼29 000 RR Lyrae stars located in the Large Magellanic Cloud (LMC). For these objects, near-infrared time-series photometry from the VISTA survey of the Magellanic Clouds system (VMC) and optical data from the Optical Gravitational Lensing Experiment (OGLE) IV survey and the Gaia Data Release 2 catalogue of confirmed RR Lyrae stars were exploited. Using VMC and OGLE IV magnitudes we derived period–luminosity (PL), period–luminosity–metallicity (PLZ), period–Wesenheit (PW), and period–Wesenheit–metallicity (PWZ) relations in all available bands. More that 7000 RR Lyrae were discarded from the analysis because they appear to be overluminous with respect to the PL relations. The $PL_{K_{\\mathrm{s}}}$ relation was used to derive in idual distance to ${\\sim}22\\, 000$ RR Lyrae stars, and study the three-dimensional structure of the LMC. The distribution of the LMC RR Lyrae stars is ellipsoidal with the three axis S1 = 6.5 kpc, S2 = 4.6 kpc, and S3 = 3.7 kpc, inclination i = 22 ± 4° relative to the plane of the sky and position angle of the line of nodes θ = 167 ± 7° (measured from north to east). The north-eastern part of the ellipsoid is closer to us and no particular associated substructures are detected and neither any metallicity gradient.
Publisher: Springer Netherlands
Date: 2001
Publisher: American Astronomical Society
Date: 10-07-2009
Publisher: EDP Sciences
Date: 23-10-2007
Publisher: American Astronomical Society
Date: 10-11-2016
Publisher: American Astronomical Society
Date: 17-11-2010
Publisher: American Astronomical Society
Date: 13-05-2015
Publisher: Oxford University Press (OUP)
Date: 10-2003
Publisher: Cambridge University Press (CUP)
Date: 08-2006
DOI: 10.1017/S1743921307001962
Abstract: Young, massive star clusters (YMCs) are the most notable and significant end products of violent star-forming episodes triggered by galaxy collisions and close encounters. The question remains, however, whether or not at least a fraction of the compact YMCs seen in abundance in extragalactic starbursts, are potentially the progenitors of (≳10 Gyr) old globular cluster (GC)-type objects. If we could settle this issue convincingly, one way or the other, the implications of such a result would have far-reaching implications for a wide range of astrophysical questions, including our understanding of the process of galaxy formation and assembly, and the process and conditions required for star (cluster) formation. Because of the lack of a statistically significant s le of YMCs in the Local Group, however, we need to resort to either statistical arguments or to the painstaking approach of case-by-case studies of in idual objects in more distant galaxies.
Publisher: Oxford University Press (OUP)
Date: 10-2006
Publisher: Springer Science and Business Media LLC
Date: 22-08-2017
Publisher: Cambridge University Press (CUP)
Date: 12-03-2015
Publisher: Cambridge University Press (CUP)
Date: 08-2009
DOI: 10.1017/S1743921309992079
Abstract: The presence of blue straggler stars (BSs) as secure members of star clusters poses a major challenge to the conventional picture of simple stellar population (SSP) models. The models are based on the stellar evolution theory of single stars, while the major formation mechanisms of BSs are all correlated with stellar interactions. Based on a sufficient working s le including 100 Galactic open clusters, one Galactic globular cluster, and seven Magellanic Cloud star clusters, we discuss the modifications of the properties of broad-band colors and Lick indices of the standard SSP models due to BS populations.
Publisher: Oxford University Press (OUP)
Date: 29-07-2017
Publisher: Springer Netherlands
Date: 1995
Publisher: Oxford University Press (OUP)
Date: 11-08-2002
Publisher: American Astronomical Society
Date: 03-2021
Abstract: We present new near-infrared, JHK s , period–luminosity relations (PLRs) for RR Lyrae variables in the Messier 53 (M53 or NGC 5024) globular cluster. Multi-epoch JHK s observations, obtained with the WIRCam instrument on the 3.6 m Canada–France–Hawaii Telescope, are used for the first time to estimate precise mean magnitudes for 63 RR Lyrae stars in M53 including 29 fundamental-mode (RRab) and 34 first-overtone mode (RRc) variables. The JHK s -band PLRs for RR Lyrae stars are best constrained for RRab types with a minimal scatter of 22, 23, and 19 mmag, respectively. The combined s le of RR Lyrae is used to derive the K s -band PLR, K s = − 2.303 ( 0.063 ) log P + 15.212 ( 0.016 ) , exhibiting a 1 σ dispersion of only 0.027 mag. Theoretical period–luminosity–metallicity (PLZ) relations are used to predict parallaxes for 400 Galactic RR Lyrae, resulting in a median parallax zero-point offset of −7 ± 3 μ as in Gaia Early Data Release 3 (EDR3), which increases to 22 ± 2 μ as if the parallax corrections are applied. We also estimate a robust distance modulus, μ M53 = 16.403 ± 0.024 (statistical) ± 0.033 (systematic) mag, to M53 based on theoretical calibrations. Homogeneous and precise mean magnitudes for RR Lyrae in M53 together with similar literature data for M3, M4, M5, and ω Cen are used to empirically calibrate a new RR Lyrae PLZ K s relation, K s = − 0.848 ( 0.007 ) − 2.320 ( 0.006 ) log P + 0.166 ( 0.011 ) [ Fe / H ] , anchored with Gaia EDR3 distances and theoretically predicted relations, and to simultaneously estimate precise RR Lyrae-based distances to these globular clusters.
Publisher: Wiley
Date: 28-01-2016
DOI: 10.1111/CEA.12645
Abstract: Exposure to low levels of vitamin D in fetal life might be a risk factor for childhood asthma. We examined whether 25-hydroxyvitamin D levels in mid-gestation and at birth were associated with higher airway resistance and inflammation, and increased risks of wheezing and asthma in school-age children. We performed a population-based prospective cohort study among 3130 mothers and their children. Maternal blood s les in mid-gestation and umbilical cord blood s les at birth were used to determine 25-hydroxyvitamin D levels. At age of 6, airway resistance (Rint) was measured by interrupter technique and airway inflammation by fractional exhaled nitric oxide (FENO) using NIOX chemiluminescence analyser. Wheezing and asthma were prospectively assessed by annual questionnaires until age 6. Maternal levels of 25-hydroxyvitamin D in mid-gestation were not associated with Rint, FeNO, wheezing patterns, or asthma. Children in the lowest tertile of 25-hydroxyvitamin D levels at birth had a higher Rint (Z-score (95% confidence interval [95% CI]): -0.42 (-0.84, -0.01), P-value for trend< 0.05), compared to those in the highest tertile group. The effect estimate attenuated when child's current 25-hydroxyvitamin D level was taken into account [Z-score (95% CI): -0.55 (-1.08, 0.01)]. Low levels of 25-hydroxyvitamin D at birth were associated with a higher airway resistance in childhood. Additional adjustment for child's current 25-hydroxyvitamin D level reduced the effect size of the association. Further studies are needed to replicate these findings and to examine mechanisms underlying the observed association and the long-term consequences.
Publisher: Oxford University Press (OUP)
Date: 07-2001
Publisher: Oxford University Press (OUP)
Date: 30-08-2021
Abstract: We have derived high-spatial-resolution metallicity maps covering ∼105 deg2 across the Large Magellanic Cloud (LMC) using near-infrared passbands from the VISTA Survey of the Magellanic Clouds. We attempt to understand the metallicity distribution and gradients of the LMC up to a radius of ∼6 kpc. We identify red giant branch (RGB) stars in spatially distinct Y, (Y − Ks) colour–magnitude diagrams. In any of our selected subregions, the RGB slope is used as an indicator of the average metallicity, based on calibration to metallicity using spectroscopic data. The mean LMC metallicity is [Fe/H] = −0.42 dex (σ[Fe/H] = 0.04 dex). We find the bar to be mildly metal-rich compared with the outer disc, showing evidence of a shallow gradient in metallicity (−0.008 ± 0.001 dex kpc−1) from the galaxy’s centre to a radius of 6 kpc. Our results suggest that the LMC’s stellar bar is chemically similar to the bars found in large spiral galaxies. The LMC’s radial metallicity gradient is asymmetric. It is metal-poor and flatter towards the southwest, in the direction of the Bridge. This hints at mixing and/or distortion of the spatial metallicity distribution, presumably caused by tidal interactions between the Magellanic Clouds.
Publisher: American Astronomical Society
Date: 30-01-2019
Publisher: American Astronomical Society
Date: 10-01-2017
Publisher: American Astronomical Society
Date: 21-03-2018
Publisher: Cambridge University Press (CUP)
Date: 08-2021
DOI: 10.1017/S1743921322005038
Abstract: The VISTA Magellanic Clouds Survey (VMC) is a near-infrared survey of the Magellanic system. The VMC data has been exploited to detect and study statistically correlated young groups of stars — also known as “young stellar structures” — in the Large and Small Magellanic Clouds (LMC and SMC). We showcase the ∼ 3000 recently detected young stellar structures in the LMC and their similarity to the fractal interstellar medium. We discuss how their properties indicate their formation mechanisms and that there are no preferred scales of star formation in the LMC.
Publisher: Cambridge University Press (CUP)
Date: 2008
DOI: 10.1071/AS07046
Abstract: The Magellanic System represents one of the best places to study the formation and evolution of galaxies. Photometric surveys of various depths, areas and wavelengths have had a significant impact on our understanding of the system however, a complete picture is still lacking. VMC (the VISTA near-infrared YJK s survey of the Magellanic System) will provide new data to derive the spatially resolved star formation history and to construct a three-dimensional map of the system. These data combined with those from other ongoing and planned surveys will give us an absolutely unique view of the system opening up the doors to truly new science!
Publisher: American Astronomical Society
Date: 04-06-2014
Publisher: American Astronomical Society
Date: 09-11-2017
Publisher: EDP Sciences
Date: 09-2012
Publisher: Oxford University Press (OUP)
Date: 26-10-2010
Publisher: Oxford University Press (OUP)
Date: 19-03-2015
DOI: 10.1093/MNRAS/STV141
Publisher: Springer Netherlands
Date: 19-12-2009
Publisher: American Astronomical Society
Date: 23-11-2016
Publisher: American Astronomical Society
Date: 04-2021
Abstract: We independently determine the zero-point offset of the Gaia early Data Release-3 (EDR3) parallaxes based on ∼110,000 W Ursae Majoris (EW)-type eclipsing binary systems. EWs cover almost the entire sky and are characterized by a relatively complete coverage in magnitude and color. They are an excellent proxy for Galactic main-sequence stars. We derive a W1-band period–luminosity relation with a distance accuracy of 7.4%, which we use to anchor the Gaia parallax zero-point. The final, global parallax offsets are −28.6 ± 0.6 μ as and −25.4 ± 4.0 μ as (before correction) and 4.2 ± 0.5 μ as and 4.6 ± 3.7 μ as (after correction) for the five- and six-parameter solutions, respectively. The total systematic uncertainty is 1.8 μ as. The spatial distribution of the parallax offsets shows that the bias in the corrected Gaia EDR3 parallaxes is less than 10 μ as across 40% of the sky. Only 15% of the sky is characterized by a parallax offset greater than 30 μ as. Thus, we have provided independent evidence that the parallax zero-point correction provided by the Gaia team significantly reduces the prevailing bias. Combined with literature data, we find that the overall Gaia EDR3 parallax offsets for Galactic stars are [−20, −30] μ as and 4–10 μ as, respectively, before and after correction. For specific regions, an additional deviation of about 10 μ as is found.
Publisher: Oxford University Press (OUP)
Date: 30-09-2015
Publisher: Oxford University Press (OUP)
Date: 10-2002
Publisher: Public Library of Science (PLoS)
Date: 08-10-2015
Publisher: Springer Berlin Heidelberg
Date: 2009
Publisher: American Astronomical Society
Date: 02-2001
DOI: 10.1086/318771
Publisher: Oxford University Press (OUP)
Date: 24-07-2020
Abstract: We have derived high-spatial-resolution metallicity maps covering ∼42 deg2 across the Small Magellanic Cloud (SMC) in an attempt to understand its metallicity distribution and gradients up to a radius of ∼4○. Using the near-infrared VISTA Survey of the Magellanic Clouds, our data cover a thrice larger area compared with previous studies. We identify red giant branch (RGB) stars in spatially distinct Y, (Y − Ks) colour–magnitude diagrams. In any of our selected subregions, the RGB slope is used as an indicator of the average metallicity, based on calibration to metallicity using spectroscopic data. The metallicity distribution across the SMC is unimodal and can be fitted by a Gaussian distribution with a peak at [Fe/H] = −0.97 dex (σ[Fe/H] = 0.05 dex). We find evidence of a shallow gradient in metallicity (−0.031 ± 0.005 dex deg−1) from the Galactic Centre to radii of 2○–2${_{.}^{\\circ}}$5, followed by a flat metallicity trend from ∼3${_{.}^{\\circ}}$5 to 4○. We find that the SMC’s metallicity gradient is radially asymmetric. It is flatter towards the east than to the west, hinting at mixing and/or distortion of the spatial metallicity distribution (within the inner 3○), presumably caused by tidal interactions between the Magellanic Clouds.
Publisher: Springer Science and Business Media LLC
Date: 29-09-2009
Publisher: Oxford University Press (OUP)
Date: 24-01-2017
DOI: 10.1093/MNRAS/STX205
Publisher: Frontiers Media SA
Date: 21-11-2022
Publisher: American Astronomical Society
Date: 18-01-2021
Publisher: Oxford University Press (OUP)
Date: 07-2004
Publisher: Oxford University Press (OUP)
Date: 12-2006
Publisher: Springer Netherlands
Date: 2002
Publisher: Springer-Verlag
Date: 2003
DOI: 10.1007/10857603_6
Publisher: Oxford University Press (OUP)
Date: 06-2007
Publisher: EDP Sciences
Date: 04-2020
DOI: 10.1051/0004-6361/201937271
Abstract: Context. Variability is a key property of stars on the asymptotic giant branch (AGB). Their pulsation period is related to the luminosity and mass-loss rate of the star. Long-period variables (LPVs) and Mira variables are the most prominent of all types of variability of evolved stars. The reddest, most obscured AGB stars are too faint in the optical and have eluded large variability surveys. Aims. We obtained a s le of LPVs by analysing K -band light curves (LCs) of a large number of sources in the direction of the Magellanic Clouds with the colours expected for red AGB stars (( J − K ) 3 mag or equivalent in other colour combinations). Methods. Selection criteria were derived based on colour-colour and colour-magnitude diagrams from the combination of the VISTA Magellanic Cloud (VMC) survey, Spitzer IRAC and AllWISE data. After eliminating LPVs with known periods shorter than 450 days, a s le of 1299 candidate obscured AGB stars was selected. K -band LCs were constructed by combining the epoch photometry available in the VMC survey with literature data, were analysed for variability, and fitted with a single period sine curve to derive mean magnitudes, litudes, and periods. A subset of 254 stars are either new variables, known variables where the period we find is better determined than the literature value, or variables with periods longer than 1000 days. The spectral energy distributions (SEDs) of these stars were fitted to a large number of templates. For this purpose the SEDs and Spitzer IRS spectra of some non-AGB stars (Be stars, H II regions and young stellar objects – YSOs) were also fitted to have templates of the most likely contaminants in the s le. Results. A s le of 217 likely LPVs is found. Thirty-four stars have periods longer than 1000 days, although some of them have alternative shorter periods. The longest period of a known Mira in the Magellanic Clouds from Optical Gravitational Lensing Experiment data (with P = 1810 d) is derived to have a period of 2075 d based on its infrared LC. Two stars are found to have longer periods, but both have lower luminosities and smaller pulsation litudes than expected for Miras. Mass-loss rates and luminosities are estimated from the template fitting. Period-luminosity relations are presented for carbon (C-) and oxygen (O-) rich Miras that appear to be extensions of relations derived in the literature for shorter periods. The fit for the C stars is particularly well defined (with 182 objects) and reads M bol = (−2.27 ± 0.20) ⋅ log P + (1.45 ± 0.54) mag with an rms of 0.41 mag. Thirty-four stars show pulsation properties typical of Miras while the SEDs indicate that they are not. Overall, the results of the LC fitting are presented for over 200 stars that are associated with YSOs.
Publisher: China Science Publishing & Media Ltd.
Date: 03-2022
Publisher: American Astronomical Society
Date: 05-03-2010
Publisher: Cambridge University Press (CUP)
Date: 06-2019
DOI: 10.1017/S174392131900869X
Abstract: We have collected 2330 Cepheids to establish an intuitive 3D map of the Milky Way’s disk. As regards the warp litude, the Cepheid disk agrees well with the gas disk for radii up to 15 kpc. However, the mean line of nodes (LON) of the Cepheid disk deviates from the Galactic Center–Sun direction by 17.5±1.0°. This is a new and different result compared with previous results. The LON is not stable at any given radius, but it twists. The twisted pattern suggests that the formation of the Milky Way’s warp is dominated by the massive inner disk. The kinematic warp defined by the Cepheids is also in concordance with the spatial warp. In the 2020 era, the anticipated increasing number of new Cepheids will provide a key opportunity to view our Milky Way’s disk as a whole, and we expect that our knowledge of the disk’s main structural features will be much improved.
Publisher: MDPI AG
Date: 15-11-2021
Abstract: Cool stars with convective envelopes of spectral types F and later tend to exhibit magnetic activity throughout their atmospheres. The presence of strong and variable magnetic fields is evidenced by photospheric starspots, chromospheric plages and coronal flares, as well as by strong Ca ii H+K and Hα emission, combined with the presence of ultraviolet resonance lines. We review the drivers of stellar chromospheric activity and the resulting physical parameters implied by the observational diagnostics. At a basic level, we explore the importance of stellar dynamos and their activity cycles for a range of stellar types across the Hertzsprung–Russell diagram. We focus, in particular, on recent developments pertaining to stellar rotation properties, including the putative Vaughan–Preston gap. We also pay specific attention to magnetic variability associated with close binary systems, including RS Canum Venaticorum, BY Draconis, W Ursae Majoris and Algol binaries. At the present time, large-scale photometric and spectroscopic surveys are becoming generally available, thus leading to a resurgence of research into chromospheric activity. This opens up promising prospects to gain a much improved understanding of chromospheric physics and its wide-ranging impact.
Publisher: IOP Publishing
Date: 2011
DOI: 10.1086/658162
Publisher: Springer Science and Business Media LLC
Date: 03-11-2009
Publisher: IOP Publishing
Date: 11-2017
Publisher: Springer Berlin Heidelberg
Date: 2009
Publisher: American Astronomical Society
Date: 04-2003
DOI: 10.1086/367820
Publisher: American Astronomical Society
Date: 11-03-2021
Abstract: We present a catalog of eclipsing binaries in the northern Galactic plane from the Kiso Wide-Field Camera Intensive Survey of the Galactic Plane (KISOGP). We visually identified 7055 eclipsing binaries spread across ∼330 deg 2 , including 4197 W Ursa Majoris/EW-type, 1458 β Lyrae/EB-type, and 1400 Algol/EA-type eclipsing binaries. For all systems, I -band light curves were used to obtain accurate system parameters. We derived the distances and extinction values for the EW-type objects from their period–luminosity relation. We also obtained the structure of the thin disk from the distribution of our s le of eclipsing binary systems, combined with those of high-mass star-forming regions and Cepheid tracers. We found that the thin disk is inhomogeneous in number density as a function of Galactic longitude. Using this new set of distance tracers, we constrain the detailed structure of the thin disk. Finally, we report a global parallax zero-point offset of Δ π = −42.1 ± 1.9 (stat.) ± 12.9 (syst.) μ as between our carefully calibrated EW-type eclipsing binary positions and those provided by Gaia Early Data Release 3. Implementation of the officially recommended parallax zero-point correction results in a significantly reduced offset. Additionally, we provide a photometric characterization of our EW-type eclipsing binaries that can be applied to further analyses.
Publisher: American Astronomical Society
Date: 23-04-2018
Publisher: Springer Berlin Heidelberg
Date: 1996
Publisher: Springer Science and Business Media LLC
Date: 27-01-2016
DOI: 10.1038/NATURE16493
Abstract: Stars in clusters are thought to form in a single burst from a common progenitor cloud of molecular gas. However, massive, old 'globular' clusters--those with ages greater than ten billion years and masses several hundred thousand times that of the Sun--often harbour multiple stellar populations, indicating that more than one star-forming event occurred during their lifetimes. Colliding stellar winds from late-stage, asymptotic-giant-branch stars are often suggested to be triggers of second-generation star formation. For this to occur, the initial cluster masses need to be greater than a few million solar masses. Here we report observations of three massive relatively young star clusters (1-2 billion years old) in the Magellanic Clouds that show clear evidence of burst-like star formation that occurred a few hundred million years after their initial formation era. We show that such clusters could have accreted sufficient gas to form new stars if they had orbited in their host galaxies' gaseous disks throughout the period between their initial formation and the more recent bursts of star formation. This process may eventually give rise to the ubiquitous multiple stellar populations in globular clusters.
Publisher: Oxford University Press (OUP)
Date: 11-07-2014
Publisher: American Astronomical Society
Date: 16-04-2014
Publisher: Springer Science and Business Media LLC
Date: 04-01-2017
Publisher: Cambridge University Press (CUP)
Date: 2005
DOI: 10.1017/S1539299600015690
Abstract: Based on new spectra spanning wavelengths from 0.8 to 2.4 μm , we study the properties of bright near-IR clusters in M82. We focus on age and extinction, which are critical parameters when one uses dynamical masses to constrain the stellar IMF. The modelling of red supergiant evolution by various authors leads to very significant differences in synthetic cluster spectra. Near-IR fluxes alone therefore do not rule out a normal IMF for cluster F, previously found to be deficient in low mass stars. Combined optical and near-IR studies are being undertaken.
Publisher: Oxford University Press (OUP)
Date: 17-12-2016
Publisher: American Astronomical Society
Date: 09-01-2018
Publisher: Informa UK Limited
Date: 05-2012
Publisher: American Astronomical Society
Date: 11-2021
Abstract: Angular momentum is a key property regulating star formation and evolution. However, the physics driving the distribution of the stellar rotation rates of early-type main-sequence stars is as yet poorly understood. Using our catalog of 40,034 early-type stars with homogeneous v sin i parameters, we review the statistical properties of their stellar rotation rates. We discuss the importance of possible contaminants, including binaries and chemically peculiar stars. Upon correction for projection effects and rectification of the error distribution, we derive the distributions of our s le’s equatorial rotation velocities, which show a clear dependence on stellar mass. Stars with masses less than 2.5 M ⊙ exhibit a unimodal distribution, with the peak velocity ratio increasing as stellar mass increases. A bimodal rotation distribution, composed of two branches of slowly and rapidly rotating stars, emerges for more massive stars ( M 2.5 M ⊙ ). For stars more massive than 3.0 M ⊙ , the gap between the bifurcated branches becomes prominent. For the first time, we find that metal-poor ([M/H] −0.2 dex) stars only exhibit a single branch of slow rotators, while metal-rich ([M/H] 0.2 dex) stars clearly show two branches. The difference could be attributed to unexpectedly high spin-down rates and/or in part strong magnetic fields in the metal-poor subs le.
Publisher: American Astronomical Society
Date: 05-02-2018
Publisher: IOP Publishing
Date: 09-2018
Publisher: American Astronomical Society
Date: 18-03-2014
Publisher: Wiley
Date: 02-09-2011
Publisher: EDP Sciences
Date: 12-2018
DOI: 10.1051/0004-6361/201833951
Abstract: Context . Detailed studies of intermediate- and low-mass pre-main-sequence (PMS) stars outside the Galaxy have so far been conducted only for small targeted regions harbouring known star formation complexes. The VISTA Survey of the Magellanic Clouds (VMC) provides an opportunity to study PMS populations down to solar masses on a galaxy-wide scale. Aims . Our goal is to use near-infrared data from the VMC survey to identify and characterise PMS populations down to ∼1 M ⊙ across the Magellanic Clouds. We present our colour–magnitude diagram method, and apply it to a ∼1.5 deg 2 pilot field located in the Large Magellanic Cloud. Methods . The pilot field is ided into equal-size grid elements. We compare the stellar population in every element with the population in nearby control fields by creating K s /( Y − K s ) Hess diagrams the observed density excesses over the local field population are used to classify the stellar populations. Results . Our analysis recovers all known star formation complexes in this pilot field (N 44, N 51, N 148, and N 138) and for the first time reveals their true spatial extent. In total, around 2260 PMS candidates with ages ≲10 Myr are found in the pilot field. PMS structures, identified as areas with a significant density excess of PMS candidates, display a power-law distribution of the number of members with a slope of −0.86 ± 0.12. We find a clustering of the young stellar populations along ridges and filaments where dust emission in the far-infrared (FIR) (70 μ m–500 μ m) is bright. Regions with young populations lacking massive stars show a lower degree of clustering and are usually located in the outskirts of the star formation complexes. At short FIR wavelengths (70 μ m,100 μ m) we report a strong dust emission increase in regions hosting young massive stars, which is less pronounced in regions populated only by less massive (≲4 M ⊙ ) PMS stars.
Publisher: Wiley
Date: 02-09-2011
Publisher: Wiley
Date: 02-09-2011
Publisher: Wiley
Date: 02-09-2011
Publisher: American Astronomical Society
Date: 06-2018
Publisher: EDP Sciences
Date: 17-05-2006
Publisher: Wiley
Date: 02-09-2011
Publisher: Oxford University Press (OUP)
Date: 04-2008
Publisher: American Astronomical Society
Date: 27-01-2017
Publisher: Springer Science and Business Media LLC
Date: 02-09-2009
Publisher: American Astronomical Society
Date: 29-04-2009
Publisher: EDP Sciences
Date: 31-05-2013
Publisher: Cambridge University Press (CUP)
Date: 2005
DOI: 10.1017/S1539299600015562
Abstract: The currently available empirical evidence on the star formation processes in the extreme, high-pressure environments induced by galaxy encounters, mostly based on high-resolution Hubble Space Telescope imaging observations, strongly suggests that star cluster formation is an important and perhaps even the dominant mode of star formation in the starburst events associated with galaxy interactions.
Publisher: Oxford University Press (OUP)
Date: 11-06-2003
Publisher: Wiley
Date: 02-09-2011
Publisher: Springer Science and Business Media LLC
Date: 17-09-2009
Publisher: EDP Sciences
Date: 02-2004
Publisher: EDP Sciences
Date: 04-2018
DOI: 10.1051/0004-6361/201732144
Abstract: We use deep multi-epoch point-spread function (PSF) photometry taken with the Visible and Infrared Survey Telescope for Astronomy (VISTA) to measure and analyze the proper motions of stars within the Galactic globular cluster 47 Tucanae (47 Tuc, NGC 104). The observations are part of the ongoing near-infrared VISTA survey of the Magellanic Cloud system (VMC). The data analyzed in this study correspond to one VMC tile, which covers a total sky area of 1.77 deg 2 . Absolute proper motions with respect to ~9070 background galaxies are calculated from a linear regression model applied to the positions of stars in 11 epochs in the K s filter. The data extend over a total time baseline of about 17 months. We found an overall median proper motion of the stars within 47 Tuc of ( μ α cos( δ ), μ δ ) = (+5.89 ± 0.02 (statistical) ± 0.13 (systematic), −2.14 ± 0.02 (statistical) ± 0.08 (systematic)) mas yr −1 , based on the measurements of ~35 000 in idual sources between 5′ and 42′ from the cluster center. We compared our result to the proper motions from the newest US Naval Observatory CCD Astrograph Catalog (UCAC5), which includes data from the Gaia data release 1. Selecting cluster members ( ~2700 stars), we found a median proper motion of ( μ α cos( δ ), μ δ ) = (+5.30 ± 0.03 (statistical) ± 0.70 (systematic), −2.70 ± 0.03 (statistical) ± 0.70 (systematic)) mas yr −1 . Comparing the results with measurements in the literature, we found that the values derived from the VMC data are consistent with the UCAC5 result, and are close to measurements obtained using the Hubble Space Telescope. We combined our proper motion results with radial velocity measurements from the literature and reconstructed the orbit of 47 Tuc, finding that the cluster is on an orbit with a low ellipticity and is confined within the inner ~7.5 kpc of the Galaxy. We show that the use of an increased time baseline in combination with PSF-determined stellar centroids in crowded regions significantly improves the accuracy of the method. In future works, we will apply the methods described here to more VMC tiles to study in detail the kinematics of the Magellanic Clouds.
Publisher: Oxford University Press (OUP)
Date: 10-2003
Publisher: Cambridge University Press (CUP)
Date: 09-2007
DOI: 10.1017/S1743921308015755
Abstract: The total mass of a distant star cluster is often derived from the virial theorem, using line-of-sight velocity dispersion measurements and half-light radii, under the implicit assumption that all stars are single (although it is known that most stars form part of binary systems). The components of binary stars exhibit orbital motion, which increases the measured velocity dispersion, resulting in a dynamical mass overestimation. In these proceedings we quantify the effect of neglecting the binary population on the derivation of the dynamical mass of a star cluster. We find that the presence of binaries plays an important role for clusters with total mass M cl ≤ 10 5 M ⊙ the dynamical mass can be significantly overestimated (by a factor of two or more). For the more massive clusters, with M cl ≥ 10 5 M ⊙ , binaries do not affect the dynamical mass estimation significantly, provided that the cluster is significantly compact (half-mass radius ≤qslant 5 pc).
Publisher: Oxford University Press (OUP)
Date: 28-06-2018
Publisher: IOP Publishing
Date: 02-2018
Publisher: Cambridge University Press (CUP)
Date: 2005
DOI: 10.1017/S1539299600015574
Abstract: Evolutionary synthesis models for star clusters of various metallicities, including gaseous emission during the lifetime of the ionizing stars, are used to model star cluster systems comprising two populations: an old metal-poor globular cluster (GC) population similar to that of the Milky Way halo, and a second GC population of arbitrary metallicity. We investigate the time evolution of color distributions and luminosity functions for the two GC populations and compare with observations of E/SO galaxies. We show that multi-passband data for GC populations give clues to the relative ages and metallicities of the two subpopulations, and help constrain formation scenarios for their parent galaxies.
Publisher: Elsevier BV
Date: 2017
Publisher: American Astronomical Society
Date: 11-2002
DOI: 10.1086/341556
Publisher: Oxford University Press (OUP)
Date: 21-11-1999
Publisher: American Astronomical Society
Date: 20-01-2003
DOI: 10.1086/367928
Publisher: American Astronomical Society
Date: 10-2022
Abstract: In addition to the extended main-sequence turnoffs widely found in young and intermediate-age (∼600 Myr to 2 Gyr old) star clusters, some younger clusters even exhibit split main sequences (MSs). Different stellar rotation rates are proposed to account for the bifurcated MS pattern, with red and blue MSs (rMS and bMS) populated by fast and slowly rotating stars, respectively. Using photometry from Gaia Early Data Release 3, we report a Galactic open cluster with a bifurcated MS, NGC 2422 (∼90 Myr). We exclude the possibilities that the bifurcated MS pattern is caused by photometric noise or differential reddening. We aim to examine if stellar rotation can account for the split MS. We use spectra observed with the Canada–France–Hawaii Telescope and the Southern African Large Telescope and directly measured v sin i , the projected rotational velocities, for stars populating the bMS and rMS. We find that their v sin i values are weakly correlated with their loci in the color–magnitude diagram because of contamination caused by a large fraction of rMS stars with low projected rotational velocities. Based on the spectral energy distribution fitting method, we suggest that these slowly rotating stars at the rMS may hide a binary companion, which breaks the expected v sin i –color correlation. Future time-domain studies focusing on whether these slowly rotating stars are radial velocity variables are crucial to test the roles of stellar rotation and binarity in generating the split MSs.
Publisher: Springer Science and Business Media LLC
Date: 11-02-2015
DOI: 10.1038/NATURE14177
Publisher: EDP Sciences
Date: 2014
DOI: 10.1051/EAS/1567068
Publisher: Oxford University Press (OUP)
Date: 02-12-2014
Publisher: Oxford University Press (OUP)
Date: 16-06-2022
Abstract: We present an extensive catalogue of BY Draconis (BY Dra)-type variables and their stellar parameters. BY Dra are main-sequence FGKM-type stars. They exhibit inhomogeneous starspots and bright faculae in their photospheres. These features are caused by stellar magnetic fields, which are carried along with the stellar disc through rotation and which produce gradual modulations in their light curves (LCs). Our main objective is to characterize the properties of BY Dra variables over a wide range of stellar masses, temperatures, and rotation periods. A recent study categorized 84 697 BY Dra variables from Data Release 2 of the Zwicky Transient Facility based on their LCs. We have collected additional photometric data from multiple surveys and performed broad-band spectral energy distribution fits to estimate stellar parameters. We found that more than half of our s le objects are of K spectral type, covering an extensive range of stellar parameters in the low-mass regime (0.1–1.3 M⊙). Compared with previous studies, most of the sources in our catalogue are rapid rotators, and so most of them must be young stars for which a spin-down has not yet occurred. We sub ided our catalogue based on convection zone depth and found that the photospheric activity index, Sph, is lower for higher effective temperatures, i.e. for thinner convective envelopes. We observe a broad range of photospheric magnetic activity for different spectral classes owing to the presence of stellar populations of different ages. We found a higher magnetically active fraction for K- than M-type stars.
Publisher: No publisher found
Date: 2017
Publisher: Oxford University Press (OUP)
Date: 11-2013
Publisher: Oxford University Press (OUP)
Date: 28-06-2022
Abstract: The distribution of young stars into OB associations has long been in need of updating. High-precision Gaia Early Data Release 3 astrometry, coupled with modern machine-learning methods, allows this to be done. We have compiled a well-defined s le which includes OB stars and young open clusters (OCs), in total comprising about 47 700 objects. To break the s le down into groupings resembling associations, we applied the HDBSCAN* clustering algorithm. We used a Monte Carlo method to estimate the kinematic ages of the resulting clusters and the Student’s t-test to assess the significance of the linear correlations between proper motions and coordinates, indicating the presence of possible cluster expansion signatures. The ages of the majority of clusters demonstrating a general expansion at a 1σ confidence level are several tens of Myr, which is in agreement with the expected ages of OB associations. We found 32 OCs which turned out to be members of the resulting groupings their ages are consistent with one another within the uncertainties. Comparison of the clusters thus obtained with the historical composition of OB associations in the literature shows a correspondence between their positions in the Galaxy but an apparent absence of good one-to-one stellar matches. Therefore, we suggest that the historical composition of OB associations needs to be revised.
Publisher: Oxford University Press (OUP)
Date: 21-03-2003
Publisher: EDP Sciences
Date: 08-2011
Publisher: Oxford University Press (OUP)
Date: 09-1998
Publisher: Springer Science and Business Media LLC
Date: 2002
Publisher: Cambridge University Press (CUP)
Date: 05-2019
DOI: 10.1017/S1743921319006628
Abstract: We present a detailed analysis of the projected stellar rotational velocities of the well-separated double main sequence (MS) in the young, ∼200 Myr-old Milky Way open cluster NGC 2287 and suggest that stellar rotation may drive the split MSs in NGC 2287. We find that the observed distribution of projected stellar rotation velocities could result from a dichotomous distribution of stellar rotation rates. We discuss whether our observations may reflect the effects of tidal locking affecting a fraction of the cluster’s member stars in stellar binary systems. The slow rotators are likely stars that initially rotated rapidly but subsequently slowed down through tidal locking induced by low-mass-ratio binary systems. However, the cluster may have a much larger population of short-period binaries than is usually seen in the literature, with relatively low secondary masses.
Publisher: Springer Science and Business Media LLC
Date: 28-10-2014
DOI: 10.1038/NCOMMS6068
Abstract: Statins effectively lower LDL cholesterol levels in large studies and the observed interin idual response variability may be partially explained by genetic variation. Here we perform a pharmacogenetic meta-analysis of genome-wide association studies (GWAS) in studies addressing the LDL cholesterol response to statins, including up to 18,596 statin-treated subjects. We validate the most promising signals in a further 22,318 statin recipients and identify two loci, SORT1/CELSR2/PSRC1 and SLCO1B1 , not previously identified in GWAS. Moreover, we confirm the previously described associations with APOE and LPA. Our findings advance the understanding of the pharmacogenetic architecture of statin response.
Publisher: American Astronomical Society
Date: 22-09-2017
Publisher: Oxford University Press (OUP)
Date: 10-06-2022
Abstract: We present a map of the total intrinsic reddening across ≃ 90 deg2 of the Large Magellanic Cloud (LMC) derived using optical (ugriz) and near-infrared (IR YJKs) spectral energy distributions (SEDs) of background galaxies. The reddening map is created from a s le of 222 752 early-type galaxies based on the lephareχ2 minimization SED-fitting routine. We find excellent agreement between the regions of enhanced intrinsic reddening across the central (4 × 4 deg2) region of the LMC and the morphology of the low-level pervasive dust emission as traced by far-IR emission. In addition, we are able to distinguish smaller, isolated enhancements that are coincident with known star-forming regions and the clustering of young stars observed in morphology maps. The level of reddening associated with the molecular ridge south of 30 Doradus is, however, smaller than in the literature reddening maps. The reduced number of galaxies detected in this region, due to high extinction and crowding, may bias our results towards lower reddening values. Our map is consistent with maps derived from red clump stars and from the analysis of the star formation history across the LMC. This study represents one of the first large-scale categorizations of extragalactic sources behind the LMC and as such we provide the lephare outputs for our full s le of ∼ 2.5 million sources.
Publisher: Oxford University Press (OUP)
Date: 05-2007
Publisher: American Astronomical Society
Date: 02-08-2018
Publisher: Cambridge University Press (CUP)
Date: 10-2013
DOI: 10.1017/S1743921314000477
Abstract: We present the dependence of the amount of nuclear star formation on the non-axisymmetry of a bulge of disk galaxies. For this, we use a volume-limited s le of spiral galaxies at 0.02 = z 0.055 from the SDSS DR7. Among 3173 final s le galaxies with an axis ratio b/a 0.6 and a bulge fraction ranged in B/T = 0.41, nuclear starburst galaxies are 10%. We find that a fraction of the nuclear starburst galaxies become higher when ellipticity of a bulge increases in early type galaxies. Also, the fraction increases clearly when early type galaxies are isolated and in low density region. Our results indicate that the non-axisymmetry of bulges assists gas to fall inside and affects the nuclear starburst process in disk galaxies.
Publisher: Oxford University Press (OUP)
Date: 09-2013
Publisher: Oxford University Press (OUP)
Date: 25-09-2013
Publisher: Springer Science and Business Media LLC
Date: 21-11-2016
Publisher: American Astronomical Society
Date: 10-12-2007
DOI: 10.1086/522693
Publisher: EDP Sciences
Date: 16-02-2005
Publisher: Cambridge University Press (CUP)
Date: 2004
DOI: 10.1017/S0074180900197529
Abstract: Young clusters are observed to form in a variety of interacting galaxies and violent starbursts, a substantial number resembling the progenitors of the well-studied globular clusters in mass and size. By studying young clusters in merger remnants and peculiar galaxies, we can therefore learn about the violent star formation history of these galaxies. We present a new set of evolutionary synthesis models of our GALEV code specifically developed to include the gaseous emission of presently forming star clusters, and a new tool that allows to determine in idual cluster metallicities, ages, extinction values and masses from a comparison of a large grid of model S pectral E nergy D istributions (SEDs) with multi-color observations. First results for the newly-born clusters in NGC 1569 are presented.
Publisher: Oxford University Press (OUP)
Date: 09-2002
Publisher: American Astronomical Society
Date: 20-02-2009
Publisher: EDP Sciences
Date: 11-2018
DOI: 10.1051/0004-6361/201833538
Abstract: Context. Type II Cepheids (T2Cs) are radially pulsating variables that trace old stellar populations and provide distance estimates through their period-luminosity (PL) relation. Aims. We trace the structure of old stellar population in the Galactic bulge using new distance estimates and kinematic properties of T2Cs. Methods. We present new near-infrared photometry of T2Cs in the bulge from the VISTA Variables in the Vía Láctea survey (VVV). We provide the largest s le (894 stars) of T2Cs with JHK s observations that have accurate periods from the Optical Gravitational Lensing Experiment (OGLE) catalog. Our analysis makes use of the K s -band time-series observations to estimate mean magnitudes and in idual distances by means of the PL relation. To constrain the kinematic properties of our targets, we complement our analysis with proper motions based on both the VVV and Gaia Data Release 2. Results. We derive an empirical K s -band PL relation that depends on Galactic longitude and latitude: K s 0 = (10.66 ± 0.02) − (2.21 ± 0.03)·(log P −1.2)−(0.020±0.003)· l +(0.050±0.008)·| b | mag in idual extinction corrections are based on a 3D reddening map. Our targets display a centrally concentrated distribution, with solid evidence of ellipsoidal symmetry – similar to the RR Lyræ ellipsoid – and a few halo outliers up to ≳100 kpc. We obtain a distance from the Galactic center of R 0 = 8.46 ± 0.03(stat.) ± 0.11(syst.) kpc. We also find evidence that the bulge T2Cs belong to a kinematically hot population, as the tangential velocity components ( συ l ∗ = 104.2 ± 3.0kms −1 and συ b = 96.8 ± 5.5kms −1 ) agree within 1.2 σ . Moreover, the difference between absolute and relative proper motion is in good agreement with the proper motion of Sgr A ✻ from VLBA measures. Conclusions. We conclude that bulge T2Cs display an ellipsoidal spatial distribution and have kinematics similar to RR Lyræ stars, which are other tracers of the old, low-mass stellar population. T2Cs also provide an estimate of R 0 that agrees excellently well with the literature, taking account of the reddening law.
Publisher: IOP Publishing
Date: 29-11-2016
Publisher: Cambridge University Press (CUP)
Date: 08-2009
Publisher: EDP Sciences
Date: 17-01-2008
Publisher: American Astronomical Society
Date: 08-10-2019
Publisher: Oxford University Press (OUP)
Date: 11-10-1998
Publisher: American Astronomical Society
Date: 09-05-2019
Publisher: Cambridge University Press (CUP)
Date: 08-2009
DOI: 10.1017/S174392130999086X
Abstract: In spite of significant recent and ongoing research efforts, most of the early evolution and long-term fate of young massive star clusters remain clouded in uncertainties. Here, I discuss our understanding of the initial conditions of star cluster formation and the importance of initial substructure for the subsequent dynamical-evolution and mass-segregation timescales. I also assess our current understanding of the (initial) binary fraction in star clusters and the shape of the stellar initial mass function at the low-mass end in the low-metallicity environment of the Large Magellanic Cloud. Finally, I question the validity of our assumptions leading to dynamical cluster mass estimates. I conclude that it seems imperative that observers, modellers and theorists combine efforts and exchange ideas and data freely for the field to make a major leap forward.
Publisher: Cambridge University Press (CUP)
Date: 08-2012
DOI: 10.1017/S1743921312021709
Abstract: Knowing the distance of an astrophysical object is key to understanding it. However, at present, comparisons of theory and observations are h ered by precision (or lack thereof) in distance measurements or estimates. Putting the many recent results and new developments into the broader context of the physics driving cosmic distance determination is the next logical step, which will benefit from the combined efforts of theorists, observers and modellers working on a large variety of spatial scales, and spanning a wide range of expertise. IAU Symposium 289 addressed the physics underlying methods of distance determination across the Universe, exploring the various approaches employed to define the milestones along the road. The meeting provided an exciting snapshot of the field of distance measurement, offering not only up-to-date results and a cutting-edge account of recent progress, but also full discussion of the pitfalls encountered and the uncertainties that remain. One of the meeting's main aims was to provide a roadmap for future efforts in this field, both theoretically and observationally.
Publisher: Springer Science and Business Media LLC
Date: 08-2018
Publisher: Cambridge University Press (CUP)
Date: 10-2007
DOI: 10.1017/S1743921308019856
Abstract: We derived proper motions and membership probabilities of stars in the regions of two very young (~ 2–4 Myr-old) open clusters NGC 2244 and NGC 6530. Both clusters show clear evidence of mass segregation, which provides strong support for the suggestion that the observed mass segregation is – at least partially – due to the way in which star formation has proceeded in these complex star-forming regions (“primordial” mass segregation).
Publisher: Oxford University Press (OUP)
Date: 21-03-2007
Publisher: Oxford University Press (OUP)
Date: 21-11-2008
Publisher: American Astronomical Society
Date: 04-11-2010
Publisher: Oxford University Press (OUP)
Date: 21-08-2003
Publisher: American Astronomical Society
Date: 27-10-2020
Publisher: EDP Sciences
Date: 27-10-2008
Publisher: Springer Netherlands
Date: 2005
Publisher: Oxford University Press (OUP)
Date: 21-12-2007
Publisher: Cambridge University Press (CUP)
Date: 08-2013
DOI: 10.1017/S1743921315005591
Abstract: The business session for Commission 37 was held on 24 August 2012 at the IAU General Assembly in Beijing. The meeting was attended by about a dozen members of our Comission, including President Carraro, VP de Grijs and several committee members. We introduced ourselves and then went through a powerpoint presentation first prepared by outgoing President Elmegreen and revised by incoming President Carraro. The contents of the powerpoint presentation are given in this summary.
Publisher: Oxford University Press (OUP)
Date: 27-09-2017
Publisher: Oxford University Press (OUP)
Date: 12-12-2007
Publisher: Oxford University Press (OUP)
Date: 11-06-2003
Publisher: American Astronomical Society
Date: 06-05-2019
Publisher: BMJ
Date: 10-07-2014
DOI: 10.1136/BMJ.G4164
Publisher: American Astronomical Society
Date: 30-04-2021
Publisher: American Astronomical Society
Date: 08-05-2019
Publisher: American Astronomical Society
Date: 23-05-2013
Publisher: Oxford University Press (OUP)
Date: 14-04-2022
Abstract: We present proper motion (PM) measurements within the central region of the Large Magellanic Cloud (LMC), using near-infrared data from the VISTA survey of the Magellanic Cloud system (VMC). This work encompasses 18 VMC tiles covering a total sky area of ∼28 deg2. We computed absolute stellar PMs from multiepoch observations in the Ks filter over time baselines between ∼12 and 47 months. Our final catalogue contains ∼6322 000 likely LMC member stars with derived PMs. We employed a simple flat-rotating disc model to analyse and interpret the PM data. We found a stellar centre of rotation ($\\alpha _{0} = 79.95^{\\circ }\\,^{+0.22}_{-0.23}$, $\\delta _0 = -69.31^{\\circ }\\,^{+0.12}_{-0.11}$) that is in agreement with that resulting from Hubble Space Telescope data. The inferred viewing angles of the LMC disc ($i=33.5^{\\circ }\\,^{+1.2}_{-1.3}$, $\\Theta =129.8^{\\circ }\\,^{+1.9}_{-1.9}$) are in good agreement with values from the literature but suggest a higher inclination of the central parts of the LMC. Our data confirm a higher rotation litude for the young (≲0.5 Gyr) stars compared to the intermediate-age/old (≳1 Gyr) population, which can be explained by asymmetric drift. We constructed spatially resolved velocity maps of the intermediate-age/old and young populations. Intermediate-age/old stars follow elongated orbits parallel to the bar’s major axis, providing first observational evidence for x1 orbits within the LMC bar. In the innermost regions, the motions show more chaotic structures. Young stars show motions along a central filamentary bar structure.
Publisher: Springer Netherlands
Date: 2003
Publisher: China Science Publishing & Media Ltd.
Date: 03-2023
Publisher: EDP Sciences
Date: 2013
Publisher: Elsevier BV
Date: 06-2006
Publisher: American Astronomical Society
Date: 30-06-2014
Publisher: Oxford University Press (OUP)
Date: 04-05-2023
Abstract: We present a kinematic analysis of the Small Magellanic Cloud using 3700 spectra extracted from the European Southern Observatory archive. We used data from Gaia and near-infrared photometry to select stellar populations and discard Galactic foreground stars. The s le includes main-sequence red giant branch and red clump stars, observed with Fibre Large Array Multi Wavelength Spectrograph. The spectra have a resolving power λ/Δλ from 6500 to 38 000. We derive radial velocities by employing a full spectrum fitting method using a penalized pixel fitting routine. We obtain a mean radial velocity for the galaxy of 159 ± 2 km s−1, with a velocity dispersion of 33 ± 2 km s−1. Our velocities agree with literature estimates for similar (young or old) stellar populations. The radial velocity of stars in the Wing and bar-like structures differ as a consequence of the dynamical interaction with the Large Magellanic Cloud. The higher radial velocity of young main-sequence stars in the bar compared to that of supergiants can be attributed to star formation around 40 Myr ago from gas already influenced by tidal stripping. Similarly, young main-sequence stars in the northern part of the bar, resulting from a prominent star forming episode 25 Myr ago, have a higher radial velocity than stars in the southern part. Radial velocity differences between the northern and southern bar overdensities are also traced by giant stars. They are corroborated by studies of the cold gas and proper motion indicating stretching/tidal stripping of the galaxy.
Publisher: American Astronomical Society
Date: 23-03-2020
Publisher: American Astronomical Society
Date: 12-2021
Abstract: Observing nearby galaxies with submillimeter telescopes on the ground has two major challenges. First, the brightness is significantly reduced at long submillimeter wavelengths compared to the brightness at the peak of the dust emission. Second, it is necessary to use a high-pass spatial filter to remove atmospheric noise on large angular scales, which has the unwelcome side effect of also removing the galaxy’s large-scale structure. We have developed a technique for producing high-resolution submillimeter images of galaxies of large angular size by using the telescope on the ground to determine the small-scale structure (the large Fourier components) and a space telescope (Herschel or Planck) to determine the large-scale structure (the small Fourier components). Using this technique, we are carrying out the HARP and SCUBA-2 High Resolution Terahertz Andromeda Galaxy Survey (HASHTAG), an international Large Program on the James Clerk Maxwell Telescope, with one aim being to produce the first high-fidelity high-resolution submillimeter images of Andromeda. In this paper, we describe the survey, the method we have developed for combining the space-based and ground-based data, and we present the first HASHTAG images of Andromeda at 450 and 850 μ m. We also have created a method to predict the CO( J = 3–2) line flux across M31, which contaminates the 850 μ m band. We find that while normally the contamination is below our sensitivity limit, it can be significant (up to 28%) in a few of the brightest regions of the 10 kpc ring. We therefore also provide images with the predicted line emission removed.
Publisher: American Astronomical Society
Date: 09-08-2007
DOI: 10.1086/521022
Publisher: Springer Science and Business Media LLC
Date: 12-2014
DOI: 10.1038/NATURE13969
Abstract: Stars spend most of their lifetimes on the main sequence in the Hertzsprung-Russell diagram. The extended main-sequence turn-off regions--containing stars leaving the main sequence after having spent all of the hydrogen in their cores--found in massive (more than a few tens of thousands of solar masses), intermediate-age (about one to three billion years old) star clusters are usually interpreted as evidence of internal age spreads of more than 300 million years, although young clusters are thought to quickly lose any remaining star-forming fuel following a period of rapid gas expulsion on timescales of order 10(7) years. Here we report, on the basis of a combination of high-resolution imaging observations and theoretical modelling, that the stars beyond the main sequence in the two-billion-year-old cluster NGC 1651, characterized by a mass of about 1.7 × 10(5) solar masses, can be explained only by a single-age stellar population, even though the cluster has a clearly extended main-sequence turn-off region. The most plausible explanation for the existence of such extended regions invokes a population of rapidly rotating stars, although the secondary effects of the prolonged stellar lifetimes associated with such a stellar population mixture are as yet poorly understood. From preliminary analysis of previously obtained data, we find that similar morphologies are apparent in the Hertzsprung-Russell diagrams of at least five additional intermediate-age star clusters, suggesting that an extended main-sequence turn-off region does not necessarily imply the presence of a significant internal age dispersion.
Publisher: Cambridge University Press (CUP)
Date: 08-2006
DOI: 10.1017/S1743921306005035
Abstract: I assess the similarities and differences between the star-formation modes in quiescent spiral galaxies versus those in violent starburst regions, including galactic nuclei. As opposed to the quiescent star-formation mode, current empirical evidence on the star-formation processes in the extreme, high-pressure environments induced by galaxy encounters strongly suggests that star cluster formation is an important and perhaps even the dominant mode of star formation in such starburst events. This implies that by using star clusters as unique diagnostic probes, we can trace a galaxy's most violent star formation history very well, at least for the past few Gyr. The sizes, luminosities, and mass estimates of the young massive star clusters are entirely consistent with what is expected for young Milky Way-type globular clusters (GCs). Recent evidence lends support to the scenario that GCs, which were once thought to be the oldest building blocks of galaxies, are still forming today.
Publisher: Cambridge University Press (CUP)
Date: 08-2006
DOI: 10.1017/S1743921307005388
Abstract: At the centre of the Milky Way is Sgr A*, a putative 3 million solar mass black hole with an observed luminosity that is orders of magnitude smaller than that expected from simple accretion theories. The number density of early-type stars is quite high near Sgr A*, so the ensemble of their stellar winds has a significant impact on the black hole's environment. We present results of 3D hydrodynamic simulations of the accretion of stellar winds onto Sgr A*. Using the LANL/SAIC code, RAGE, we model the central arc-second of the Galaxy, including the central cluster stars (the S-stars) with orbits and wind parameters that match observations. A significant fraction of the winds from the S stars becomes gravitationally bound to the black hole and thus could provide enough hot gas to produce the X-ray emission seen by Chandra. We perform radiative transfer calculations on the 3D hydrodynamic data cubes and present the resulting synthetic X-ray spectrum.
Publisher: EDP Sciences
Date: 07-2014
Publisher: Oxford University Press (OUP)
Date: 02-2008
Publisher: American Astronomical Society
Date: 27-09-2022
Abstract: Multimode Cepheids pulsate simultaneously in more than one mode of oscillation. They provide an independent means to test stellar models and pulsation theories. They can also be used to derive metallicities. In recent years, the number of known multimode Cepheids has increased dramatically with the discovery of a large number of Galactic double-mode Cepheids. To date, 209 double-mode Cepheids have been detected in the Galactic bulge and disk, mostly based on the Optical Gravitational Lensing Experiment’s (OGLE) catalog. In this paper, we conduct a comprehensive search for double-mode Cepheids in the northern sky based on Zwicky Transient Facility Data Release 5. We found 72 such objects in the Milky Way. The periods of the 30 s le objects already included in the OGLE catalog show excellent agreement with the OGLE periods. The period ratios of our new Cepheids are consistent with those of known double-mode Cepheids, as evidenced by their loci in the so-called “Petersen diagram.” Compared with OGLE, the completeness of our double-mode Cepheid s le is around 71%. The much improved temporal s ling of the Zwicky Transient Facility offers significant scope to find more double-mode Cepheids, especially at the distribution’s short-period end.
Publisher: Springer Netherlands
Date: 2005
Publisher: American Medical Association (AMA)
Date: 06-2015
Publisher: Oxford University Press (OUP)
Date: 22-03-2013
DOI: 10.1093/MNRAS/STT392
Publisher: Cambridge University Press (CUP)
Date: 10-2007
DOI: 10.1017/S1743921308019765
Abstract: We review our work on Galactic open clusters in recent years, and introduce our proposed large program for the LOCS (LAMOST Open Cluster Survey). First, based on the most complete open clusters s le with metallicity, age and distance data as well as kinematic information, some preliminary statistical analysis regarding the spatial and metallicity distributions is presented. In particular, a radial abundance gradient of −0.058±0.006 dex kpc −1 is derived. By iding clusters into the age groups we show that the disk abundance gradient was steeper in the past. Secondly, proper motions, membership probabilities, and velocity dispersions of stars in the regions of two very young open clusters are derived. Both clusters show clear evidence of mass segregation, which provides support for the “primordial” mass segregation scenario. Based on the advantages of the forthcoming LAMOST facility, we have proposed a detailed open cluster survey with LAMOST (the LOCS). The aim, feasibility, and the present development of the LOCS are briefly summarized.
Publisher: EDP Sciences
Date: 2003
DOI: 10.1051/EAS:2003023
Publisher: EDP Sciences
Date: 09-2020
DOI: 10.1051/0004-6361/202037478
Abstract: Context. The Magellanic Clouds are a nearby pair of interacting dwarf galaxies and satellites of the Milky Way. Studying their kinematic properties is essential to understanding their origin and dynamical evolution. They have prominent tidal features and the kinematics of these features can give hints about the formation of tidal dwarfs, galaxy merging and the stripping of gas. In addition they are an ex le of dwarf galaxies that are in the process of merging with a massive galaxy. Aims. The goal of this study is to investigate the kinematics of the Magellanic Bridge, a tidal feature connecting the Magellanic Clouds, using stellar proper motions to understand their most recent interaction. Methods. We calculated proper motions based on multi-epoch K s -band aperture photometry, which were obtained with the Visible and Infrared Survey Telescope for Astronomy (VISTA), spanning a time of 1−3 yr, and we compared them with Gaia Data Release 2 (DR2) proper motions. We tested two methods for removing Milky Way foreground stars using Gaia DR2 parallaxes in combination with VISTA photometry or using distances based on Bayesian inference. Results. We obtained proper motions for a total of 576 411 unique sources over an area of 23 deg 2 covering the Magellanic Bridge including mainly Milky Way foreground stars, background galaxies, and a small population of possible Magellanic Bridge stars ( 15 000), which mostly consist of giant stars with 11.0 K s 19.5 mag. The first proper motion measurement of the Magellanic Bridge centre is 1.80 ± 0.25 mas yr −1 in right ascension and −0.72 ± 0.13 mas yr −1 in declination. The proper motion measurements of stars along the Magellanic Bridge from the VISTA survey of the Magellanic Cloud system (VMC) and Gaia DR2 data confirm a flow motion from the Small to the Large Magellanic Cloud. This flow can now be measured all across the entire length of the Magellanic Bridge. Conclusions. Our measurements indicate that the Magellanic Bridge is stretching. By converting the proper motions to tangential velocities, we obtain ∼110 km s −1 in the plane of the sky. Therefore it would take a star roughly 177 Myr to cross the Magellanic Bridge.
Publisher: Oxford University Press (OUP)
Date: 24-03-2020
Abstract: To study the high-transition dense-gas tracers and their relationships to the star formation of the inner ∼2 kpc circumnuclear region of NGC 253, we present HCN J = 4−3 and HCO+ J = 4−3 maps obtained with the James Clerk Maxwell Telescope. Using the spatially resolved data, we compute the concentration indices r90/r50 for the different tracers. HCN and HCO+ 4–3 emission features tend to be centrally concentrated, which is in contrast to the shallower distribution of CO 1–0 and the stellar component. The dense-gas fraction (fdense, traced by the velocity-integrated-intensity ratios of HCN/CO and HCO+/CO) and the ratio R31 (CO 3–2/1–0) decline towards larger galactocentric distances, but increase with higher star formation rate surface density. The radial variation and the large scatter of fdense and R31 imply distinct physical conditions in different regions of the galactic disc. The relationships of fdense versus Σstellar, and SFEdense versus Σstellar are explored. SFEdense increases with higher Σstellar in this galaxy, which is inconsistent with previous work that used HCN 1–0 data. This implies that existing stellar components might have different effects on the high-J HCN and HCO+ than their low-J emission. We also find that SFEdense seems to be decreasing with higher fdense which is consistent with previous works, and it suggests that the ability of the dense gas to form stars diminishes when the average density of the gas increases. This is expected in a scenario where only the regions with high-density contrast collapse and form stars.
Publisher: Wiley
Date: 02-2004
Publisher: American Astronomical Society
Date: 07-02-2013
Publisher: Oxford University Press (OUP)
Date: 18-08-2017
Publisher: Oxford University Press (OUP)
Date: 10-07-2012
Publisher: Springer Science and Business Media LLC
Date: 23-12-2015
Publisher: Springer Science and Business Media LLC
Date: 22-09-2009
Publisher: Elsevier BV
Date: 2006
Publisher: Oxford University Press (OUP)
Date: 2004
Publisher: American Astronomical Society
Date: 10-2017
Abstract: As part of an extensive data mining effort, we have compiled a database of 162 Galactic rotation speed measurements at R 0 (the solar Galactocentric distance), . Published between 1927 and 2017 June, this represents the most comprehensive set of values since the 1985 meta-analysis that led to the last revision of the International Astronomical Union’s recommended Galactic rotation constants. Although we do not find any compelling evidence for the presence of “publication bias” in recent decades, we find clear differences among the values and the ratios resulting from the use of different tracer populations. Specifically, young tracers (including OB and supergiant stars, masers, Cepheid variables, H ii regions, and young open clusters), as well as kinematic measurements of Sgr A* near the Galactic Center, imply a significantly larger Galactic rotation speed at the solar circle and a higher ratio (i.e., km s −1 and km s −1 kpc −1 statistical uncertainties only) than any of the tracers dominating the Galaxy’s mass budget (i.e., field stars and the H i /CO distributions). Using the latter to be most representative of the bulk of the Galaxy’s matter distribution, we arrive at an updated set of Galactic rotation constants,
Publisher: Cambridge University Press (CUP)
Date: 08-1970
Publisher: EDP Sciences
Date: 28-01-2016
Publisher: American Astronomical Society
Date: 10-09-2007
DOI: 10.1086/522120
Publisher: American Astronomical Society
Date: 08-2018
Publisher: Oxford University Press (OUP)
Date: 03-07-2012
Publisher: Springer Science and Business Media LLC
Date: 11-02-2015
DOI: 10.1038/NATURE14132
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
Start Date: 2006
End Date: 2008
Funder: Engineering and Physical Sciences Research Council
View Funded ActivityStart Date: 2006
End Date: 2009
Funder: Science and Technology Facilities Council
View Funded ActivityStart Date: 2007
End Date: 2007
Funder: Royal Society
View Funded ActivityStart Date: 2006
End Date: 2009
Funder: Science and Technology Facilities Council
View Funded ActivityStart Date: 2009
End Date: 2012
Funder: Science and Technology Facilities Council
View Funded ActivityStart Date: 2006
End Date: 2008
Funder: Engineering and Physical Sciences Research Council
View Funded ActivityStart Date: 2019
End Date: 2019
Funder: Australian Research Council
View Funded ActivityStart Date: 07-2019
End Date: 05-2022
Amount: $500,000.00
Funder: Australian Research Council
View Funded Activity