ORCID Profile
0000-0003-2688-7511
Current Organisation
Australian National University
Does something not look right? The information on this page has been harvested from data sources that may not be up to date. We continue to work with information providers to improve coverage and quality. To report an issue, use the Feedback Form.
In Research Link Australia (RLA), "Research Topics" refer to ANZSRC FOR and SEO codes. These topics are either sourced from ANZSRC FOR and SEO codes listed in researchers' related grants or generated by a large language model (LLM) based on their publications.
Stellar Astronomy and Planetary Systems | Astronomical and Space Sciences | Galactic Astronomy | Cosmology and Extragalactic Astronomy | Astronomical and Space Instrumentation
Expanding Knowledge in the Physical Sciences | Scientific Instruments |
Publisher: EDP Sciences
Date: 13-04-2016
Publisher: Cambridge University Press (CUP)
Date: 08-2009
DOI: 10.1017/S1743921310000220
Abstract: We present Li abundances for 73 stars in the metallicity range −3.5 [Fe/H] −1.0 using improved IRFM temperatures (Casagrande et al . 2009) with precise E(B-V) values obtained mostly from interstellar NaI D lines, and high-quality equivalent widths (σ EW ~ 3%). At all metallicities we uncover a fine-structure in the Li abundances of Spite plateau stars, which we trace to Li depletion that depends on both metallicity and mass. Models including atomic diffusion and turbulent mixing seem to reproduce the observed Li depletion assuming a primordial Li abundance A Li = 2.64 dex (MARCS models) or 2.72 (Kurucz overshooting models), in good agreement with current predictions ( A Li = 2.72) from standard BBN.
Publisher: Oxford University Press (OUP)
Date: 11-09-2008
Publisher: EDP Sciences
Date: 11-2018
DOI: 10.1051/0004-6361/201629294
Abstract: Context . It is well known that the magnetic activity of solar-type stars decreases with age, but it is widely debated in the literature whether there is a smooth decline or if there is an early sharp drop until 1–2 Gyr that is followed by a relatively inactive constant phase. Aims . We revisited the activity-age relation using time-series observations of a large s le of solar twins whose precise isochronal ages and other important physical parameters have been determined. Methods . We measured the Ca II H and K activity indices using ≈9000 HARPS spectra of 82 solar twins. In addition, the average solar activity was calculated through asteroids and Moon reflection spectra using the same instrumentation. Thus, we transformed our activity indices into the S Mount Wilson scale ( S MW ), recalibrated the Mount Wilson absolute flux and photospheric correction equations as a function of T eff , and then computed an improved bolometric flux normalized activity index log R ′ HK ( T eff ) for the entire s le. Results . New relations between activity and the age of solar twins were derived by assessing the chromospheric age-dating limits using log R ′ HK ( T eff ). We measured an average solar activity of S MW = 0.1712 ± 0.0017 during solar magnetic cycles 23–24 covered by HARPS observations, and we also inferred an average of S MW = 0.1694 ± 0.0025 for cycles 10–24, anchored on a sunspot number correlation of S index versus. We also found a simple relation between the average and the dispersion of the activity levels of solar twins. This enabled us to predict the stellar variability effects on the age-activity diagram, and consequently, to estimate the chromospheric age uncertainties that are due to the same phenomena. The age-activity relation is still statistically significant up to ages around 6–7 Gyr, in agreement with previous works using open clusters and field stars with precise ages. Conclusions . Our research confirms that Ca II H & K lines remain a useful chromospheric evolution tracer until stars reach ages of at least 6–7 Gyr. We found evidence that for the most homogenous set of old stars, the chromospheric activity indices seem to continue to decrease after the solar age toward the end of the main sequence. Our results indicate that a significant part of the scatter observed in the age-activity relation of solar twins can be attributed to stellar cycle modulations effects. The Sun seems to have a normal activity level and variability for its age.
Publisher: Oxford University Press (OUP)
Date: 11-2022
Abstract: Hubble Space Telescope (HST) photometry is providing an extensive analysis of globular clusters (GCs). In particular, the pseudo-two-colour diagram dubbed 'chromosome map (ChM)’ allowed to detect and characterize their multiple populations with unprecedented detail. The main limitation of these studies is the small field of view of HST, which makes it challenging to investigate some important aspects of the multiple populations, such as their spatial distributions and the internal kinematics in the outermost cluster regions. To overcome this limitation, we analyse state-of-art wide-field photometry of 43 GCs obtained from ground-based facilities. We derived high-resolution reddening maps and corrected the photometry for differential reddening when needed. We use photometry in the U, B, and I bands to introduce the ΔcU, B, I versus ΔB, I ChM of red-giant branch (RGB) and asymptotic-giant branch stars. We demonstrate that this ChM, which is built with wide-band ground-based photometry, is an efficient tool to identify first- and second-generation stars (1G and 2G) over a wide field of view. To illustrate its potential, we derive the radial distribution of multiple populations in NGC 288 and infer their chemical composition. We present the ChMs of RGB stars in 29 GCs and detect a significant degree of variety. The fraction of 1G and 2G stars, the number of subpopulations, and the extension of the ChMs significantly change from one cluster to another. Moreover, the metal-poor and metal-rich stars of Type II GCs define distinct sequences in the ChM. We confirm the presence of extended 1G sequences.
Publisher: Oxford University Press (OUP)
Date: 03-03-2020
Abstract: In the current era of Gaia and large, high signal-to-noise stellar spectroscopic surveys, there is an unmet need for a reliable library of fundamentally calibrated stellar effective temperatures based on accurate stellar diameters. Here, we present a set of precision diameters and temperatures for a s le of 6 dwarf, 5 sub-giant, and 5 giant stars observed with the PIONIER beam combiner at the VLTI. Science targets were observed in at least two sequences with five unique calibration stars each for accurate visibility calibration and to reduce the impact of bad calibrators. We use the standard PIONIER data reduction pipeline, but bootstrap over interferograms, in addition to employing a Monte Carlo approach to account for correlated errors by s ling stellar parameters, limb darkening coefficients, and fluxes, as well as predicted calibrator angular diameters. The resulting diameters were then combined with bolometric fluxes derived from broad-band Hipparcos–Tycho photometry and MARCS model bolometric corrections, plus parallaxes from Gaia to produce effective temperatures, physical radii, and luminosities for each star observed. Our stars have mean angular diameter and temperatures uncertainties of 0.8 per cent and 0.9 per cent, respectively, with our s le including diameters for 10 stars with no pre-existing interferometric measurements. The remaining stars are consistent with previous measurements, with the exception of a single star which we observe here with PIONIER at both higher resolution and greater sensitivity than was achieved in earlier work.
Publisher: EDP Sciences
Date: 06-2020
DOI: 10.1051/0004-6361/202037923
Abstract: Context. The HR 1614 is an overdensity in velocity space and has for a long time been known as an old (∼2 Gyr) and metal-rich ([Fe/H] ≈ +0.2) nearby moving group that has a dissolving open cluster origin. The existence of such old and metal-rich groups in the solar vicinity is quite unexpected since the vast majority of nearby moving groups are known to be young. Aims. In the light of new and significantly larger data sets than ever before (astrometric, photometric, and spectroscopic), we aim to re-investigate the properties and origin of the HR 1614 moving group. If the HR 1614 overdensity is a dissolving cluster, its stars should represent a single-age and single-elemental abundance population. Methods. To identify and characterise the HR 1614 moving group we use astrometric data from Gaia DR2 distances, extinction, and reddening corrections from the StarHorse code elemental abundances from the GALAH and APOGEE spectroscopic surveys and photometric metallicities from the SkyMapper survey. Bayesian ages were estimated for the SkyMapper stars. Since the Hercules stream is the closest kinematical structure to the HR 1614 moving group in velocity space and as its origin is believed to be well-understood, we use the Hercules stream for comparison purposes. Stars that are likely to be members of the two groups were selected based on their space velocities. Results. The HR 1614 moving group is located mainly at negative U velocities, does not form an arch of constant energy in the U − V space, and is tilted in V . We find that the HR 1614 overdensity is not chemically homogeneous, but that its stars exist at a wide range of metallicities, ages, and elemental abundance ratios. They are essentially similar to what is observed in the Galactic thin and thick discs, a younger population (around 3 Gyr) that is metal-rich (−0.2 ≤ [Fe/H] ≤ 0.4) and alpha-poor. These findings are very similar to what is seen for the Hercules stream, which is believed to have a dynamical origin and consists of regular stars from the Galactic discs. Conclusions. The HR 1614 overdensity has a wide spread in metallicity, [Mg/Fe], and age distributions resembling the general properties of the Galactic disc. It should therefore not be considered a dissolving open cluster, or an accreted population. Based on the kinematic and chemical properties of the HR 1614 overdensity we suggest that it has a complex origin that could be explained by combining several different mechanisms such as resonances with the Galactic bar and spiral structure, phase mixing of dissolving spiral structure, and phase mixing due to an external perturbation.
Publisher: Oxford University Press (OUP)
Date: 14-01-2021
Abstract: The NASA Transiting Exoplanet Survey Satellite (NASA-TESS) mission presents a treasure trove for understanding the stars it observes and the Milky Way, in which they reside. We present a first look at the prospects for Galactic and stellar astrophysics by performing initial asteroseismic analyses of bright (G & 11) red giant stars in the TESS southern continuous viewing zone (SCVZ). Using three independent pipelines, we detect νmax and Δν in 41 per cent of the 15 405 star parent s le (6388 stars), with consistency at a level of $\\sim \\! 2{{\\ \\rm per\\ cent}}$ in νmax and $\\sim \\! 5{{\\ \\rm per\\ cent}}$ in Δν. Based on this, we predict that seismology will be attainable for ∼3 × 105 giants across the whole sky and at least 104 giants with ≥1 yr of observations in the TESS-CVZs, subject to improvements in analysis and data reduction techniques. The best quality TESS-CVZ data, for 5574 stars where pipelines returned consistent results, provide high-quality power spectra across a number of stellar evolutionary states. This makes possible studies of, for ex le, the asymptotic giant branch bump. Furthermore, we demonstrate that mixed ℓ = 1 modes and rotational splitting are cleanly observed in the 1-yr data set. By combining TESS-CVZ data with TESS-HERMES, SkyMapper, APOGEE, and Gaia, we demonstrate its strong potential for Galactic archaeology studies, providing good age precision and accuracy that reproduces well the age of high [α/Fe] stars and relationships between mass and kinematics from previous studies based on e.g. Kepler. Better quality astrometry and simpler target selection than the Kepler s le makes this data ideal for studies of the local star formation history and evolution of the Galactic disc. These results provide a strong case for detailed spectroscopic follow-up in the CVZs to complement that which has been (or will be) collected by current surveys.
Publisher: Oxford University Press (OUP)
Date: 06-09-2017
Publisher: American Astronomical Society
Date: 25-11-2019
Publisher: American Astronomical Society
Date: 04-2021
Abstract: The zero point of the reddening toward the Large Magellanic Cloud (LMC) has been the subject of some dispute. Its uncertainty propagates as a systematic error for methods that measure the extragalactic distance scale through knowledge of the absolute extinction of LMC stars. In an effort to resolve this issue, we used three different methods to calibrate the most widely used metric to predict LMC extinction, the intrinsic color of the red clump, ( V − I ) RC ,0 , for the inner ∼3° of that galaxy. The first approach was to empirically calibrate the color zero points of the BaSTI isochrones over a wide metallicity range of Δ[Fe/H] ≈ 1.10 using measurements of red clump stars in 47 Tuc, the solar neighborhood, and NGC 6791. From these efforts, we also measure these properties of the solar neighborhood red clump, ( V − I , G BP − K s , G − K s , G RP − K s , J − K s , H − K s , M I , M Ks ) RC ,0 = (1.02, 2.75, 2.18, 1.52, 0.64, 0.15, −0.23, −1.63). The second and third methods were to compare the observed colors of the red clump to those of Cepheids and RR Lyrae in the LMC. With these three methods, we estimated the intrinsic color of the red clump of the LMC to be ( V − I ) RC ,0,LMC = {≈ 0.93 , 0.91 ± 0.02, 0.89 ± 0.02}, respectively, and similarly, using the first and third methods, we estimated ( V − I ) RC ,0,SMC = {≈ 0.85 , 0.84 ± 0.02}, respectively, for the Small Magellanic Cloud. We estimate the luminosities to be M I , RC ,LMC = −0.26 and M I , RC ,SMC = −0.37. We show that this has important implications for recent calibrations of the tip of the red giant branch in the Magellanic Clouds used to measure H 0 .
Publisher: Oxford University Press (OUP)
Date: 07-11-2015
Publisher: Oxford University Press (OUP)
Date: 21-11-2006
Publisher: Oxford University Press (OUP)
Date: 11-10-2021
Abstract: We introduce the public version of the BAyesian STellar Algorithm (BASTA), an open-source code written in Python to determine stellar properties based on a set of astrophysical observables. BASTA has been specifically designed to robustly combine large data sets that include asteroseismology, spectroscopy, photometry, and astrometry. We describe the large number of asteroseismic observations that can be fit by the code and how these can be combined with atmospheric properties (as well as parallaxes and apparent magnitudes), making it the most complete analysis pipeline available for oscillating main-sequence, subgiant, and red giant stars. BASTA relies on a set of pre-built stellar isochrones or a custom-designed library of stellar tracks, which can be further refined using our interpolation method (both along and across stellar tracks or isochrones). We perform recovery tests with simulated data that reveal levels of accuracy at the few percent level for radii, masses, and ages when in idual oscillation frequencies are considered, and show that asteroseismic ages with statistical uncertainties below 10 per cent are within reach if our stellar models are reliable representations of stars. BASTAis extensively documented and includes a suite of ex les to support easy adoption and further development by new users.
Publisher: Oxford University Press (OUP)
Date: 31-12-2015
Publisher: Oxford University Press (OUP)
Date: 29-11-2012
DOI: 10.1093/MNRAS/STS319
Publisher: American Astronomical Society
Date: 04-05-2017
Publisher: American Astronomical Society
Date: 14-07-2015
Publisher: Oxford University Press (OUP)
Date: 04-2015
DOI: 10.1093/MNRAS/STV420
Publisher: IEEE
Date: 07-2013
Publisher: Oxford University Press (OUP)
Date: 18-04-2018
DOI: 10.1093/MNRAS/STY898
Publisher: American Astronomical Society
Date: 19-09-2018
Publisher: Cambridge University Press (CUP)
Date: 11-2010
DOI: 10.1017/S1743921310003960
Abstract: For nearby K dwarfs, the broadening of the observed Main Sequence at low metallicities is much narrower than expected from isochrones with the standard helium–to–metal enrichment ratio Δ Y /Δ Z ~2. A much higher value, of order 10, is formally needed to reproduce the observed broadening, but it returns helium abundances in awkward contrast with Big Bang Nucleosynthesis. This steep enrichment ratio resembles, on a milder scale, the very high Δ Y /Δ Z estimated from the multiple Main Sequences observed in some metal-poor Globular Clusters. We argue that a revision of low Main Sequence stellar models, suggested from nearby stars, could help to reduce the overwhelmingly high Δ Y /Δ Z deduced so far for those clusters. Under the most favourable assumptions, the estimated helium content for the enriched populations may decrease from Y ≃ 0.4 to as low as Y ≃ 0.3, with intermediate values being plausible.
Publisher: Oxford University Press (OUP)
Date: 21-12-2020
Abstract: Statistical studies of exoplanets and the properties of their host stars have been critical to informing models of planet formation. Numerous trends have arisen in particular from the rich Kepler data set, including that exoplanets are more likely to be found around stars with a high metallicity and the presence of a ‘gap’ in the distribution of planetary radii at 1.9 R⊕. Here we present a new analysis on the Kepler field, using the APOGEE spectroscopic survey to build a metallicity calibration based on Gaia, 2MASS and Strömgren photometry. This calibration, along with masses and radii derived from a Bayesian isochrone fitting algorithm, is used to test a number of these trends with unbiased, photometrically derived parameters, albeit with a smaller s le size in comparison to recent studies. We recover that planets are more frequently found around higher metallicity stars over the entire s le, planetary frequencies are 0.88 ± 0.12 per cent for [Fe/H] & 0 and 1.37 ± 0.16 per cent for [Fe/H] ≥ 0 but at two sigma we find that the size of exoplanets influences the strength of this trend. We also recover the planet radius gap, along with a slight positive correlation with stellar mass. We conclude that this method shows promise to derive robust statistics of exoplanets. We also remark that spectrophotometry from Gaia DR3 will have an effective resolution similar to narrow band filters and allow to overcome the small s le size inherent in this study.
Publisher: American Astronomical Society
Date: 31-10-2012
Publisher: Wiley
Date: 09-2016
Abstract: Setting the timeline of the events which shaped the Milky Way disc through its 13 billion year old history is one of the major challenges in the theory of galaxy formation. Achieving this goal is possible using late‐type stars, which in virtue of their long lifetimes can be regarded as fossil remnants from various epochs of the formation of the Galaxy. There are two main paths to reliably age‐date late‐type stars: astrometric distances for stars in the turn‐off and subgiant region, or oscillation frequencies along the red giant branch. So far, these methods have been applied to large s les of stars in the solar neighbourhood, and in the Kepler field. I review these studies, emphasize how they complement each other, and highlight some of the constraints they provide for Galactic modelling. I conclude with the prospects and synergies that astrometric (Gaia) and asteroseismic space‐borne missions reserve to the field of Galactic archaeology, and advocate that survey selection functions should be kept as simple as possible, relying on basic observables such as colours and magnitudes only.
Publisher: Oxford University Press (OUP)
Date: 25-09-2018
Publisher: EDP Sciences
Date: 04-2019
DOI: 10.1051/0004-6361/201833218
Abstract: The overlap between the spectroscopic Galactic Archaeology with HERMES (GALAH) survey and Gaia provides a high-dimensional chemodynamical space of unprecedented size. We present a first analysis of a subset of this overlap, of 7066 dwarf, turn-off, and sub-giant stars. These stars have spectra from the GALAH survey and high parallax precision from the Gaia DR1 Tycho- Gaia Astrometric Solution. We investigate correlations between chemical compositions, ages, and kinematics for this s le. Stellar parameters and elemental abundances are derived from the GALAH spectra with the spectral synthesis code S PECTROSCOPY M ADE E ASY . We determine kinematics and dynamics, including action angles, from the Gaia astrometry and GALAH radial velocities. Stellar masses and ages are determined with Bayesian isochrone matching, using our derived stellar parameters and absolute magnitudes. We report measurements of Li, C, O, Na, Mg, Al, Si, K, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Y, as well as Ba and we note that we have employed non-LTE calculations for Li, O, Al, and Fe. We show that the use of astrometric and photometric data improves the accuracy of the derived spectroscopic parameters, especially log g . Focusing our investigation on the correlations between stellar age, iron abundance [Fe/H], and mean alpha-enhancement [ α /Fe] of the magnitude-selected s le, we recover the result that stars of the high- α sequence are typically older than stars in the low- α sequence, the latter spanning iron abundances of −0.7 [Fe/H] +0.5. While these two sequences become indistinguishable in [ α /Fe] vs. [Fe/H] at the metal-rich regime, we find that age can be used to separate stars from the extended high- α and the low- α sequence even in this regime. When dissecting the s le by stellar age, we find that the old stars ( Gyr) have lower angular momenta L z than the Sun, which implies that they are on eccentric orbits and originate from the inner disc. Contrary to some previous smaller scale studies we find a continuous evolution in the high- α -sequence up to super-solar [Fe/H] rather than a gap, which has been interpreted as a separate “high- α metal-rich” population. Stars in our s le that are younger than 10 Gyr, are mainly found on the low α -sequence and show a gradient in L z from low [Fe/H] ( L z L z , ⊙ ) towards higher [Fe/H] ( L z L z , ⊙ ), which implies that the stars at the ends of this sequence are likely not originating from the close solar vicinity.
Publisher: American Astronomical Society
Date: 15-05-2013
Publisher: American Astronomical Society
Date: 09-05-2017
Publisher: Zenodo
Date: 2019
Publisher: Oxford University Press (OUP)
Date: 31-03-2022
Abstract: APOGEE and GALAH are two high resolution multi-object spectroscopic surveys that provide fundamental stellar parameters and multiple elemental abundance estimates for about half a million stars in the Milky Way. Both surveys observe in different wavelength regimes and use different data reduction pipelines leading to significant offsets and trends in stellar parameters and abundances for the common stars observed in both surveys. Such systematic differences/offsets in stellar parameters and abundances make it difficult to effectively utilize them to investigate Galactic abundance trends in spite of the unique advantage provided by their complementary sky coverage and different Milky Way components they observe. Hence, we use the Cannon data-driven method selecting a training set of 4418 common stars observed by both surveys. This enables the construction of two catalogues, one with the APOGEE-scaled and the other with the GALAH-scaled stellar parameters. Using repeat observations in APOGEE and GALAH, we find high precision in metallicity (∼0.02–0.4 dex) and alpha abundances (∼0.02–0.03 dex) for spectra with good signal-to-noise ratio (SNR & 80 for APOGEE and SNR & 40 for GALAH). We use open and globular clusters to validate our parameter estimates and find small scatter in metallicity (0.06 dex) and alpha abundances (0.03 dex) in APOGEE-scaled case. The final catalogues have been cross-matched with the Gaia EDR3 catalogue to enable their use to carry out detailed chemo-dynamic studies of the Milky Way from perspectives of APOGEE and GALAH.
Publisher: Oxford University Press (OUP)
Date: 04-11-2019
Abstract: Analyses of data from spectroscopic and astrometric surveys have led to conflicting results concerning the vertical characteristics of the Milky Way. Ages are often used to provide clarity, but typical uncertainties of & per cent from photometry restrict the validity of the inferences made. Using the Kepler APOKASC s le for context, we explore the global population trends of two K2 c aign fields (3 and 6), which extend further vertically out of the Galactic plane than APOKASC. We analyse the properties of red giant stars utilizing three asteroseismic data analysis methods to cross-check and validate detections. The Bayesian inference tool PARAM is used to determine the stellar masses, radii, and ages. Evidence of a pronounced red giant branch bump and an [α/Fe] dependence on the position of the red clump is observed from the K2 fields radius distribution. Two peaks in the age distribution centred at ∼5 and ∼12 Gyr are found using a s le with σage & 35 per cent. In comparison with Kepler, we find the older peak to be more prominent for K2. This age bimodality is also observed based on a chemical selection of low-[α/Fe] (≤0.1) and high-[α/Fe] (& .1) stars. As a function of vertical distance from the Galactic mid-plane (|Z|), the age distribution shows a transition from a young to old stellar population with increasing |Z| for the K2 fields. Further coverage of c aign targets with high-resolution spectroscopy is required to increase the yield of precise ages achievable with asteroseismology.
Publisher: Zenodo
Date: 2019
Publisher: American Astronomical Society
Date: 05-2021
Abstract: We combine asteroseismology, optical high-resolution spectroscopy, and kinematic analysis for 26 halo red giant branch stars in the Kepler field in the range of −2.5 [Fe/H] −0.6. After applying theoretically motivated corrections to the seismic scaling relations, we obtain an average mass of 0.97 ± 0.03 M ⊙ for our s le of halo stars. Although this maps into an age of ∼7 Gyr, significantly younger than independent age estimates of the Milky Way stellar halo, we considered this apparently young age to be due to the overestimation of stellar mass in the scaling relations. There is no significant mass dispersion among lower red giant branch stars (log g 2), which constrains the relative age dispersion to %, corresponding to Gyr. The precise chemical abundances allow us to separate the stars with [Fe/H] −1.7 into two [Mg/Fe] groups. While the [ α /Fe] and [Eu/Mg] ratios are different between the two subs les, [ s /Eu], where s stands for Ba, La, Ce, and Nd, does not show a significant difference. These abundance ratios suggest that the chemical evolution of the low-Mg population is contributed by Type Ia supernovae, but not by low- to intermediate-mass asymptotic giant branch stars, providing a constraint on its star formation timescale as 100 Myr τ 300 Myr. We also do not detect any significant mass difference between the two [Mg/Fe] groups, thus suggesting that their formation epochs are not separated by more than 1.5 Gyr.
Publisher: Cambridge University Press (CUP)
Date: 08-2020
Publisher: American Astronomical Society
Date: 09-08-2012
Publisher: American Astronomical Society
Date: 23-11-2016
Publisher: Oxford University Press (OUP)
Date: 20-11-2013
Publisher: American Astronomical Society
Date: 20-11-2012
Publisher: Oxford University Press (OUP)
Date: 18-01-2018
DOI: 10.1093/MNRAS/STY149
Publisher: IOP Publishing
Date: 08-11-2016
Publisher: American Astronomical Society
Date: 21-11-2017
Publisher: Oxford University Press (OUP)
Date: 25-10-2019
Publisher: Oxford University Press (OUP)
Date: 21-11-2006
Publisher: Oxford University Press (OUP)
Date: 26-04-2021
Abstract: We present the results of a medium-resolution optical spectroscopic survey of 92 cool ($3000 \\,\\mathrm{ K}\\lesssim T_{\\rm eff} \\lesssim 4500\\,$K) southern TESS candidate planet hosts, and describe our spectral fitting methodology used to recover stellar parameters. We quantify model deficiencies at predicting optical fluxes, and while our technique works well for Teff, further improvements are needed for [Fe/H]. To this end, we developed an updated photometric [Fe/H] calibration for isolated main-sequence stars built upon a calibration s le of 69 cool dwarfs in binary systems, precise to $\\pm 0.19\\,$dex, from supersolar to metal poor, over 1.51 & Gaia (BP − RP) & 3.3. Our fitted Teff and R⋆ have median precisions of 0.8 per cent and 1.7 per cent, respectively, and are consistent with our s le of standard stars. We use these to model the transit light curves and determine exoplanet radii for 100 candidate planets to 3.5 per cent precision and see evidence that the planet radius gap is also present for cool dwarfs. Our results are consistent with the s le of confirmed TESS planets, with this survey representing one of the largest uniform analyses of cool TESS candidate planet hosts to date.
Publisher: EDP Sciences
Date: 31-03-2014
Publisher: American Astronomical Society
Date: 10-06-2020
Publisher: American Astronomical Society
Date: 30-01-2017
Publisher: American Astronomical Society
Date: 30-01-2017
Publisher: American Astronomical Society
Date: 17-08-2018
Publisher: Cambridge University Press (CUP)
Date: 11-2017
DOI: 10.1017/S1743921317002538
Abstract: Nearby galaxies are ideal objects for the study of the mechanisms of galaxy formation and evolution, and massive stars in nearby galaxies are useful sources to investigate the structures and formation of the galaxies. It is important to gather the contents of massive stars for a number of galaxies spanning various metallicities. We focus on the red supergiants (RSGs) in nearby galaxies NGC 4449, NGC 5055, and NGC 5457, and the photometric properties of RSGs of three galaxies were investigated using near-infrared ( JHK ) imaging data obtained from WFCAM UKIRT. The ( J − K , K ) 0 CMDs are investigated and compared with theoretical isochrones (Figure 1). The majority of RSGs in three galaxies have common age ranges from log( t yr ) = 6.9 to log( t yr ) = 7.3, and this indicates that these galaxies have experienced recent star formation within 20 Myr. Spatial correlation of RSGs with H II regions and their colour distribution were also investigated. For NGC 4449 and NGC 5457, the RSGs are spatially correlated with the H II regions, which however is not the case for NGC 5055. We found a similar colour distribution and a constant peak magnitude of M K = −11.9 for the RSGs in the three galaxies.
Publisher: American Astronomical Society
Date: 2022
Publisher: American Astronomical Society
Date: 04-11-2021
Abstract: Our picture of the age–metallicity relation for Milky Way globular clusters (MWGCs) is still highly incomplete, and the majority of MWGCs lack self-consistent age measurements. Here, we exploit deep, homogenous multiepoch Hubble Space Telescope imaging of nine MWGCs located toward the inner Milky Way to measure their relative ages, in most cases for the first time. Our relative age measurements are designed to be directly comparable to the large set of MWGC ages presented by VandenBerg et al. (V13), using identical filters, evolutionary models, and bolometric corrections, extended to the higher extinction values relevant to our target clusters. Adopting the V13 MWGC age scale, our relative age measurements imply that our target clusters are consistently very old, with a mean age of 12.9 ± 0.4 Gyr, with the exception of the young metal-rich MWGC NGC 6342. We perform two tests to validate the precision of our methodology, and discuss the implications of our target cluster loci in the MWGC age–metallicity plane. In addition, we use our fully self-consistent bolometric corrections to assess the systematic impact of variations in the total-to-selective extinction ratio R V on relative age measurements.
Publisher: Elsevier BV
Date: 10-2017
Publisher: EDP Sciences
Date: 08-2019
DOI: 10.1051/0004-6361/201935304
Abstract: The importance of studying the Gaia DR2 parallax zero-point by external means was underlined by the articles that accompanied the release, and initiated by several works making use of Cepheids, eclipsing binaries, and asteroseismology. Despite a very efficient elimination of basic-angle variations, a small fluctuation remains and shows up as a small offset in the Gaia DR2 parallaxes. By combining astrometric, asteroseismic, spectroscopic, and photometric constraints, we undertake a new analysis of the Gaia parallax offset for nearly 3000 red-giant branch (RGB) and 2200 red clump (RC) stars observed by Kepler , as well as about 500 and 700 red giants (all either in the RGB or RC phase) selected by the K2 Galactic Archaeology Program in c aigns 3 and 6. Engaging in a thorough comparison of the astrometric and asteroseismic parallaxes, we are able to highlight the influence of the asteroseismic method, and measure parallax offsets in the Kepler field that are compatible with independent estimates from literature and open clusters. Moreover, adding the K2 fields to our investigation allows us to retrieve a clear illustration of the positional dependence of the zero-point, in general agreement with the information provided by quasars. Lastly, we initiate a two-step methodology to make progress in the simultaneous calibration of the asteroseismic scaling relations and of the Gaia DR2 parallax offset, which will greatly benefit from the gain in precision with the third data release of Gaia .
Publisher: American Astronomical Society
Date: 09-05-2014
Publisher: Oxford University Press (OUP)
Date: 15-03-2016
DOI: 10.1093/MNRAS/STW611
Publisher: American Astronomical Society
Date: 06-03-2020
Publisher: Cambridge University Press (CUP)
Date: 04-2018
DOI: 10.1017/S1743921317005865
Abstract: Asteroseismology allows us to determine stellar parameters (distances, masses and ages) independently from Gaia astrometry, and it provides us with a new and complementary tool for studying stellar populations in the Galaxy. The prospects and synergies that asteroseismic and astrometric space-borne missions reserve to the field of Galactic archaeology are marvellous, and results have already started to emerge. For ex le, the study of metallicity gradients as function of age will provide powerful constraints to understand the evolution of the Milky Way disc at high-redshift.
Publisher: Oxford University Press (OUP)
Date: 16-09-2016
Publisher: Oxford University Press (OUP)
Date: 02-07-2020
Abstract: We characterize the Gaia–Enceladus–Sausage kinematic structure recently discovered in the Galactic halo using photometric metallicities from the SkyMapper survey, and kinematics from Gaia radial velocities measurements. By examining the metallicity distribution functions (MDFs) of stars binned in kinematic/action spaces, we find that the $\\sqrt{J_R}$ versus Lz space allows for the cleanest selection of Gaia–Enceladus–Sausage stars with minimal contamination from disc or halo stars formed in situ or in other past mergers. Stars with $30 \\le \\sqrt{J_R} \\le 50$ (kpc km s−1)1/2 and −500 ≤ Lz ≤ 500 kpc km s−1 have a narrow MDF centred at [Fe/H] = −1.17 dex with a dispersion of 0.34 dex. This [Fe/H] estimate is more metal-rich than literature estimates by 0.1−0.3 dex. Based on the MDFs, we find that selection of Gaia–Enceladus–Sausage stars in other kinematic/action spaces without additional population information leads to contaminated s les. The clean Gaia–Enceladus–Sausage s le selected according to our criteria is slightly retrograde and lies along the blue sequence of the high VT halo colour magnitude diagram dual sequence. Using a galaxy mass–metallicity relation derived from cosmological simulations and assuming a mean stellar age of 10 Gyr, we estimate the mass of the Gaia–Enceladus–Sausage progenitor satellite to be 108.85–9.85 M⊙, which is consistent with literature estimates based on disc dynamic and simulations. Additional information on detailed abundances and ages would be needed for a more sophisticated selection of purely Gaia–Enceladus–Sausage stars.
Publisher: Oxford University Press (OUP)
Date: 16-05-2018
Publisher: EDP Sciences
Date: 03-2010
Publisher: Oxford University Press (OUP)
Date: 30-01-2019
DOI: 10.1093/MNRAS/STZ296
Publisher: Cambridge University Press (CUP)
Date: 08-2015
DOI: 10.1017/S1743921316006347
Abstract: Asteroseismology has the capability of precisely determining stellar properties that would otherwise be inaccessible, such as radii, masses, and thus ages of field stars. When coupling this information with classical determinations of stellar parameters, such as metallicities, effective temperatures, and angular diameters, powerful new diagnostics for Galactic studies can be obtained. An overview of the ongoing Strömgren survey for Asteroseismology and Galactic Archaeology (SAGA) is presented, along with recent results using asteroseismology to investigate the vertical age structure of the Milky Way disc.
Publisher: EDP Sciences
Date: 2013
Publisher: EDP Sciences
Date: 11-2010
Publisher: American Astronomical Society
Date: 27-07-2020
Publisher: EDP Sciences
Date: 03-2018
DOI: 10.1051/0004-6361/201732147
Abstract: Context. The surface structures and dynamics of cool stars are characterised by the presence of convective motions and turbulent flows which shape the emergent spectrum. Aims. We used realistic three-dimensional (3D) radiative hydrodynamical simulations from the S TAGGER -grid to calculate synthetic spectra with the radiative transfer code OPTIM3D for stars with different stellar parameters to predict photometric colours and convective velocity shifts. Methods. We calculated spectra from 1000 to 200 000 Å with a constant resolving power of λ ∕ Δλ = 20 000 and from 8470 and 8710 Å ( Gaia Radial Velocity Spectrometer – RVS – spectral range) with a constant resolving power of λ ∕ Δλ = 300 000. Results. We used synthetic spectra to compute theoretical colours in the Johnson-Cousins UBV ( RI ) C , SDSS, 2MASS, Gaia , SkyMapper, Strömgren systems, and HST-WFC3. Our synthetic magnitudes are compared with those obtained using 1D hydrostatic models. We showed that 1D versus 3D differences are limited to a small percent except for the narrow filters that span the optical and UV region of the spectrum. In addition, we derived the effect of the convective velocity fields on selected Fe I lines. We found the overall convective shift for 3D simulations with respect to the reference 1D hydrostatic models, revealing line shifts of between −0.235 and +0.361 km s −1 . We showed a net correlation of the convective shifts with the effective temperature: lower effective temperatures denote redshifts and higher effective temperatures denote blueshifts. We conclude that the extraction of accurate radial velocities from RVS spectra need an appropriate wavelength correction from convection shifts. Conclusions. The use of realistic 3D hydrodynamical stellar atmosphere simulations has a small but significant impact on the predicted photometry compared with classical 1D hydrostatic models for late-type stars. We make all the spectra publicly available for the community through the POLLUX database.
Publisher: EDP Sciences
Date: 06-2010
Publisher: American Astronomical Society
Date: 27-07-2020
Publisher: Cambridge University Press (CUP)
Date: 11-2009
DOI: 10.1017/S174392131000414X
Abstract: We present Li abundances for 73 stars in the metallicity range −3.5 [Fe/H] −1.0 using improved IRFM temperatures (Casagrande et al . 2010) with precise E ( B-V ) values obtained mostly from interstellar NaI D lines, and high-quality equivalent widths (σ EW ~ 3%). At all metallicities we uncover a fine-structure in the Li abundances of Spite plateau stars, which we trace to Li depletion that depends on both metallicity and mass. Models including atomic diffusion and turbulent mixing seem to reproduce the observed Li depletion assuming a primordial Li abundance A Li = 2.64 dex (MARCS models) or 2.72 (Kurucz overshooting models), in good agreement with current predictions ( A Li = 2.72) from standard BBN. We are currently expanding our s le to have a better coverage of different evolutionary stages at the high and low metallicity ends, in order to verify our findings.
Publisher: Wiley
Date: 02-2013
Abstract: Asteroseismology has been extremely successful in determining the properties of stars in different evolutionary stages with a remarkable level of precision. However, to fully exploit its potential, robust methods for estimating stellar parameters are required and independent verification of the results is needed. In this talk, I present a new technique developed to obtain stellar properties by coupling asteroseismic analysis with the infrared flux method. Using two global seismic observables and multi‐band photometry, the technique determines masses, radii, effective temperatures, bolometric fluxes, and thus distances for field stars in a self‐consistent manner. Applying our method to a s le of solar‐like oscillators in the Kepler field that have accurate Hipparcos parallaxes, we find agreement in our distance determinations to better than 5 %. Comparison with measurements of spectroscopic effective temperatures and interferometric radii also validate our results, and show that our technique can be applied to stars evolved beyond the main‐sequence phase. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Publisher: Oxford University Press (OUP)
Date: 11-06-2018
Publisher: American Astronomical Society
Date: 06-09-2012
Publisher: American Astronomical Society
Date: 18-12-2015
Publisher: American Astronomical Society
Date: 06-08-2019
Publisher: Springer Science and Business Media LLC
Date: 12-10-2018
DOI: 10.1038/S41467-018-06525-2
Abstract: Understanding the drivers of yield levels under climate change is required to support adaptation planning and respond to changing production risks. This study uses an ensemble of crop models applied on a spatial grid to quantify the contributions of various climatic drivers to past yield variability in grain maize and winter wheat of European cropping systems (1984–2009) and drivers of climate change impacts to 2050. Results reveal that for the current genotypes and mix of irrigated and rainfed production, climate change would lead to yield losses for grain maize and gains for winter wheat. Across Europe, on average heat stress does not increase for either crop in rainfed systems, while drought stress intensifies for maize only. In low-yielding years, drought stress persists as the main driver of losses for both crops, with elevated CO 2 offering no yield benefit in these years.
Publisher: Cambridge University Press (CUP)
Date: 07-2017
DOI: 10.1017/S1743921317007499
Abstract: We investigate the vertical metallicity gradients of five mono-age stellar populations between 0 and 11 Gyr for a s le of 18 435 dwarf stars selected from the cross-matched Tycho-Gaia Astrometric Solution (TGAS) and RAdial Velocity Experiment (RAVE) Data Release 5. We find a correlation between the vertical metallicity gradients and age, with no vertical metallicity gradient in the youngest population and an increasingly steeper negative vertical metallicity gradient for the older stellar populations. We also find that the intrinsic dispersion in metallicity increases steadily with age. Our results are consistent with a scenario that thin disk stars formed from a flaring thin star-forming disk.
Publisher: EDP Sciences
Date: 30-06-2023
DOI: 10.1051/0004-6361/202346149
Abstract: Context. Cool stars, such as M giants, can only be analyzed in the near-infrared (NIR) regime due to the ubiquitous titanium oxide features in optical spectra of stars with T eff 4000 K. In dust-obscured regions, the inner bulge and Galactic center region, the intrinsically bright M giants observed in the NIR are an optimal option for studying stellar abundances and the chemical evolution of stellar populations. Because of the uncertainties in photometric methods, a method for determining the stellar parameters for M giants from the NIR spectra themselves is needed. Aims. We develop a method for determining the stellar parameters for M giants from the NIR spectra. We validate the method by deriving the stellar parameters for nearby well-studied M giants with spectra from the spectral library of the Immersion GRating INfrared Spectrograph (IGRINS). We demonstrate the accuracy and precision of our method by determining the stellar parameters and α -element trends versus metallicity for solar neighborhood M giants. Methods. We carried out new observations of 44 M giant stars with IGRINS mounted on the Gemini South telescope. We also obtained the full H and K band IGRINS spectra of six nearby well-studied M giants at a spectral resolving power of R = 45 000 from the IGRINS spectral library. We used the tool called spectroscopy made easy in combination with one-dimensional (1D) model atmospheres in a radiative and convective scheme (MARCS) stellar atmosphere models to model the synthetic spectrum that fits the observed spectrum best. Results. The effective temperatures that we derive from our new method (tested for 3400 ≲ T eff ≲ 4000 K here) agree excellently with those of the six nearby well-studied M giants, which indicates that the accuracy is indeed high. For the 43 solar neighborhood M giants, our T eff , log g , [Fe/H], ξ micro , [C/Fe], [N/Fe], and [O/Fe] agree with APOGEE with mean differences and a scatter (our method – APOGEE) of −67±33 K, −0.31±0.15 dex, 0.02±0.05 dex, 0.22±0.13 km s −1 , −0.05±0.06 dex, 0.06±0.06 dex, and 0.02±0.09 dex, respectively. Furthermore, the tight offset with a small dispersion compared to the APOGEE T eff indicates a high precision in our derived temperatures and those derived from the APOGEE pipeline. The typical uncertainties in the stellar parameters are found to be ±100 K in T eff , ±0.2 dex in log g , ±0.1 dex in [Fe/H], and ±0.1 km s −1 in ξ micro . The α -element trends versus metallicity for Mg, Si, Ca, and Ti are consistent with the APOGEE DR17 trends for the same stars and with the GILD optical trends. We also find a clear enhancement in the abundances for thick-disk stars.
Publisher: Oxford University Press (OUP)
Date: 27-02-2018
DOI: 10.1093/MNRAS/STY525
Publisher: Oxford University Press (OUP)
Date: 08-2014
Publisher: EDP Sciences
Date: 02-2022
DOI: 10.1051/0004-6361/202140863
Abstract: We introduce the SAPP (Stellar Abundances and atmospheric Parameters Pipeline), the prototype of the code that will be used to determine parameters of stars observed within the core program of the PLATO space mission. The pipeline is based on the Bayesian inference and provides effective temperature, surface gravity, metallicity, chemical abundances, and luminosity. The code in its more general version has a much wider range of potential applications. It can also provide masses, ages, and radii of stars and can be used with stellar types not targeted by the PLATO core program, such as red giants. We validate the code on a set of 27 benchmark stars that includes 19 FGK-type dwarfs, 6 GK-type subgiants, and 2 red giants. Our results suggest that combining various observables is the optimal approach, as this allows the degeneracies between different parameters to be broken and yields more accurate values of stellar parameters and more realistic uncertainties. For the PLATO core s le, we obtain a typical uncertainty of 27 (syst.) ± 37 (stat.) K for T eff , 0.00 ± 0.01 dex for log g , 0.02 ± 0.02 dex for metallicity [Fe/H], −0.01 ± 0.03 R ⊙ for radii, −0.01 ± 0.05 M ⊙ for stellar masses, and −0.14 ± 0.63 Gyr for ages. We also show that the best results are obtained by combining the ν max scaling relation with stellar spectra. This resolves the notorious problem of degeneracies, which is particularly important for F-type stars.
Publisher: Oxford University Press (OUP)
Date: 05-11-2014
Publisher: Oxford University Press (OUP)
Date: 29-04-2016
Publisher: European Southern Observatory (ESO)
Date: 2019
Publisher: American Astronomical Society
Date: 19-01-2017
Publisher: European Southern Observatory (ESO)
Date: 2019
Publisher: American Astronomical Society
Date: 04-08-2015
Publisher: Oxford University Press (OUP)
Date: 12-01-2018
Publisher: American Astronomical Society
Date: 09-04-2014
Publisher: EDP Sciences
Date: 09-2017
Publisher: Valley International
Date: 17-07-2021
DOI: 10.18535/IJSRM/V9I07.EL02
Abstract: Understanding the current state of the Internationalisation of postgraduate courses in Brazil was essential to serve as a basis for constructing effective policies in funding agencies. It also helps to understand the capacity of the higher education institution to carry out more effective strategic planning and internationalisation plans. This study looks at replies to a Brazilian national funding agency (CAPES) questionnaire on Internationalisation within Higher Education Institutes in Brazil, based on the postgraduate experience. Results showed that Internationalisation is based on mobility with little comprehensive thinking on its role towards academic achievement within the Postgraduate Programs realities, beyond the mobile in idual. English language skills need to be improved. While most institutions have offices that treat this theme, they lack an active engagement with the postgraduate programs and strategic planning, seen as vital for almost all institutions. Resources are necessary to build infrastructure and capacitate lecturers and staff to this end.
Publisher: Springer International Publishing
Date: 16-11-2015
Publisher: American Astronomical Society
Date: 08-09-2010
Publisher: American Astronomical Society
Date: 23-06-2017
Publisher: Springer Science and Business Media LLC
Date: 10-11-2009
Publisher: American Astronomical Society
Date: 23-06-2017
Publisher: Oxford University Press (OUP)
Date: 23-03-2016
DOI: 10.1093/MNRAS/STW676
Publisher: American Astronomical Society
Date: 26-10-2010
Publisher: Oxford University Press (OUP)
Date: 24-08-2018
Publisher: Oxford University Press (OUP)
Date: 09-02-2017
DOI: 10.1093/MNRAS/STX013
Publisher: American Astronomical Society
Date: 29-01-2021
Publisher: American Astronomical Society
Date: 24-01-2018
Publisher: EDP Sciences
Date: 2014
Publisher: American Astronomical Society
Date: 15-09-2011
Publisher: EDP Sciences
Date: 2021
DOI: 10.1051/0004-6361/202038307
Abstract: Ensemble studies of red-giant stars with exquisite asteroseismic ( Kepler ), spectroscopic (APOGEE), and astrometric ( Gaia ) constraints offer a novel opportunity to recast and address long-standing questions concerning the evolution of stars and of the Galaxy. Here, we infer masses and ages for nearly 5400 giants with available Kepler light curves and APOGEE spectra using the code PARAM , and discuss some of the systematics that may affect the accuracy of the inferred stellar properties. We then present patterns in mass, evolutionary state, age, chemical abundance, and orbital parameters that we deem robust against the systematic uncertainties explored. First, we look at age-chemical-abundances ([Fe/H] and [ α /Fe]) relations. We find a dearth of young, metal-rich ([Fe/H] 0.2) stars, and the existence of a significant population of old (8−9 Gyr), low-[ α /Fe], super-solar metallicity stars, reminiscent of the age and metallicity of the well-studied open cluster NGC 6791. The age-chemo-kinematic properties of these stars indicate that efficient radial migration happens in the thin disc. We find that ages and masses of the nearly 400 α -element-rich red-giant-branch (RGB) stars in our s le are compatible with those of an old (∼11 Gyr), nearly coeval, chemical-thick disc population. Using a statistical model, we show that the width of the observed age distribution is dominated by the random uncertainties on age, and that the spread of the inferred intrinsic age distribution is such that 95% of the population was born within ∼1.5 Gyr. Moreover, we find a difference in the vertical velocity dispersion between low- and high-[α/Fe] populations. This discontinuity, together with the chemical one in the [α/Fe] versus [Fe/H] diagram, and with the inferred age distributions, not only confirms the different chemo-dynamical histories of the chemical-thick and thin discs, but it is also suggestive of a halt in the star formation (quenching) after the formation of the chemical-thick disc. We then exploit the almost coeval α -rich population to gain insight into processes that may have altered the mass of a star along its evolution, which are key to improving the mapping of the current, observed, stellar mass to the initial mass and thus to the age. Comparing the mass distribution of stars on the lower RGB ( R 11 R ⊙ ) with those in the red clump (RC), we find evidence for a mean integrated RGB mass loss ⟨Δ M ⟩ = 0.10 ± 0.02 M ⊙ . Finally, we find that the occurrence of massive ( M ≳ 1.1 M ⊙ ) α -rich stars is of the order of 5% on the RGB, and significantly higher in the RC, supporting the scenario in which most of these stars had undergone an interaction with a companion.
Publisher: European Southern Observatory (ESO)
Date: 2019
Publisher: Oxford University Press (OUP)
Date: 15-01-2013
DOI: 10.1093/MNRAS/STS648
Publisher: Oxford University Press (OUP)
Date: 10-08-2021
Abstract: In order to accurately determine stellar properties, knowledge of the effective temperature of stars is vital. We implement Gaia and 2MASS photometry in the InfraRed Flux Method and apply it to over 360 000 stars across different evolutionary stages in the GALAH DR3 survey. We derive colour-effective temperature relations that take into account the effect of metallicity and surface gravity over the range $4000\\, \\rm {K}\\lesssim T_{\\rm {eff}}\\lesssim 8000\\, \\rm {K}$, from very metal-poor stars to supersolar metallicities. The internal uncertainty of these calibrations is of order 40–80 K depending on the colour combination used. Comparison against solar-twins, Gaia benchmark stars, and the latest interferometric measurements validates the precision and accuracy of these calibrations from F to early M spectral types. We assess the impact of various sources of uncertainties, including the assumed extinction law, and provide guidelines to use our relations. Robust solar colours are also derived.
Publisher: Oxford University Press (OUP)
Date: 06-02-2021
Abstract: We establish a quantitative relationship between photometric and spectroscopic detections of solar-like oscillations using ab initio, 3D, hydrodynamical numerical simulations of stellar atmospheres. We present a theoretical derivation as a proof of concept for our method. We perform realistic spectral line formation calculations to quantify the ratio between luminosity and radial velocity litude for two case studies: the Sun and the red giant ϵ Tau. Luminosity litudes are computed based on the bolometric flux predicted by 3D simulations with granulation background modelled the same way as asteroseismic observations. Radial velocity litudes are determined from the wavelength shift of synthesized spectral lines with methods closely resembling those used in Birmingham Solar Oscillations Network (BiSON) and Stellar Oscillations Network Group (SONG) observations. Consequently, the theoretical luminosity to radial velocity litude ratios are directly comparable with corresponding observations. For the Sun, we predict theoretical ratios of 21.0 and 23.7 ppm [m s−1]−1 from BiSON and SONG, respectively, in good agreement with observations 19.1 and 21.6 ppm [m s−1]−1. For ϵ Tau, we predict K2 and SONG ratios of 48.4 ppm [m s−1]−1, again in good agreement with observations 42.2 ppm [m s−1]−1, and much improved over the result from conventional empirical scaling relations that give 23.2 ppm [m s−1]−1. This study thus opens the path towards a quantitative understanding of solar-like oscillations, via detailed modelling of 3D stellar atmospheres.
Publisher: EDP Sciences
Date: 26-05-2011
Publisher: Oxford University Press (OUP)
Date: 24-07-2015
Publisher: Oxford University Press (OUP)
Date: 30-06-2011
Publisher: IOP Publishing
Date: 12-2008
Publisher: American Astronomical Society
Date: 06-2021
Abstract: We present a new identity card for the cluster NGC 6440 in the Galactic Bulge. We have used a combination of high-resolution Hubble Space Telescope images, wide-field ground-based observations performed with the ESO-FORS2, and the public survey catalog Pan-STARRS to determine the gravitational center, projected density profile, and structural parameters of this globular from resolved star counts. The new determination of the cluster center differs by ∼2″ (corresponding to 0.08 pc) from the previous estimate, which was based on the surface brightness peak. The star density profile, extending out to 700″ from the center and suitably decontaminated from the Galactic field contribution, is best fit by a King model with a significantly higher concentration ( c = 1.86 ± 0.06) and smaller core radius ( r c = 6.″4 ± 0.″3) with respect to the literature values. By taking advantage of high-quality optical and near-IR color–magnitude diagrams, we also estimated the cluster age, distance, and reddening. The luminosity of the red giant branch bump was also determined. This study indicates that the extinction coefficient in the bulge in the direction of the cluster has a value ( R V = 2.7) that is significantly lower than that traditionally used for the Galaxy ( R V = 3.1). The corresponding best-fit values of the age, distance, and color excess of NGC 6440 are 13 Gyr, 8.3 kpc, and E ( B − V ) ∼ 1.27. These new determinations also allowed us to update the values of the central ( t rc = 2.5 10 7 yr) and half-mass ( t rh = 10 9 yr) relaxation times, suggesting that NGC 6440 is in a dynamically evolved stage.
Publisher: Oxford University Press (OUP)
Date: 08-07-2019
Abstract: Chemistry and kinematic studies can determine the origins of stellar population across the Milky Way. The metallicity distribution function of the bulge indicates that it comprises multiple populations, the more metal-poor end of which is particularly poorly understood. It is currently unknown if metal-poor bulge stars ([Fe/H] −1 dex) are part of the stellar halo in the inner most region, or a distinct bulge population or a combination of these. Cosmological simulations also indicate that the metal-poor bulge stars may be the oldest stars in the Galaxy. In this study, we successfully target metal-poor bulge stars selected using SkyMapper photometry. We determine the stellar parameters of 26 stars and their elemental abundances for 22 elements using R∼ 47 000 VLT/UVES spectra and contrast their elemental properties with that of other Galactic stellar populations. We find that the elemental abundances we derive for our metal-poor bulge stars have lower overall scatter than typically found in the halo. This indicates that these stars may be a distinct population confined to the bulge. If these stars are, alternatively, part of the innermost distribution of the halo, this indicates that the halo is more chemically homogeneous at small Galactic radii than at large radii. We also find two stars whose chemistry is consistent with second-generation globular cluster stars. This paper is the first part of the Chemical Origins of Metal-poor Bulge Stars (COMBS) survey that will chemodynamically characterize the metal-poor bulge population.
Publisher: Oxford University Press (OUP)
Date: 08-05-2023
Abstract: In this study we combine asteroseismic, spectroscopic, and kinematic information to perform a detailed analysis of a s le of 16 stars from the Kepler field. Our selection focuses on stars that appear to contradict Galactic chemical evolution models: young and α-rich, old and metal-rich, as well as other targets with unclear classification in past surveys. Kinematics are derived from Gaia DR3 parallaxes and proper motions, and high-resolution spectra from HIRES/Keck are used to calculate chemical abundances for over 20 elements. This information is used to perform careful checks on asteroseismic masses and ages derived via grid-based modelling. Among the seven stars previously classified as young and α-rich, only one seems to be an unambiguously older object masking its true age. We confirm the existence of two very old (≥11 Gyr), super metal-rich (≥0.1 dex) giants. These two stars have regular thin disc chemistry and in-plane solar circle orbits that fit well in the picture of radial migration via the churning mechanism. The alternative explanation that these stars have younger ages would require mass-loss rates that strongly increase with increasing metallicity. Finally, we suggest further investigations to explore the suitability of Zn as a chemical clock in red giants.
Publisher: EDP Sciences
Date: 12-2022
DOI: 10.1051/0004-6361/202244571
Abstract: Blue large- litude pulsators (BLAPs) are a newly discovered type of variable star. Their typical pulsation periods are on the order of a few tens of minutes, with relatively large litudes of 0.2–0.4 mag in optical bands, and their rates of period changes are on the order of 10 −7 yr −1 (both positive and negative). They are extremely rare objects and attempts to explain their origins and internal structures have attracted a great deal of attention. Previous studies have proposed that BLAPs may be pre-white dwarfs, with masses around 0.3 M ⊙ , or core-helium-burning stars in the range of ∼0.7 − 1.1 M ⊙ . In this work, we use a number of MESA models to compute and explore whether BLAPs could be explained as shell helium-burning subdwarfs type B (SHeB sdBs). The models that best match existing observational constraints have helium core masses in the range of ∼0.45 − 0.5 M ⊙ . Our model predicts that the positive rate of period change may evolve to negative. The formation channels for SHeB sdBs involve binary evolution and although the vast majority of BLAPs do not appear to be binaries (with the exception of HD 133729), the observational constraints are still very poor. Motivated by these findings, we explored the Roche lobe overflow channel. Of the 304 binary evolution models we computed, about half of them are able to produce SHeB sdBs in long-period binaries that evade detection from the limited observations that are currently available.
Publisher: American Astronomical Society
Date: 10-02-2023
Abstract: We propose Sirius as an improved zero-point-defining star and calibrate its spectrum to an accuracy of ∼0.6% in both the visible and infrared. This result is based on a newly derived independent calibration in the visible of similar accuracy to the previous standard one, with which it is combined. We use a large variety of approaches in the infrared to reach about three times smaller error than for previous absolute calibrations. The results in the two wavelength regimes are in agreement, providing a consistent link from the visible throughout the near- and mid-infrared. The Sirius-based zero-point at 5557.5 Å (in vacuum) is 13.436 ± 0.081 × 10 −12 W cm −2 μ m −1 , based on the improved value for Vega of 3.473 ± 0.018 × 10 −12 W cm −2 μ m −1 and the measured magnitude difference between the two stars. At 2.1603 μ m, the zero-point is 4.225 ± 0.025 × 10 −14 W cm −2 μ m −1 taking Sirius at a magnitude of −1.395. A jackknife analysis indicates that there are no serious systematic errors in these results. We consider selection of secondary standards that can extend the calibration over the sky. Despite more than a century in this role, normal A-stars are not suitable, although Am and Ap stars may be. G-stars older than ∼1 Gyr are good candidates if accurate temperatures can be measured. White dwarfs are suitable from the visible through the near-infrared, but their properties are unexplored at the necessary level at the longer infrared wavelengths, and for most facilities they are too faint there. Finally, as a further test of the calibration, we demonstrate an upgraded infrared flux method to determine accurate stellar diameters from K -band photometry.
Publisher: Oxford University Press (OUP)
Date: 05-04-2018
DOI: 10.1093/MNRAS/STY865
Publisher: American Astronomical Society
Date: 11-12-2013
Publisher: EDP Sciences
Date: 25-11-2010
Publisher: EDP Sciences
Date: 2012
Publisher: American Astronomical Society
Date: 24-06-2016
Publisher: Oxford University Press (OUP)
Date: 18-02-2021
Abstract: Open clusters are unique tracers of the history of our own Galaxy’s disc. According to our membership analysis based on Gaia astrometry, out of the 226 potential clusters falling in the footprint of the GALactic Archaeology with HERMES (GALAH) survey or the Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey, we find that 205 have secure members that were observed by at least one of the surveys. Furthermore, members of 134 clusters have high-quality spectroscopic data that we use to determine their chemical composition. We leverage this information to study the chemical distribution throughout the Galactic disc of 21 elements, from C to Eu. The radial metallicity gradient obtained from our analysis is −0.076 ± 0.009 dex kpc−1, which is in agreement with previous works based on smaller s les. Furthermore, the gradient in the [Fe/H]–guiding radius (rguid) plane is −0.073 ± 0.008 dex kpc−1. We show consistently that open clusters trace the distribution of chemical elements throughout the Galactic disc differently than field stars. In particular, at the given radius, open clusters show an age–metallicity relation that has less scatter than field stars. As such scatter is often interpreted as an effect of radial migration, we suggest that these differences are due to the physical selection effect imposed by our Galaxy: clusters that would have migrated significantly also had higher chances to get destroyed. Finally, our results reveal trends in the [X/Fe]–rguid–age space, which are important to understand production rates of different elements as a function of space and time.
Publisher: Oxford University Press (OUP)
Date: 05-2010
Publisher: Oxford University Press (OUP)
Date: 18-01-2018
DOI: 10.1093/MNRAS/STY150
Publisher: Oxford University Press (OUP)
Date: 06-10-2016
Publisher: EDP Sciences
Date: 10-2014
Publisher: Oxford University Press (OUP)
Date: 03-11-2016
Publisher: IOP Publishing
Date: 10-2015
DOI: 10.1086/683103
Publisher: American Astronomical Society
Date: 04-2022
Abstract: The Sloan Extension for Galactic Understanding and Exploration 2 (SEGUE-2) obtained 128,288 low-resolution spectra ( R ∼ 1800) of 118,958 unique stars in the first year of the Sloan Digital Sky Survey III (2008–2009). SEGUE-2 targeted prioritized distant halo tracers (blue horizontal-branch stars, K giants, and M giants) and metal-poor or kinematically hot populations. The main goal of SEGUE-2 was to target stars in the distant halo and measure their kinematics and chemical abundances to learn about the formation and evolution of the Milky Way. We present the SEGUE-2 field placement and target selection strategies. We discuss the success rate of the targeting based on the SEGUE-2 spectra and other spectroscopic and astrometric surveys. We describe the final SEGUE-2/SDSS-III improvements to the stellar parameter determinations based on the SEGUE Stellar Parameter Pipeline. We report a ( g − i ) color−effective temperature relation calibrated to the IRFM. We evaluate the accuracy and uncertainties associated with these stellar parameters by comparing with fundamental parameters, a s le of high-resolution spectra of SEGUE stars analyzed homogeneously, stars in well-studied clusters, and stars observed in common by the APOGEE survey. The final SEGUE spectra, calibration data, and derived parameters described here were released in SDSS-III Data Release 9 and continue to be included in all subsequent SDSS Data Releases. Because of its faint limiting magnitude and emphasis on the distant halo, the public SEGUE-2 data remain an important resource for the spectroscopy of stars in the Milky Way.
Publisher: EDP Sciences
Date: 28-07-2016
Publisher: Cambridge University Press (CUP)
Date: 08-2020
DOI: 10.1017/S1743921319005118
Abstract: I use SkyMapper DR1.1 to explore the quality of its uvgriz photometry, and zero-points. I introduce a formalism to derive photometric zero-points across the sky by benchmarking against stars with well known effective temperatures, bypassing the need for absolute spectrophotometry.
Publisher: Oxford University Press (OUP)
Date: 21-12-2018
Publisher: Oxford University Press (OUP)
Date: 08-12-2021
Abstract: In this work, we combine information from solar-like oscillations, high-resolution spectroscopy, and Gaia astrometry to derive stellar ages, chemical abundances, and kinematics for a group of seven metal-poor red giants and characterize them in a multidimensional chrono-chemo-dynamical space. Chemical abundance ratios were derived through classical spectroscopic analysis employing 1D LTE atmospheres on Keck/HIRES spectra. Stellar ages, masses, and radii were calculated with grid-based modelling, taking advantage of availability of asteroseismic information from Kepler. The dynamical properties were determined with galpy using Gaia EDR3 astrometric solutions. Our results suggest that underestimated parallax errors make the effect of Gaia parallaxes more important than different choices of model grid or – in the case of stars ascending the red giant branch – mass-loss prescription. Two of the stars in this study are identified as potentially evolved halo blue stragglers. Four objects are likely members of the accreted Milky Way halo, and their possible relationship with known accretion events is discussed.
Publisher: American Astronomical Society
Date: 16-09-2013
Publisher: Oxford University Press (OUP)
Date: 06-05-2021
Abstract: The ensemble of chemical element abundance measurements for stars, along with precision distances and orbit properties, provides high-dimensional data to study the evolution of the Milky Way. With this third data release of the Galactic Archaeology with HERMES (GALAH) survey, we publish 678 423 spectra for 588 571 mostly nearby stars (81.2 per cent of stars are within & kpc), observed with the HERMES spectrograph at the Anglo-Australian Telescope. This release (hereafter GALAH+ DR3) includes all observations from GALAH Phase 1 (bright, main, and faint survey, 70 per cent), K2-HERMES (17 per cent), TESS-HERMES (5 per cent), and a subset of ancillary observations (8 per cent) including the bulge and & stellar clusters. We derive stellar parameters Teff, log g, [Fe/H], vmic, vbroad, and vrad using our modified version of the spectrum synthesis code Spectroscopy Made Easy (sme) and 1D marcs model atmospheres. We break spectroscopic degeneracies in our spectrum analysis with astrometry from Gaia DR2 and photometry from 2MASS. We report abundance ratios [X/Fe] for 30 different elements (11 of which are based on non-LTE computations) covering five nucleosynthetic pathways. We describe validations for accuracy and precision, flagging of peculiar stars/measurements and recommendations for using our results. Our catalogue comprises 65 per cent dwarfs, 34 per cent giants, and 1 per cent other/unclassified stars. Based on unflagged chemical composition and age, we find 62 per cent young low-$\\alpha$, 9 per cent young high-$\\alpha$, 27 per cent old high-$\\alpha$, and 2 per cent stars with [Fe/H] ≤ −1. Based on kinematics, 4 per cent are halo stars. Several Value-Added-Catalogues, including stellar ages and dynamics, updated after Gaia eDR3, accompany this release and allow chrono-chemodynamic analyses, as we showcase.
Publisher: EDP Sciences
Date: 08-2020
DOI: 10.1051/0004-6361/202037590
Abstract: Context. Benchmark stars are crucial as validating standards for current as well as future large stellar surveys of the Milky Way. However, the number of suitable metal-poor benchmark stars is currently limited, owing to the difficulty in determining reliable effective temperatures ( T eff ) in this regime. Aims. We aim to construct a new set of metal-poor benchmark stars based on reliable interferometric effective temperature determinations and a homogeneous analysis. The aim is to reach a precision of 1% in T eff , as is crucial for sufficiently accurate determinations of the full set of fundamental parameters and abundances for the survey sources. Methods. We observed ten late-type metal-poor dwarfs and giants: HD 2665, HD 6755, HD 6833, HD 103095, HD 122563, HD 127243, HD 140283, HD 175305, HD 221170, and HD 224930. Only three of them (HD 103095, HD 122563, and HD 140283) have previously been used as benchmark stars. For the observations, we used the high-angular-resolution optical interferometric instrument PAVO at the CHARA array. We modelled angular diameters using 3D limb-darkening models and determined effective temperatures directly from the Stefan-Boltzmann relation, with an iterative procedure to interpolate over tables of bolometric corrections. Surface gravities (log( g )) were estimated from comparisons to Dartmouth stellar evolution model tracks. We collected spectroscopic observations from the ELODIE and FIES spectrographs and estimated metallicities ([Fe/H]) from a 1D non-local thermodynamic equilibrium (NLTE) abundance analysis of unblended lines of neutral and singly ionised iron. Results. We inferred T eff to better than 1% for five of the stars (HD 103095, HD 122563, HD 127243, HD 140283, and HD 224930). The effective temperatures of the other five stars are reliable to between 2 and 3% the higher uncertainty on the T eff for those stars is mainly due to their having a larger uncertainty in the bolometric fluxes. We also determined log( g ) and [Fe/H] with median uncertainties of 0.03 dex and 0.09 dex, respectively. Conclusions. This study presents reliable and homogeneous fundamental stellar parameters for ten metal-poor stars that can be adopted as a new set of benchmarks. The parameters are based on our consistent approach of combining interferometric observations, 3D limb-darkening-modelling and spectroscopic observations. The next paper in this series will extend this approach to dwarfs and giants in the metal-rich regime.
Publisher: Oxford University Press (OUP)
Date: 15-09-2021
Abstract: Identifying stars found in the Milky Way as having formed in situ or accreted can be a complex and uncertain undertaking. We use Gaia kinematics and APOGEE elemental abundances to select stars belonging to the Gaia-Sausage-Enceladus (GSE) and Sequoia accretion events. These s les are used to characterize the GSE and Sequoia population metallicity distribution functions, elemental abundance patterns, age distributions, and progenitor masses. We find that the GSE population has a mean [Fe/H] ∼ −1.15 and a mean age of 10–12 Gyr. GSE has a single sequence in [Mg/Fe] versus [Fe/H] consistent with the onset of SN Ia Fe contributions and uniformly low [Al/Fe] of ∼−0.25 dex. The derived properties of the Sequoia population are strongly dependent on the kinematic selection. We argue the selection with the least contamination is Jϕ/Jtot & −0.6 and (Jz − JR)/Jtot & 0.1. This results in a mean [Fe/H] ∼ −1.3 and a mean age of 12–14 Gyr. The Sequoia population has a complex elemental abundance distribution with mainly high-[Mg/Fe] stars. We use the GSE [Al/Fe] versus [Mg/H] abundance distribution to inform a chemically based selection of accreted stars, which is used to remove possible contaminant stars from the GSE and Sequoia s les.
Publisher: EDP Sciences
Date: 2015
Publisher: Oxford University Press (OUP)
Date: 09-02-2018
DOI: 10.1093/MNRAS/STY319
Publisher: Cambridge University Press (CUP)
Date: 05-2013
DOI: 10.1017/S1743921313006583
Abstract: Accurate characterization of stellar populations is of prime importance to correctly understand the formation and evolution process of our Galaxy. The field of asteroseismology has been particularly successful in such an endeavor providing fundamental parameters for large s les of stars in different evolutionary phases. We present our results on determinations of masses, radii, and distances of stars in the CoRoT and Kepler fields, showing that we can map and date different regions of the galactic disk and distinguish gradients in the distribution of stellar properties at different heights. We further review how asteroseismic determinations can produce a unique set of constraints, including ages, outside the solar neighborhood for galactic chemical evolution models.
Publisher: Oxford University Press (OUP)
Date: 26-08-2016
Publisher: Springer Science and Business Media LLC
Date: 26-02-2018
DOI: 10.1038/NATURE25490
Abstract: Our Galaxy is thought to have an active evolutionary history, dominated over the past ten billion years or so by star formation, the accretion of cold gas and, in particular, the merging of clumps of baryonic and dark matter. The stellar halo-the faint, roughly spherical component of the Galaxy-reveals rich 'fossil' evidence of these interactions, in the form of stellar streams, substructures and chemically distinct stellar components. The effects of interactions with dwarf galaxies on the content and morphology of the Galactic disk are still being explored. Recent studies have identified kinematically distinct stellar substructures and moving groups of stars in our Galaxy, which may have extragalactic origins. There is also mounting evidence that stellar overdensities (regions with greater-than-average stellar density) at the interface between the outer disk and the halo could have been caused by the interaction of a dwarf galaxy with the disk. Here we report a spectroscopic analysis of 14 stars from two stellar overdensities, each lying about five kiloparsecs above or below the Galactic plane-locations suggestive of an association with the stellar halo. We find that the chemical compositions of these two groups of stars are almost identical, both within and between these overdensities, and closely match the abundance patterns of stars in the Galactic disk. We conclude that these stars came from the disk, and that the overdensities that they are part of were created by tidal interactions of the disk with passing or merging dwarf galaxies.
Publisher: EDP Sciences
Date: 03-2010
Publisher: Oxford University Press (OUP)
Date: 23-08-2018
Publisher: EDP Sciences
Date: 25-08-2023
DOI: 10.1051/0004-6361/202346196
Abstract: Gaia EDR3 has provided unprecedented data that has generated a great deal of interest in the astrophysical community, even though systematics affect the reported parallaxes at the level of ∼10 μas. Independent distance measurements are available from asteroseismology of red-giant stars with measurable parallaxes, whose magnitude and colour ranges more closely reflect those of other stars of interest. In this paper we determine distances to nearly 12 500 red-giant-branch and red clump stars observed by Kepler , K2, and TESS. This was done via a grid-based modelling method, where global asteroseismic observables, and constraints on the photospheric chemical composition and on the unreddened photometry are used as observational inputs. This large catalogue of asteroseismic distances allows us to provide a first comparison with Gaia EDR3 parallaxes. Offset values estimated with asteroseismology show no clear trend with ecliptic latitude or magnitude, and the trend whereby they increase (in absolute terms) as we move towards redder colours is dominated by the brightest stars. The correction model proposed by Lindegren et al. (2021a) is not suitable for all the fields considered in this study. We find a good agreement between asteroseismic results and model predictions of the red clump magnitude. We discuss possible trends with the Gaia scan law statistics, and show that two magnitude regimes exist where either asteroseismology or Gaia provides the best precision in parallax.
Publisher: Oxford University Press (OUP)
Date: 13-12-2018
Publisher: Cambridge University Press (CUP)
Date: 08-2016
DOI: 10.1017/S1743921315009825
Abstract: While in external or high-redshift galaxies we can only measure integrated stellar properties at best, the Milky Way offers us the unique opportunity to study its in idual baryonic components, including stars. We use oscillations measured in red giant stars by the Kepler satellite to derive stellar ages and explore the vertical age structure across few kpc of the Milky Way disc. We find that old stars dominate at increasing Galactic heights, whereas closer to the plane a rich zoology of ages exists. The age distribution of stars shows a smooth distribution over the last 10 Gyr, which together with a flat age-metallicity relation is consistent with a quiescent evolution for the Milky Way disc since a redshift of about two.
Publisher: Apollo - University of Cambridge Repository
Date: 2017
DOI: 10.17863/CAM.11543
Publisher: EDP Sciences
Date: 08-2016
Publisher: Oxford University Press (OUP)
Date: 12-11-2020
Abstract: We present isochrone ages and initial bulk metallicities ($\\rm [Fe/H]_{bulk}$, by accounting for diffusion) of 163 722 stars from the GALAH Data Release 2, mainly composed of main-sequence turn-off stars and subgiants ($7000\\, \\mathrm{ K}& T_{\\mathrm{ eff}}& 4000\\, \\mathrm{ K}$ and $\\log g& $ dex). The local age–metallicity relationship (AMR) is nearly flat but with significant scatter at all ages the scatter is even higher when considering the observed surface abundances. After correcting for selection effects, the AMR appears to have intrinsic structures indicative of two star formation events, which we speculate are connected to the thin and thick discs in the solar neighbourhood. We also present abundance ratio trends for 16 elements as a function of age, across different $\\rm [Fe/H]_{bulk}$ bins. In general, we find the trends in terms of [X/Fe] versus age from our far larger s le to be compatible with studies based on small (∼100 stars) s les of solar twins, but we now extend them to both sub- and supersolar metallicities. The α-elements show differing behaviour: the hydrostatic α-elements O and Mg show a steady decline with time for all metallicities, while the explosive α-elements Si, Ca, and Ti are nearly constant during the thin-disc epoch (ages $\\lesssim \\! 12$ Gyr). The s-process elements Y and Ba show increasing [X/Fe] with time while the r-process element Eu has the opposite trend, thus favouring a primary production from sources with a short time delay such as core-collapse supernovae over long-delay events such as neutron star mergers.
Publisher: American Astronomical Society
Date: 21-09-2018
Publisher: Oxford University Press (OUP)
Date: 07-12-2007
Publisher: Oxford University Press (OUP)
Date: 06-01-2021
Abstract: The metal-poor stars in the bulge are important relics of the Milky Way’s formation history, as simulations predict that they are some of the oldest stars in the Galaxy. In order to determine if they are truly ancient stars, we must understand their origins. Currently, it is unclear if the metal-poor stars in the bulge ([Fe/H] & −1 dex) are merely halo interlopers, a unique accreted population, part of the boxy eanut-shaped bulge, or a classical bulge population. In this work, we use spectra from the VLT/FLAMES spectrograph to obtain metallicity estimates using the Ca-II triplet of 473 bulge stars (187 of which have [Fe/H] & −1 dex), targeted using SkyMapper photometry. We also use Gaia DR2 data to infer the Galactic positions and velocities along with orbital properties for 523 stars. We employ a probabilistic orbit analysis and find that about half of our s le has a & per cent probability of being bound to the bulge, and half are halo interlopers. We also see that the occurrence rate of halo interlopers increases steadily with decreasing metallicity across the full range of our s le (−3 & [Fe/H] & 0.5). Our examination of the kinematics of the confined compared to the unbound stars indicates the metal-poor bulge comprises at least two populations those confined to the boxy eanut bulge and halo stars passing through the inner galaxy. We conclude that an orbital analysis approach, as we have employed, is important to understand the composite nature of the metal-poor stars in the inner region.
Publisher: American Astronomical Society
Date: 18-05-2012
Publisher: American Astronomical Society
Date: 02-2022
Abstract: We present the third and final data release of the K2 Galactic Archaeology Program (K2 GAP) for C aigns C1–C8 and C10–C18. We provide asteroseismic radius and mass coefficients, κ R and κ M , for ∼19,000 red giant stars, which translate directly to radius and mass given a temperature. As such, K2 GAP DR3 represents the largest asteroseismic s le in the literature to date. K2 GAP DR3 stellar parameters are calibrated to be on an absolute parallactic scale based on Gaia DR2, with red giant branch and red clump evolutionary state classifications provided via a machine-learning approach. Combining these stellar parameters with GALAH DR3 spectroscopy, we determine asteroseismic ages with precisions of ∼20%–30% and compare age-abundance relations to Galactic chemical evolution models among both low- and high- α populations for α , light, iron-peak, and neutron-capture elements. We confirm recent indications in the literature of both increased Ba production at late Galactic times as well as significant contributions to r -process enrichment from prompt sources associated with, e.g., core-collapse supernovae. With an eye toward other Galactic archeology applications, we characterize K2 GAP DR3 uncertainties and completeness using injection tests, suggesting that K2 GAP DR3 is largely unbiased in mass/age, with uncertainties of 2.9% (stat.) ± 0.1% (syst.) and 6.7% (stat.) ± 0.3% (syst.) in κ R and κ M for red giant branch stars and 4.7% (stat.) ± 0.3% (syst.) and 11% (stat.) ± 0.9% (syst.) for red clump stars. We also identify percent-level asteroseismic systematics, which are likely related to the time baseline of the underlying data, and which therefore should be considered in TESS asteroseismic analysis.
Publisher: Oxford University Press (OUP)
Date: 15-02-2014
DOI: 10.1093/MNRAS/STU089
Publisher: EDP Sciences
Date: 07-2017
Publisher: Oxford University Press (OUP)
Date: 12-12-2012
DOI: 10.1093/MNRAS/STS345
Start Date: 2018
End Date: 2019
Funder: Deutsche Forschungsgemeinschaft
View Funded ActivityStart Date: 2022
End Date: 2023
Funder: Australian Research Council
View Funded ActivityStart Date: 2019
End Date: 2019
Funder: Australian Research Council
View Funded ActivityStart Date: 11-2022
End Date: 11-2024
Amount: $770,000.00
Funder: Australian Research Council
View Funded ActivityStart Date: 05-2015
End Date: 06-2020
Amount: $385,100.00
Funder: Australian Research Council
View Funded ActivityStart Date: 06-2017
End Date: 07-2023
Amount: $681,054.00
Funder: Australian Research Council
View Funded ActivityStart Date: 2019
End Date: 12-2020
Amount: $159,000.00
Funder: Australian Research Council
View Funded Activity