ORCID Profile
0000-0003-2644-135X
Current Organisation
The University of Edinburgh
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Astronomical and Space Sciences | Pattern Recognition and Data Mining | Galactic Astronomy | Cosmology and Extragalactic Astronomy
Publisher: EDP Sciences
Date: 10-2014
Publisher: American Astronomical Society
Date: 08-2018
Publisher: EDP Sciences
Date: 24-01-2017
Publisher: American Astronomical Society
Date: 03-03-2023
Abstract: We describe the spectroscopic data processing pipeline of the Dark Energy Spectroscopic Instrument (DESI), which is conducting a redshift survey of about 40 million galaxies and quasars using a purpose-built instrument on the 4 m Mayall Telescope at Kitt Peak National Observatory. The main goal of DESI is to measure with unprecedented precision the expansion history of the universe with the baryon acoustic oscillation technique and the growth rate of structure with redshift space distortions. Ten spectrographs with three cameras each disperse the light from 5000 fibers onto 30 CCDs, covering the near-UV to near-infrared (3600–9800 Å) with a spectral resolution ranging from 2000 to 5000. The DESI data pipeline generates wavelength- and flux-calibrated spectra of all the targets, along with spectroscopic classifications and redshift measurements. Fully processed data from each night are typically available to the DESI collaboration the following morning. We give details about the pipeline’s algorithms, and provide performance results on the stability of the optics, the quality of the sky background subtraction, and the precision and accuracy of the instrumental calibration. This pipeline has been used to process the DESI Survey Validation data set, and has exceeded the project’s requirements for redshift performance, with high efficiency and a purity greater than 99% for all target classes.
Publisher: Oxford University Press (OUP)
Date: 27-09-2016
Publisher: Oxford University Press (OUP)
Date: 23-01-2018
DOI: 10.1093/MNRAS/STY170
Publisher: Oxford University Press (OUP)
Date: 20-02-2023
Abstract: We present a 6D map of the Orphan–Chenab (OC) stream by combining the data from Southern Stellar Stream Spectroscopic Survey (S5) and Gaia. We reconstruct the proper motion, radial velocity, distance, on-sky track, and stellar density along the stream with spline models. The stream has a total luminosity of MV = −8.2 and metallicity of [Fe/H] = −1.9, similar to classical Milky Way (MW) satellites like Draco. The stream shows drastic changes in its physical width varying from 200 pc to 1 kpc, but a constant line-of-sight velocity dispersion of 5 $\\mathrm{km\\, s^{-1}}$. Despite the large apparent variation in the stellar number density along the stream, the flow rate of stars along the stream is remarkably constant. We model the 6D stream track by a Lagrange-point stripping method with a flexible MW potential in the presence of a moving extended Large Magellanic Cloud (LMC). This allows us to constrain the mass profile of the MW within the distance range 15.6 & r & 55.5 kpc, with the best measured enclosed mass of $(2.85\\pm 0.1)\\times 10^{11}\\, \\mathrm{\\, M_\\odot }$ within 32.4 kpc. Our stream measurements are highly sensitive to the LMC mass profile with the most precise measurement of its enclosed mass made at 32.8 kpc, $(7.02\\pm 0.9)\\times 10^{10}\\, {\\rm M}_\\odot$. We also detect that the LMC dark matter halo extends to at least 53 kpc. The fitting of the OC stream allows us to constrain the past LMC trajectory and the degree of dynamical friction it experienced. We demonstrate that the stars in the OC stream show large energy and angular momentum spreads caused by LMC perturbation.
Publisher: EDP Sciences
Date: 05-2014
Publisher: EDP Sciences
Date: 13-06-2016
Publisher: American Astronomical Society
Date: 24-09-2020
Publisher: EDP Sciences
Date: 17-06-2016
Publisher: EDP Sciences
Date: 05-2017
Publisher: EDP Sciences
Date: 09-2019
DOI: 10.1051/0004-6361/201935282
Abstract: Context . In the era of large high-resolution spectroscopic surveys such as Gaia -ESO and APOGEE, high-quality spectra can contribute to our understanding of the Galactic chemical evolution by providing abundances of elements that belong to the different nucleosynthesis channels, and also by providing constraints to one of the most elusive astrophysical quantities: stellar age. Aims . Some abundance ratios, such as [C/N], have been proven to be excellent indicators of stellar ages. We aim at providing an empirical relationship between stellar ages and [C/N] using open star clusters, observed by the Gaia -ESO and APOGEE surveys, as calibrators. Methods . We used stellar parameters and abundances from the Gaia -ESO Survey and APOGEE Survey of the Galactic field and open cluster stars. Ages of star clusters were retrieved from the literature sources and validated using a common set of isochrones. We used the same isochrones to determine for each age and metallicity the surface gravity at which the first dredge-up and red giant branch bump occur. We studied the effect of extra-mixing processes in our s le of giant stars, and we derived the mean [C/N] in evolved stars, including only stars without evidence of extra mixing. By combining the Gaia -ESO and APOGEE s les of open clusters, we derived a linear relationship between [C/N] and (logarithmic) cluster ages. Results . We apply our relationship to selected giant field stars in the Gaia -ESO and APOGEE surveys. We find an age separation between thin- and thick-disc stars and age trends within their populations, with an increasing age towards lower metallicity populations. Conclusions . With this empirical relationship, we are able to provide an age estimate for giant stars in which C and N abundances are measured. For giant stars, the isochrone fitting method is indeed less sensitive than for dwarf stars at the turn-off. Our method can therefore be considered as an additional tool to give an independent estimate of the age of giant stars. The uncertainties in their ages is similar to those obtained using isochrone fitting for dwarf stars.
Publisher: Oxford University Press (OUP)
Date: 22-03-2022
Abstract: We explore the structural and kinematic properties of the outskirts of the Large Magellanic Cloud (LMC) using data from the Magellanic Edges Survey (MagES) and Gaia EDR3. Even at large galactocentric radii (8° & R & 11°), we find the north-eastern LMC disc is relatively unperturbed: its kinematics are consistent with a disc of inclination ∼36.5° and line-of-nodes position angle ∼145° east of north. In contrast, fields at similar radii in the southern and western disc are significantly perturbed from equilibrium, with non-zero radial and vertical velocities, and distances significantly in front of the disc plane implied by our north-eastern fields. We compare our observations to simple dynamical models of the Magellanic or Milky Way system which describe the LMC as a collection of tracer particles within a rigid potential, and the Small Magellanic Cloud (SMC) as a rigid Hernquist potential. A possible SMC crossing of the LMC disc plane ∼400 Myr ago, in combination with the LMC’s infall to the Milky Way potential, can qualitatively explain many of the perturbations in the outer disc. Additionally, we find the claw-like and arm-like structures south of the LMC have similar metallicities to the outer LMC disc ([Fe/H] ∼ −1), and are likely comprised of perturbed LMC disc material. The claw-like substructure is particularly disturbed, with out-of-plane velocities & km s−1 and apparent counter-rotation relative to the LMC’s disc motion. More detailed N-body models are necessary to elucidate the origin of these southern features, potentially requiring repeated interactions with the SMC prior to ∼1 Gyr ago.
Publisher: American Astronomical Society
Date: 20-03-2006
DOI: 10.1086/499931
Publisher: EDP Sciences
Date: 09-2018
DOI: 10.1051/0004-6361/201832841
Abstract: Context . Several works have found an increase of the abundances of the s -process neutron-capture elements in the youngest Galactic stellar populations. These trends provide important constraints on stellar and Galactic evolution and they need to be confirmed with large and statistically significant s les of stars spanning wide age and distance intervals. Aims . We aim to trace the abundance patterns and the time evolution of five s -process elements – two belonging to the first peak, Y and Zr, and three belonging to the second peak, Ba, La, and Ce – using the Gaia -ESO IDR 5 results for open clusters and disc stars. Methods . From the UVES spectra of cluster member stars, we determined the average composition of clusters with ages .1 Gyr. We derived statistical ages and distances of field stars, and we separated them into thin and thick disc populations. We studied the time-evolution and dependence on metallicity of abundance ratios using open clusters and field stars whose parameters and abundances were derived in a homogeneous way. Results . Using our large and homogeneous s le of open clusters, thin and thick disc stars, spanning an age range larger than 10 Gyr, we confirm an increase towards young ages of s -process abundances in the solar neighbourhood. These trends are well defined for open clusters and stars located nearby the solar position and they may be explained by a late enrichment due to significant contribution to the production of these elements from long-living low-mass stars. At the same time, we find a strong dependence of the s -process abundance ratios on the Galactocentric distance and on the metallicity of the clusters and field stars. Conclusions . Our results, derived from the largest and most homogeneous s le of s -process abundances in the literature, confirm the growth with decreasing stellar ages of the s -process abundances in both field and open cluster stars. At the same time, taking advantage of the abundances of open clusters located in a wide Galactocentric range, these results offer a new perspective on the dependence of the s -process evolution on the metallicity and star formation history, pointing to different behaviours at various Galactocentric distances.
Publisher: Oxford University Press (OUP)
Date: 04-11-2019
Abstract: We present the serendipitous discovery of the fastest main-sequence hyper-velocity star (HVS) by the Southern Stellar Stream Spectroscopic Survey (S5). The star S5-HVS1 is a ∼2.35 M⊙ A-type star located at a distance of ∼9 kpc from the Sun and has a heliocentric radial velocity of 1017 ± 2.7 $\\mathrm{\\, km\\, s^{-1}}$ without any signature of velocity variability. The current 3D velocity of the star in the Galactic frame is 1755 ± 50 $\\mathrm{\\, km\\, s^{-1}}$. When integrated backwards in time, the orbit of the star points unambiguously to the Galactic Centre, implying that S5-HVS1 was kicked away from Sgr A* with a velocity of ∼1800 $\\mathrm{\\, km\\, s^{-1}}$ and travelled for 4.8 Myr to its current location. This is so far the only HVS confidently associated with the Galactic Centre. S5-HVS1 is also the first hyper-velocity star to provide constraints on the geometry and kinematics of the Galaxy, such as the Solar motion Vy,⊙ = 246.1 ± 5.3 $\\mathrm{\\, km\\, s^{-1}}$ or position R0 = 8.12 ± 0.23 kpc. The ejection trajectory and transit time of S5-HVS1 coincide with the orbital plane and age of the annular disc of young stars at the Galactic Centre, and thus may be linked to its formation. With the S5-HVS1 ejection velocity being almost twice the velocity of other hyper-velocity stars previously associated with the Galactic Centre, we question whether they have been generated by the same mechanism or whether the ejection velocity distribution has been constant over time.
Publisher: American Astronomical Society
Date: 04-05-2017
Publisher: American Astronomical Society
Date: 03-2022
Abstract: We report the kinematic, orbital, and chemical properties of 12 stellar streams with no evident progenitors using line-of-sight velocities and metallicities from the Southern Stellar Stream Spectroscopic Survey ( S 5 ), proper motions from Gaia EDR3, and distances derived from distance tracers or the literature. This data set provides the largest homogeneously analyzed set of streams with full 6D kinematics and metallicities. All streams have heliocentric distances between ∼10 and 50 kpc. The velocity and metallicity dispersions show that half of the stream progenitors were disrupted dwarf galaxies (DGs), while the other half originated from disrupted globular clusters (GCs), hereafter referred to as DG and GC streams. Based on the mean metallicities of the streams and the mass–metallicity relation, the luminosities of the progenitors of the DG streams range between those of Carina and Ursa Major I (−9.5 ≲ M V ≲ −5.5). Four of the six GC streams have mean metallicities of [Fe/H] −2, more metal poor than typical Milky Way (MW) GCs at similar distances. Interestingly, the 300S and Jet GC streams are the only streams on retrograde orbits in our dozen-stream s le. Finally, we compare the orbital properties of the streams with known DGs and GCs in the MW, finding several possible associations. Some streams appear to have been accreted with the recently discovered Gaia–Enceladus–Sausage system, and others suggest that GCs were formed in and accreted together with the progenitors of DG streams whose stellar masses are similar to those of Draco to Carina (∼10 5 –10 6 M ⊙ ).
Publisher: American Astronomical Society
Date: 24-10-2019
Publisher: Oxford University Press (OUP)
Date: 29-04-2016
Publisher: Oxford University Press (OUP)
Date: 03-10-2019
Abstract: We introduce the southern stellar stream spectroscopy survey (S5), an on-going program to map the kinematics and chemistry of stellar streams in the southern hemisphere. The initial focus of S5 has been spectroscopic observations of recently identified streams within the footprint of the dark energy survey (DES), with the eventual goal of surveying streams across the entire southern sky. Stellar streams are composed of material that has been tidally striped from dwarf galaxies and globular clusters and hence are excellent dynamical probes of the gravitational potential of the Milky Way, as well as providing a detailed snapshot of its accretion history. Observing with the 3.9 m Anglo-Australian Telescope’s 2-degree-Field fibre positioner and AAOmega spectrograph, and combining the precise photometry of DES DR1 with the superb proper motions from Gaia DR2, allows us to conduct an efficient spectroscopic survey to map these stellar streams. So far S5 has mapped nine DES streams and three streams outside of DES the former are the first spectroscopic observations of these recently discovered streams. In addition to the stream survey, we use spare fibres to undertake a Milky Way halo survey and a low-redshift galaxy survey. This paper presents an overview of the S5 program, describing the scientific motivation for the survey, target selection, observation strategy, data reduction, and survey validation. Finally, we describe early science results on stellar streams and Milky Way halo stars drawn from the survey. Updates on S5, including future public data releases, can be found at s5collab.github.io.
Publisher: Oxford University Press (OUP)
Date: 24-12-2016
Publisher: Oxford University Press (OUP)
Date: 04-03-2022
Abstract: We measure rotational broadening in spectra taken by the Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey to characterize the relationship between stellar multiplicity and rotation. We create a s le of 2786 giants and 24 496 dwarfs with stellar parameters and multiple radial velocities from the APOGEE pipeline, projected rotation speeds vsin i determined from our own pipeline, and distances, masses, and ages measured by Sanders & Das. We use the statistical distribution of the maximum shift in the radial velocities, ΔRVmax, as a proxy for the close binary fraction to explore the interplay between stellar evolution, rotation, and multiplicity. Assuming that the minimum orbital period allowed is the critical period for Roche Lobe overflow and rotational synchronization, we calculate theoretical upper limits on expected vsin i and ΔRVmax values. These expectations agree with the positive correlation between the maximum ΔRVmax and vsin i values observed in our s le as a function of log(g). We find that the fast rotators in our s le have a high occurrence of short-period [log(P/d) ≲ 4] companions. We also find that old, rapidly rotating main-sequence stars have larger completeness-corrected close binary fractions than their younger peers. Furthermore, rapidly rotating stars with large ΔRVmax consistently show differences of 1–10 Gyr between the predicted gyrochronological and measured isochronal ages. These results point towards a link between rapid rotation and close binarity through tidal interactions. We conclude that stellar rotation is strongly correlated with stellar multiplicity in the field, and caution should be taken in the application of gyrochronology relations to cool stars.
Publisher: American Astronomical Society
Date: 02-2023
Abstract: We present Dark Energy Spectroscopic Instrument (DESI) observations of the inner halo of M31, which reveal the kinematics of a recent merger—a galactic immigration event—in exquisite detail. Of the 11,416 sources studied in 3.75 hr of on-sky exposure time, 7438 are M31 sources with well-measured radial velocities. The observations reveal intricate coherent kinematic structure in the positions and velocities of in idual stars: streams, wedges, and chevrons. While hints of coherent structures have been previously detected in M31, this is the first time they have been seen with such detail and clarity in a galaxy beyond the Milky Way. We find clear kinematic evidence for shell structures in the Giant Stellar Stream, the Northeast Shelf, and Western Shelf regions. The kinematics are remarkably similar to the predictions of dynamical models constructed to explain the spatial morphology of the inner halo. The results are consistent with the interpretation that much of the substructure in the inner halo of M31 is produced by a single galactic immigration event 1–2 Gyr ago. Significant numbers of metal-rich stars ([Fe/H] − 0.5) are present in all of the detected substructures, suggesting that the immigrating galaxy had an extended star formation history. We also investigate the ability of the shells and Giant Stellar Stream to constrain the gravitational potential of M31, and estimate the mass within a projected radius of 125 kpc to be log 10 M NFW ( 125 kpc ) / M ⊙ = 11.80 − 0.10 + 0.12 . The results herald a new era in our ability to study stars on a galactic scale and the immigration histories of galaxies.
Publisher: Springer Science and Business Media LLC
Date: 29-07-2020
Publisher: EDP Sciences
Date: 07-2017
Publisher: Oxford University Press (OUP)
Date: 20-05-2016
Publisher: American Astronomical Society
Date: 21-08-2020
Abstract: We present the serendipitous discovery of a low optical-luminosity nova occurring in a D-type symbiotic binary star system in the Milky Way. We lay out the extensive archival data alongside new follow-up observations related to the stellar object CN Cha in the constellation of Chamaeleon. The object had long period (250 days), high litude (3 mag) optical variability in its recent past, preceding an increase in optical brightness by 8 magnitudes and a persistence at this brightness for about 3 yr, followed by a period of 1.4 mag yr −1 dimming. The object’s current optical luminosity seems to be dominated by H α emission, which also exhibits blueshifted absorption (a P-Cygni-like profile). After consideration of a number of theories to explain these myriad observations, we determine that CN Cha is most likely a symbiotic (an evolved-star–white-dwarf binary) system that has undergone a long-duration, low optical brightness, nova, placing it squarely in the class of so-called “slow novae,” of which there are only a few known ex les. The duration of the optical plateau in CN Cha would make it the shortest timescale plateau of any known slow symbiotic novae.
Publisher: EDP Sciences
Date: 07-2018
DOI: 10.1051/0004-6361/201832645
Abstract: Context. The origin and dynamical evolution of star clusters is an important topic in stellar astrophysics. Several models have been proposed in order to understand the formation of bound and unbound clusters and their evolution, and they can be tested by examining the kinematical and dynamical properties of clusters over a wide range of ages and masses. Aims. We use the Gaia -ESO Survey products to study four open clusters (IC 2602, IC 2391, IC 4665, and NGC 2547) that lie in the age range between 20 and 50 Myr. Methods. We employ the gravity index γ and the equivalent width of the lithium line at 6708 Å together with effective temperature T eff and the metallicity of the stars in order to discard observed contaminant stars. Then we derive the cluster radial velocity dispersions σ c , the total cluster mass M tot , and the half mass radius r hm . Using the Gaia -DR1 TGAS catalogue, we independently derive the intrinsic velocity dispersion of the clusters from the astrometric parameters of cluster members. Results. The intrinsic radial velocity dispersions derived by the spectroscopic data are higher than those derived from the TGAS data, possibly due to the different masses of the considered stars. Using M tot and r hm we derive the virial velocity dispersion σ vir and we find that three out of four clusters are supervirial. This result is in agreement with the hypothesis that these clusters are dispersing, as predicted by the “residual gas expulsion” scenario. However, recent simulations show that the virial ratio of young star clustersmay be overestimated if it is determined using the global velocity dispersion, since the clusters are not fully relaxed.
Publisher: EDP Sciences
Date: 16-05-2016
Publisher: American Astronomical Society
Date: 21-09-2015
Publisher: American Astronomical Society
Date: 04-2023
Abstract: We describe the Milky Way Survey (MWS) that will be undertaken with the Dark Energy Spectroscopic Instrument (DESI) on the Mayall 4 m telescope at the Kitt Peak National Observatory. Over the next 5 yr DESI MWS will observe approximately seven million stars at Galactic latitudes ∣ b ∣ 20°, with an inclusive target selection scheme focused on the thick disk and stellar halo. MWS will also include several high-completeness s les of rare stellar types, including white dwarfs, low-mass stars within 100 pc of the Sun, and horizontal branch stars. We summarize the potential of DESI to advance understanding of the Galactic structure and stellar evolution. We introduce the final definitions of the main MWS target classes and estimate the number of stars in each class that will be observed. We describe our pipelines for deriving radial velocities, atmospheric parameters, and chemical abundances. We use ≃500,000 spectra of unique stellar targets from the DESI Survey Validation program (SV) to demonstrate that our pipelines can measure radial velocities to ≃1 km s −1 and [Fe/H] accurate to ≃0.2 dex for typical stars in our main s le. We find the stellar parameter distributions from ≈100 deg 2 of SV observations with ≳90% completeness on our main s le are in good agreement with expectations from mock catalogs and previous surveys.
Publisher: EDP Sciences
Date: 07-2014
Publisher: EDP Sciences
Date: 2018
DOI: 10.1051/0004-6361/201730412
Abstract: Context. There have been conflicting results with respect to the extent that radial migration has played in the evolution of the Galaxy. Additionally, observations of the solar neighborhood have shown evidence of a merger in the past history of the Milky Way that drives enhanced radial migration. Aims. We attempt to determine the relative fraction of stars that have undergone significant radial migration by studying the orbital properties of metal-rich ([Fe/H] 0.1) stars within 2 kpc of the Sun. We also aim to investigate the kinematic properties, such as velocity dispersion and orbital parameters, of stellar populations near the Sun as a function of [Mg/Fe] and [Fe/H], which could show evidence of a major merger in the past history of the Milky Way. Methods. We used a s le of more than 3000 stars selected from the fourth internal data release of the Gaia -ESO Survey. We used the stellar parameters from the Gaia -ESO Survey along with proper motions from PPMXL to determine distances, kinematics, and orbital properties for these stars to analyze the chemodynamic properties of stellar populations near the Sun. Results. Analyzing the kinematics of the most metal-rich stars ([Fe/H] 0.1), we find that more than half have small eccentricities ( e 0.2) or are on nearly circular orbits. Slightly more than 20% of the metal-rich stars have perigalacticons R p 7 kpc. We find that the highest [Mg/Fe], metal-poor populations have lower vertical and radial velocity dispersions compared to lower [Mg/Fe] populations of similar metallicity by ~10 km s -1 . The median eccentricity increases linearly with [Mg/Fe] across all metallicities, while the perigalacticon decreases with increasing [Mg/Fe] for all metallicities. Finally, the most [Mg/Fe]-rich stars are found to have significant asymmetric drift and rotate more than 40 km s -1 slower than stars with lower [Mg/Fe] ratios. Conclusions. While our results cannot constrain how far stars have migrated, we propose that migration processes are likely to have played an important role in the evolution of the Milky Way, with metal-rich stars migrating from the inner disk toward to solar neighborhood and past mergers potentially driving enhanced migration of older stellar populations in the disk.
Publisher: EDP Sciences
Date: 03-2015
Publisher: Oxford University Press (OUP)
Date: 24-04-2018
Publisher: American Astronomical Society
Date: 05-2023
Abstract: Stellar streams in the Galactic halo are useful probes of the assembly of galaxies like the Milky Way. Many tidal stellar streams that have been found in recent years are accompanied by a known progenitor globular cluster or dwarf galaxy. However, the Orphan–Chenab (OC) stream is one case where a relatively narrow stream of stars has been found without a known progenitor. In an effort to find the parent of the OC stream, we use astrometry from the early third data release of ESA’s Gaia mission (Gaia EDR3) and radial velocity information from the Sloan Digital Sky Survey (SDSS)-IV Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey to find up to 13 stars that are likely members of the OC stream. We use the APOGEE survey to study the chemical nature (for up to 10 stars) of the OC stream in the α (O, Mg, Ca, Si, Ti, and S), odd- Z (Al, K, and V), Fe-peak (Fe, Ni, Mn, Co, and Cr), and neutron-capture (Ce) elemental groups. We find that the stars that make up the OC stream are not consistent with a monometallic population and have a median metallicity of −1.92 dex with a dispersion of 0.28 dex. Our results also indicate that the α elements are depleted compared to the known Milky Way populations and that its [Mg/Al] abundance ratio is not consistent with second-generation stars from globular clusters. The detailed chemical pattern of these stars, namely the [ α /Fe]–[Fe/H] plane and the metallicity distribution, indicates that the OC stream progenitor is very likely to be a dwarf spheroidal galaxy with a mass of ∼10 6 M ⊙ .
Publisher: Oxford University Press (OUP)
Date: 25-11-2021
Abstract: The highly-substructured outskirts of the Magellanic Clouds provide ideal locations for studying the complex interaction history between both Clouds and the Milky Way (MW). In this paper, we investigate the origin of a & ° long arm-like feature in the northern outskirts of the Large Magellanic Cloud (LMC) using data from the Magellanic Edges Survey (MagES) and Gaia EDR3. We find that the arm has a similar geometry and metallicity to the nearby outer LMC disc, indicating that it is comprised of perturbed disc material. Whilst the azimuthal velocity and velocity dispersions along the arm are consistent with those in the outer LMC, the in-plane radial velocity and out-of-plane vertical velocity are significantly perturbed from equilibrium disc kinematics. We compare these observations to a new suite of dynamical models of the Magellanic/MW system, which describe the LMC as a collection of tracer particles within a rigid potential, and the SMC as a rigid Hernquist potential. Our models indicate the tidal force of the MW during the LMC’s infall is likely responsible for the observed increasing out-of-plane velocity along the arm. Our models also suggest close LMC/SMC interactions within the past Gyr, particularly the SMC’s pericentric passage ∼150 Myr ago and a possible SMC crossing of the LMC disc plane ∼400 Myr ago, likely do not perturb stars that today comprise the arm. Historical interactions with the SMC prior to ∼1 Gyr ago may be required to explain some of the observed kinematic properties of the arm, in particular its strongly negative in-plane radial velocity.
Publisher: Oxford University Press (OUP)
Date: 05-07-2018
Publisher: EDP Sciences
Date: 10-2015
Publisher: American Astronomical Society
Date: 25-05-2023
Abstract: We present the first detailed comparison of populations of dwarf galaxy stellar streams in cosmological simulations and the Milky Way. In particular, we compare streams identified around 13 Milky Way analogs in the FIRE-2 simulations to streams observed by the Southern Stellar Stream Spectroscopic Survey ( S 5 ). For an accurate comparison, we produce mock Dark Energy Survey (DES) observations of the FIRE streams and estimate the detectability of their tidal tails and progenitors. The number and stellar mass distributions of detectable stellar streams is consistent between observations and simulations. However, there are discrepancies in the distributions of pericenters and apocenters, with the detectable FIRE streams, on average, forming at larger pericenters (out to kpc) and surviving only at larger apocenters (≳40 kpc) than those observed in the Milky Way. We find that the population of high-stellar-mass dwarf galaxy streams in the Milky Way is incomplete. Interestingly, a large fraction of the FIRE streams would only be detected as intact satellites in DES-like observations, since their tidal tails have too low surface brightness to be detectable. We thus predict a population of yet-undetected tidal tails around Milky Way satellites, as well as a population of fully undetected low-surface-brightness stellar streams, and estimate their detectability with the Rubin Observatory. Finally, we discuss the causes and implications of the discrepancies between the stream populations in FIRE and the Milky Way, and explore future avenues for tests of satellite disruption in cosmological simulations.
Publisher: Oxford University Press (OUP)
Date: 14-03-2016
DOI: 10.1093/MNRAS/STW497
Publisher: Oxford University Press (OUP)
Date: 11-09-2017
Publisher: American Astronomical Society
Date: 10-06-2008
DOI: 10.1086/588032
Publisher: Oxford University Press (OUP)
Date: 14-01-2021
Abstract: Until the recent advent of Gaia Data Release 2 (DR2) and deep multi-object spectroscopy, it has been difficult to obtain 6D phase space information for large numbers of stars beyond 4 kpc, in particular towards the Galactic Centre, where dust and crowding are significant. We combine line-of-sight velocities from the Abundances and Radial velocity Galactic Origins Survey (ARGOS) with proper motions from Gaia DR2 to obtain a s le of ∼7000 red clump stars with 3D velocities. We perform a large-scale stellar kinematics study of the Milky Way bulge to characterize the bulge velocity ellipsoids in 20 fields. The tilt of the major-axis of the velocity ellipsoid in the radial-longitudinal velocity plane, or vertex deviation, is characteristic of non-axisymmetric systems and a significant tilt is a robust indicator of non-axisymmetry or bar presence. We compare the observations to the predicted kinematics of an N-body boxy-bulge model formed from dynamical instabilities. In the model, the lv values are strongly correlated with the angle (α) between the bulge major-axis and the Sun-Galactic centre line of sight. We use a maximum likelihood method to obtain an independent measurement of α, from bulge stellar kinematics alone, performing a robust error analysis. The most likely value of α given our model is α = (29 ± 3)○, with an additional systematic uncertainty due to comparison with one specific model. In Baade’s window, the metal-rich stars display a larger vertex deviation (lv = −40○) than the metal-poor stars (lv = 10○) but we do not detect significant lv−metallicity trends in the other fields.
Publisher: Oxford University Press (OUP)
Date: 02-2017
DOI: 10.1093/MNRAS/STX263
Publisher: American Astronomical Society
Date: 28-10-2021
Publisher: Oxford University Press (OUP)
Date: 28-10-2022
Abstract: It has recently been shown that the Large Magellanic Cloud (LMC) has a substantial effect on the Milky Way’s stellar halo and stellar streams. Here, we explore how deformations of the Milky Way and LMC’s dark matter haloes affect stellar streams, and whether these effects are observable. In particular, we focus on the Orphan–Chenab (OC) stream which passes particularly close to the LMC and spans a large portion of the Milky Way’s halo. We represent the Milky Way–LMC system using basis function expansions that capture their evolution in an N-body simulation. We present the properties of this system, such as the evolution of the densities and force fields of each galaxy. The OC stream is evolved in this time-dependent, deforming potential, and we investigate the effects of the various moments of the Milky Way and the LMC. We find that the simulated OC stream is strongly influenced by the deformations of both the Milky Way and the LMC and that this effect is much larger than current observational errors. In particular, the Milky Way dipole has the biggest impact on the stream, followed by the evolution of the LMC’s monopole, and the LMC’s quadrupole. Detecting these effects would confirm a key prediction of collisionless, cold dark matter, and would be a powerful test of alternative dark matter and alternative gravity models.
Publisher: Oxford University Press (OUP)
Date: 12-08-2017
Publisher: Oxford University Press (OUP)
Date: 17-11-2016
Publisher: EDP Sciences
Date: 11-2016
Publisher: Oxford University Press (OUP)
Date: 14-07-2020
Abstract: We present an overview of, and first science results from, the Magellanic Edges Survey (MagES), an ongoing spectroscopic survey mapping the kinematics of red clump and red giant branch stars in the highly substructured periphery of the Magellanic Clouds. In conjunction with Gaia astrometry, MagES yields a s le of ~7000 stars with in idual 3D velocities that probes larger galactocentric radii than most previous studies. We outline our target selection, observation strategy, data reduction, and analysis procedures, and present results for two fields in the northern outskirts (& ° on-sky from the centre) of the Large Magellanic Cloud (LMC). One field, located in the vicinity of an arm-like overdensity, displays apparent signatures of perturbation away from an equilibrium disc model. This includes a large radial velocity dispersion in the LMC disc plane, and an asymmetric line-of-sight velocity distribution indicative of motions vertically out of the disc plane for some stars. The second field reveals 3D kinematics consistent with an equilibrium disc, and yields Vcirc = 87.7 ± 8.0 km s−1 at a radial distance of ~10.5 kpc from the LMC centre. This leads to an enclosed mass estimate for the LMC at this radius of (1.8 ± 0.3) × 1010 M⊙.
Publisher: American Astronomical Society
Date: 08-2021
Publisher: American Astronomical Society
Date: 11-2021
Publisher: American Astronomical Society
Date: 11-05-2018
Publisher: EDP Sciences
Date: 03-2014
Publisher: American Astronomical Society
Date: 20-06-2016
Publisher: American Astronomical Society
Date: 10-2007
DOI: 10.1086/518836
Publisher: American Astronomical Society
Date: 12-2021
Abstract: Stellar streams are excellent probes of the underlying gravitational potential in which they evolve. In this work, we fit dynamical models to five streams in the Southern Galactic hemisphere, combining observations from the Southern Stellar Stream Spectroscopic Survey ( S 5 ), Gaia EDR3, and the Dark Energy Survey, to measure the mass of the Large Magellanic Cloud (LMC). With an ensemble of streams, we find a mass of the LMC ranging from ∼14–19 × 10 10 M ⊙ , probed over a range of closest approach times and distances. With the most constraining stream (Orphan–Chenab), we measure an LMC mass of 18.8 − 4.0 + 3.5 × 10 10 M ⊙ , probed at a closest approach time of 310 Myr and a closest approach distance of 25.4 kpc. This mass is compatible with previous measurements, showing that a consistent picture is emerging of the LMC’s influence on structures in the Milky Way. Using this s le of streams, we find that the LMC’s effect depends on the relative orientation of the stream and LMC at their point of closest approach. To better understand this, we present a simple model based on the impulse approximation and we show that the LMC’s effect depends both on the magnitude of the velocity kick imparted to the stream and the direction of this kick.
Publisher: EDP Sciences
Date: 07-06-2016
Publisher: SPIE
Date: 24-07-2014
DOI: 10.1117/12.2055826
Publisher: EDP Sciences
Date: 05-2017
Publisher: EDP Sciences
Date: 28-04-2017
Publisher: Oxford University Press (OUP)
Date: 23-09-2020
Abstract: We use observations from the Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey to explore the relationship between stellar parameters and multiplicity. We combine high-resolution repeat spectroscopy for 41 363 dwarf and subgiant stars with abundance measurements from the APOGEE pipeline and distances and stellar parameters derived using Gaia DR2 parallaxes from Sanders & Das to identify and characterize stellar multiples with periods below 30 yr, corresponding to ΔRVmax ≳ 3 km s−1, where ΔRVmax is the maximum APOGEE-detected shift in the radial velocities. Chemical composition is responsible for most of the variation in the close binary fraction in our s le, with stellar parameters like mass and age playing a secondary role. In addition to the previously identified strong anticorrelation between the close binary fraction and [Fe/H], we find that high abundances of α elements also suppress multiplicity at most values of [Fe/H] s led by APOGEE. The anticorrelation between α abundances and multiplicity is substantially steeper than that observed for Fe, suggesting C, O, and Si in the form of dust and ices dominate the opacity of primordial protostellar discs and their propensity for fragmentation via gravitational stability. Near [Fe/H] = 0 dex, the bias-corrected close binary fraction (a & 10 au) decreases from ≈100 per cent at [α/H] = −0.2 dex to ≈15 per cent near [α/H] = 0.08 dex, with a suggestive turn-up to ≈20 per cent near [α/H] = 0.2. We conclude that the relationship between stellar multiplicity and chemical composition for sun-like dwarf stars in the field of the Milky Way is complex, and that this complexity should be accounted for in future studies of interacting binaries.
Publisher: American Astronomical Society
Date: 04-2021
Abstract: We present the first spectroscopic measurements of the ATLAS and Aliqa Uma streams from the Southern Stellar Stream Spectroscopic Survey ( S 5 ), in combination with the photometric data from the Dark Energy Survey and astrometric data from Gaia. From the coherence of spectroscopic members in radial velocity and proper motion, we find that these two systems are extremely likely to be one stream with discontinuity in morphology and density on the sky (the “kink” feature). We refer to this entire stream as the ATLAS-Aliqa Uma stream, or the AAU stream. We perform a comprehensive exploration of the effect of baryonic substructures and find that only an encounter with the Sagittarius dwarf ∼0.5 Gyr ago can create a feature similar to the observed “kink.” In addition, we also identify two gaps in the ATLAS component associated with the broadening in the stream width (the “broadening” feature). These gaps have likely been created by small mass perturbers, such as dark matter halos, as the AAU stream is the most distant cold stream known with severe variations in both the stream surface density and the stream track on the sky. With the stream track, stream distance, and kinematic information, we determine the orbit of the AAU stream and find that it has been affected by the Large Magellanic Cloud, resulting in a misalignment between the proper motion and stream track. Together with the Orphan-Chenab Stream, AAU is the second stream pair that has been found to be a single stream separated into two segments by external perturbation.
Publisher: Oxford University Press (OUP)
Date: 04-07-2016
Publisher: Oxford University Press (OUP)
Date: 18-10-2022
Abstract: We use data from the Magellanic Edges Survey (MagES) in combination with Gaia EDR3 to study the extreme southern outskirts of the Small Magellanic Cloud (SMC), focussing on a field at the eastern end of a long arm-like structure which wraps around the southern periphery of the Large Magellanic Cloud (LMC). Unlike the remainder of this structure, which is thought to be comprised of perturbed LMC disc material, the aggregate properties of the field indicate a clear connection with the SMC. We find evidence for two stellar populations in the field: one having properties consistent with the outskirts of the main SMC body, and the other significantly perturbed. The perturbed population is on average ∼0.2 dex more metal-rich, and is located ∼7 kpc in front of the dominant population with a total space velocity relative to the SMC centre of ∼230 km s−1 broadly in the direction of the LMC. We speculate on possible origins for this perturbed population, the most plausible of which is that it comprises debris from the inner SMC that has been recently tidally stripped by interactions with the LMC.
Publisher: EDP Sciences
Date: 12-2017
Publisher: Oxford University Press (OUP)
Date: 11-05-2017
Publisher: EDP Sciences
Date: 31-01-2020
DOI: 10.1051/0004-6361/201937055
Abstract: Context. Open clusters are recognised as excellent tracers of Galactic thin-disc properties. At variance with intermediate-age and old open clusters, for which a significant number of studies is now available, clusters younger than ≲150 Myr have been mostly overlooked in terms of their chemical composition until recently (with few exceptions). On the other hand, previous investigations seem to indicate an anomalous behaviour of young clusters, which includes (but is not limited to) slightly sub-solar iron (Fe) abundances and extreme, unexpectedly high barium (Ba) enhancements. Aims. In a series of papers, we plan to expand our understanding of this topic and investigate whether these chemical peculiarities are instead related to abundance analysis techniques. Methods. We present a new determination of the atmospheric parameters for 23 dwarf stars observed by the Gaia -ESO survey in five young open clusters ( τ 150 Myr) and one star-forming region (NGC 2264). We exploit a new method based on titanium (Ti) lines to derive the spectroscopic surface gravity, and most importantly, the microturbulence parameter. A combination of Ti and Fe lines is used to obtain effective temperatures. We also infer the abundances of Fe I , Fe II , Ti I , Ti II , Na I , Mg I , Al I , Si I , Ca I , Cr I , and Ni I . Results. Our findings are in fair agreement with Gaia -ESO iDR5 results for effective temperatures and surface gravities, but suggest that for very young stars, the microturbulence parameter is over-estimated when Fe lines are employed. This affects the derived chemical composition and causes the metal content of very young clusters to be under-estimated. Conclusions. Our clusters display a metallicity [Fe/H] between +0.04 ± 0.01 and +0.12 ± 0.02 they are not more metal poor than the Sun. Although based on a relatively small s le size, our explorative study suggests that we may not need to call for ad hoc explanations to reconcile the chemical composition of young open clusters with Galactic chemical evolution models.
Publisher: EDP Sciences
Date: 10-2016
Publisher: EDP Sciences
Date: 05-2017
DOI: 10.1051/0004-6361/201629160
Abstract: Context. As observational evidence steadily accumulates, the nature of the Galactic bulge has proven to be rather complex: the structural, kinematic, and chemical analyses often lead to contradictory conclusions. The nature of the metal-rich bulge – and especially of the metal-poor bulge – and their relation with other Galactic components, still need to be firmly defined on the basis of statistically significant high-quality data s les. Aims. We used the fourth internal data release of the Gaia -ESO survey to characterize the bulge metallicity distribution function (MDF), magnesium abundance, spatial distribution, and correlation of these properties with kinematics. Moreover, the homogeneous s ling of the different Galactic populations provided by the Gaia -ESO survey allowed us to perform a comparison between the bulge, thin disk, and thick disk sequences in the [Mg/Fe] vs. [Fe/H] plane in order to constrain the extent of their eventual chemical similarities. Methods. We obtained spectroscopic data for ~2500 red clump stars in 11 bulge fields, s ling the area −10° ≤ l ≤ + 8° and −10° ≤ b ≤ −4° from the fourth internal data release of the Gaia -ESO survey. A s le of ~6300 disk stars was also selected for comparison. Spectrophotometric distances computed via isochrone fitting allowed us to define a s le of stars likely located in the bulge region. Results. From a Gaussian mixture models (GMM) analysis, the bulge MDF is confirmed to be bimodal across the whole s led area. The relative ratio between the two modes of the MDF changes as a function of b , with metal-poor stars dominating at high latitudes. The metal-rich stars exhibit bar-like kinematics and display a bimodality in their magnitude distribution, a feature which is tightly associated with the X-shape bulge. They overlap with the metal-rich end of the thin disk sequence in the [Mg/Fe] vs. [Fe/H] plane. On the other hand, metal-poor bulge stars have a more isotropic hot kinematics and do not participate in the X-shape bulge. Their Mg enhancement level and general shape in the [Mg/Fe] vs. [Fe/H] plane is comparable to that of the thick disk sequence. The position at which [Mg/Fe] starts to decrease with [Fe/H], called the “knee”, is observed in the metal-poor bulge at [Fe/H] knee = −0.37 ± 0.09, being 0.06 dex higher than that of the thick disk. Although this difference is inside the error bars, it suggest a higher star formation rate (SFR) for the bulge than for the thick disk. We estimate an upper limit for this difference of Δ [Fe/H] knee = 0.24 dex. Finally, we present a chemical evolution model that suitably fits the whole bulge sequence by assuming a fast ( Gyr) intense burst of stellar formation that takes place at early epochs. Conclusions. We associate metal-rich stars with the bar boxy eanut bulge formed as the product of secular evolution of the early thin disk. On the other hand, the metal-poor subpopulation might be the product of an early prompt dissipative collapse dominated by massive stars. Nevertheless, our results do not allow us to firmly rule out the possibility that these stars come from the secular evolution of the early thick disk. This is the first time that an analysis of the bulge MDF and α -abundances has been performed in a large area on the basis of a homogeneous, fully spectroscopic analysis of high-resolution, high S/N data.
Publisher: EDP Sciences
Date: 21-04-2016
Publisher: Oxford University Press (OUP)
Date: 02-12-2014
Publisher: American Astronomical Society
Date: 07-2021
Publisher: Center for Open Science
Date: 21-10-2021
Abstract: Vaccines are a powerful and relatively safe tool to protect against a range of serious diseases. Nonetheless, a sizeable minority of people express ‘vaccination hesitancy’. Accordingly, understanding the bases of this hesitancy represents a significant public health challenge. In the present study we sought to examine the role of Big Five personality traits and general intelligence as predictors of vaccination hesitancy, across two vaccination types, in a large (N= 9667) s le of UK adults drawn from the Understanding Society longitudinal household study. We found that lower general intelligence was associated with COVID-19 and seasonal flu vaccination hesitancy, and lower neuroticism was associated with COVID-19 vaccination hesitancy. Although the self-reported reasons for being vaccine hesitant indicated a range of factors were important to people, lower general intelligence was associated with virtually all of these reasons. In contrast, Big 5 personality traits showed more nuanced patterns of association. These findings provide important insights into vaccination hesitancy and help to reconcile some of the inconsistencies found in previous literature.
Location: Germany
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
Start Date: 12-2022
End Date: 12-2025
Amount: $700,000.00
Funder: Australian Research Council
View Funded Activity