Showing papers by "Gerry Gilmore published in 2020"

Gaia Early Data Release 3: The Gaia Catalogue of Nearby Stars

Abstract: We produce a clean and well-characterised catalogue of objects within 100\,pc of the Sun from the \G\ Early Data Release 3. We characterise the catalogue through comparisons to the full data release, external catalogues, and simulations. We carry out a first analysis of the science that is possible with this sample to demonstrate its potential and best practices for its use. The selection of objects within 100\,pc from the full catalogue used selected training sets, machine-learning procedures, astrometric quantities, and solution quality indicators to determine a probability that the astrometric solution is reliable. The training set construction exploited the astrometric data, quality flags, and external photometry. For all candidates we calculated distance posterior probability densities using Bayesian procedures and mock catalogues to define priors. Any object with reliable astrometry and a non-zero probability of being within 100\,pc is included in the catalogue. We have produced a catalogue of \NFINAL\ objects that we estimate contains at least 92\% of stars of stellar type M9 within 100\,pc of the Sun. We estimate that 9\% of the stars in this catalogue probably lie outside 100\,pc, but when the distance probability function is used, a correct treatment of this contamination is possible. We produced luminosity functions with a high signal-to-noise ratio for the main-sequence stars, giants, and white dwarfs. We examined in detail the Hyades cluster, the white dwarf population, and wide-binary systems and produced candidate lists for all three samples. We detected local manifestations of several streams, superclusters, and halo objects, in which we identified 12 members of \G\ Enceladus. We present the first direct parallaxes of five objects in multiple systems within 10\,pc of the Sun.

Gaia Early Data Release 3: Structure and properties of the Magellanic Clouds

Abstract: We compare the Gaia DR2 and Gaia EDR3 performances in the study of the Magellanic Clouds and show the clear improvements in precision and accuracy in the new release. We also show that the systematics still present in the data make the determination of the 3D geometry of the LMC a difficult endeavour; this is at the very limit of the usefulness of the Gaia EDR3 astrometry, but it may become feasible with the use of additional external data. We derive radial and tangential velocity maps and global profiles for the LMC for the several subsamples we defined. To our knowledge, this is the first time that the two planar components of the ordered and random motions are derived for multiple stellar evolutionary phases in a galactic disc outside the Milky Way, showing the differences between younger and older phases. We also analyse the spatial structure and motions in the central region, the bar, and the disc, providing new insights into features and kinematics. Finally, we show that the Gaia EDR3 data allows clearly resolving the Magellanic Bridge, and we trace the density and velocity flow of the stars from the SMC towards the LMC not only globally, but also separately for young and evolved populations. This allows us to confirm an evolved population in the Bridge that is slightly shift from the younger population. Additionally, we were able to study the outskirts of both Magellanic Clouds, in which we detected some well-known features and indications of new ones.

Gaia Data Release 2 (Corrigendum)

Abstract: An error occurred during the production process of the original published version. The following names were omitted from the author list: R. Haigron, D. Hatzidimitriou, M. Hauser, M. Haywood, U. Heiter, J. Heu, T. Hilger. The original published version has been corrected together with the publication of this corrigendum.

The Gaia–ESO Survey: Carbon Abundance in the Galactic Thin and Thick Disks*

Abstract: This paper focuses on carbon, which is one of the most abundant elements in the universe and is of high importance in the field of nucleosynthesis and galactic and stellar evolution. The origin of carbon and the relative importance of massive and low-to intermediate-mass stars in producing it is still a matter of debate. We aim at better understanding the origin of carbon by studying the trends of [C/H], [C/Fe], and [C/Mg] versus [Fe/H] and [Mg/H] for 2133 FGK dwarf stars from the fifth Gaia-ESO Survey internal data release (GES iDR5). The availability of accurate parallaxes and proper motions from Gaia DR2 and radial velocities from GES iDR5 allows us to compute Galactic velocities, orbits, absolute magnitudes, and, for 1751 stars, Bayesian-derived ages. Three different selection methodologies have been adopted to discriminate between thin-and thick-disk stars. In all the cases, the two stellar groups show different [C/H], [C/Fe], and [C/Mg] and span different age intervals, with the thick-disk stars being, on average, older than the thin-disk ones. The behaviors of [C/H], [C/Fe], and [C/Mg] versus [Fe/H], [Mg/H], and age all suggest that C is primarily produced in massive stars. The increase of [C/Mg] for young thin-disk stars indicates a contribution from low-mass stars or the increased C production from massive stars at high metallicities due to the enhanced mass loss. The analysis of the orbital parameters R med and IMG ALIGN="MIDDLE" ALT="$| {Z}-{\max }| $" SRC="apjab5dc4ieqn1.gif supports an "inside-out" and "upside-down" formation scenario for the disks of the Milky Way. (Less)

The Gaia-ESO Survey: detection and characterization of single line spectroscopic binaries

Abstract: Recent and on-going large ground-based multi-object spectroscopic surveys allow to significantly increase the sample of spectroscopic binaries to get insight into their statistical properties. We investigate the repeated spectral observations of the Gaia-ESO Survey (GES) internal data release 5 to identify and characterize spectroscopic binaries with one visible component (SB1) in fields covering the discs, the bulge, the CoRot fields, and stellar clusters and associations. A statistical chi2-test is performed on spectra of the iDR5 sub-sample of approximately 43500 stars characterized by at least 2 observations and a S/N > 3. Our sample of RV variables is cleaned from contamination by pulsation/convection-induced variables using Gaia DR2 parallaxes and photometry. Monte-Carlo simulations using the SB9 catalogue of spectroscopic orbits allow to estimate our detection efficiency and to correct the SB1 rate to evaluate the GES SB1 binary fraction and its dependence with effective temperature and metallicity. We find 641 (resp., 803) FGK SB1 candidates at the 5 sigma (resp., 3 sigma) level. The orbital-period distribution is estimated from the RV standard-deviation distribution and reveals that the detected SB1 probe binaries with log(P[d]) < 4. We estimate the global GES SB1 fraction to be in the range 7-14% with a typical uncertainty of 4%. The GES SB1 frequency decreases with metallicity at a rate of -9+/-3%/dex in the metallicity range -2.7

The Gaia-ESO Survey: Oxygen Abundance in the Galactic Thin and Thick Disks*

Abstract: We analyze the oxygen abundances of a stellar sample representative of the two major Galactic populations: the thin and thick disks. The aim is to investigate the differences between members of the Galactic disks and to contribute to the understanding on the origin of oxygen chemical enrichment in the Galaxy. The analysis is based on the [O i]=6300.30 Å oxygen line in HR spectra (R ∼52,500) obtained from the GES Survey. By comparing the observed spectra with a theoretical dataset, computed in LTE with the SPECTRUM synthesis and ATLAS12 codes, we derive the oxygen abundances of 516 FGK dwarfs for which we have previously measured carbon abundances. Based on kinematic, chemical and dynamical considerations we identify 20 thin and 365 thick disk members. We study potential trends of both subsamples in terms of their chemistry ([O/H], [O/Fe], [O/Mg], and [C/O] versus [Fe/H] and [Mg/H]), age, and position in the Galaxy. Main results are: (a) [O/H] and [O/Fe] ratios versus [Fe/H] show systematic differences between thin and thick disk stars with enhanced O abundance of thick disk stars with respect to thin disk members and a monotonic decrement of [O/Fe] with increasing metallicity, even at metal-rich regime; (b) a smooth correlation of [O/Mg] with age in both populations, suggesting that this abundance ratio can be a good proxy of stellar ages within the Milky Way; (c) Corresponding author: Mariagrazia Franchini Mariagrazia.franchini@inaf.it ∗ Based on observations collected with the FLAMES instrument at VLT/UT2 telescope (Paranal Observatory, ESO, Chile), for the Gaia–ESO Large Public Spectroscopic Survey (188.B–3002, 193.B–0936).

Erratum: Gaia Data Release 2: The kinematics of globular clusters and dwarf galaxies around the Milky Way (Astronomy and Astrophysics (2018) 616 (A12) DOI: 10.1051/0004-6361/201832698)

Abstract: This is a corrigendum to Gaia Collaboration (2018). It corrects errors in Appendix B, which describes the modelling of the Large and Small Magellanic Clouds (LMC and SMC). One of these errors also affects Fig. 18 of the paper, which shows the rotation curve and median radial motion in the LMC. No other results in the paper are affected. There should be no vector products in Appendix B, and everywhere a vector product appears should be a scalar product. This affects Eqs. (B.5), (B.8), (B.10), (B.12), (B.13), and (B.20). Equation (B.10), which defines one component of position within the plane of the galaxy, contains an additional typographical error, and it should have read (Farmula Presented) Equation (B.21) is incorrect. The factor of (ax + by + z) is applied to the wrong part of the equation. It should have read (Farmula Presented) This error affects the derived deprojected motions of stars in the LMC, and means that changes in the observational signature of the bulk motion away from the centre are not properly accounted for. The effect becomes more significant further from the centre. Figure 1 shows the resulting median tangential velocity, vT (the rotation curve), and median radial velocity vR as a function of de-projected radius R for the LMC, which is otherwise produced in the same way as before. The major differences between this and the equivalent figure in Gaia Collaboration (2018) are as follows The rotation curve reaches a greater velocity (~85 km s-1 versus ~75 km s-1) and remains flat beyond 6 kpc, as opposed to starting to fall. The difference in asymmetric drift for the blue and red populations is clearer the blue population, which is typically younger than the redder population, is rotating faster. The apparent outward motion of the stellar populations is much smaller. The blue population has almost no net radial motion, while the red population has one of .8 km s-1 (as opposed to ~20 km s-1). The difference in radial motion between the y 0 populations is dramatically reduced, as is the difference between the value derived assuming the known line-of-sight bulk motion and the one derived leaving this value free.