Context. The second Gaia data release (Gaia DR2) contains high-precision positions, parallaxes, and proper motions for 1.3 billion sources. The resulting Hertzsprung–Russel diagram reveals fine ...structures throughout the mass range. Aims. This paper aims to investigate the content of Gaia DR2 at the low-mass end and to characterize ultra-cool and brown dwarfs. Methods. We first retrieved the sample of spectroscopically confirmed ultra-cool and brown dwarfs in Gaia DR2. We used their locus in the precise Hertzsprung–Russel diagram to select new candidates and to investigate their properties. Results. The number of spectroscopically confirmed objects recovered in Gaia DR2 corresponds to 61% and 74% of the expected number of objects with an estimated Gaia magnitude G est ≤ 21.5 and 20.3, respectively. This fills much of the gap to Gaia DR1. Furthermore, Gaia DR2 contains Ȉ13 000 ≥ M7 and 631 new L candidates. A tentative classification suggests that a few hundred of them are young or subdwarf candidates. Their distance distribution shows that the solar neighborhood census is still incomplete. Conclusions. Gaia DR2 offers a great wealth of information on low-mass objects. It provides a homogeneous and precise catalog of candidates that is worthwhile to be further characterized with spectroscopic observations.
Context.
The nearest stars provide a fundamental constraint for our understanding of stellar physics and the Galaxy. The nearby sample serves as an anchor where all objects can be seen and understood ...with precise data. This work is triggered by the most recent data release of the astrometric space mission
Gaia
and uses its unprecedented high precision parallax measurements to review the census of objects within 10 pc.
Aims.
The first aim of this work was to compile all stars and brown dwarfs within 10 pc observable by
Gaia
and compare it with the
Gaia
Catalogue of Nearby Stars as a quality assurance test. We complement the list to get a full 10 pc census, including bright stars, brown dwarfs, and exoplanets.
Methods.
We started our compilation from a query on all objects with a parallax larger than 100 mas using the Set of Identifications, Measurements, and Bibliography for Astronomical Data database (SIMBAD). We completed the census by adding companions, brown dwarfs with recent parallax measurements not in SIMBAD yet, and vetted exoplanets. The compilation combines astrometry and photometry from the recent
Gaia
Early Data Release 3 with literature magnitudes, spectral types, and line-of-sight velocities.
Results.
We give a description of the astrophysical content of the 10 pc sample. We find a multiplicity frequency of around 27%. Among the stars and brown dwarfs, we estimate that around 61% are M stars and more than half of the M stars are within the range from M3.0 V to M5.0 V. We give an overview of the brown dwarfs and exoplanets that should be detected in the next
Gaia
data releases along with future developments.
Conclusions.
We provide a catalogue of 540 stars, brown dwarfs, and exoplanets in 339 systems, within 10 pc from the Sun. This list is as volume-complete as possible from current knowledge and it provides benchmark stars that can be used, for instance, to define calibration samples and to test the quality of the forthcoming
Gaia
releases. It also has a strong outreach potential.
The Galactic warp revealed by Gaia DR2 kinematics Poggio, E; Drimmel, R; Lattanzi, M G ...
Monthly Notices of the Royal Astronomical Society Letters,
11/2018, Letnik:
481, Številka:
1
Journal Article
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ABSTRACT Using Gaia DR2 astrometry, we map the kinematic signature of the Galactic stellar warp out to a distance of 7 kpc from the Sun. Combining Gaia DR2 and 2-Micron All Sky Survey photometry, we ...identify, via a probabilistic approach, $599 \, 494$ upper main sequence (UMS) stars and $12\, 616\, 068$ giants without the need for individual extinction estimates. The spatial distribution of the UMS stars clearly shows segments of the nearest spiral arms. The large-scale kinematics of both the UMS and giant populations show a clear signature of the warp of the Milky Way, apparent as a gradient of 5–6 km s−1 in the vertical velocities from 8 to 14 kpc in Galactic radius. The presence of the signal in both samples, which have different typical ages, suggests that the warp is a gravitationally induced phenomenon.
Exploring the bulge region of our Galaxy is an interesting but challenging quest because of its complex structure and the highly variable extinction. We re-analyse photometric near-infrared data in ...order to investigate why it is so hard to reach a consensus on the shape and density law of the bulge, as witnessed in the literature. The apparent orientation of the bulge seems to vary with the range of longitude, latitude, and the population considered. To solve the problem we have used the Besançon galaxy model to provide a scheme for parameter fitting of the structural characteristics of the bulge region. The fitting process allows the shape of the bulge’s main structure to be determined. We explore various parameters and shapes for the bulge population, based on Ferrer’s ellipsoids, and fit the shape of the inner disc in the same process. The results show that the main structure has a standard triaxial boxy shape with an orientation of about 13° with respect to the Sun-Galactic centre direction. But the fit is greatly improved when we add a second structure,which is a longer and thicker ellipsoid. We emphasize that our first ellipsoid represents the main boxy bar of the Galaxy and that the thick bulge population could be either (i) a classical bulge slightly flattened by the effect of the bar’s potential; or (ii) an inner thick disc counterpart. With Ferrer’s ellipsoid, the model shows a general agreement with 2MASS data at the level of 10% in the whole bulge region but does not produce the “double clump” feature. However, we show that the double clump seen at intermediate latitudes can be reproduced by adding a slight flare to the bar. To characterize the populations better, we further simulate several fields that have been surveyed in spectroscopy and for which a metallicity distribution function (MDF) are available. The model agrees well with these MDF measured along the minor axis if we assume that the main bar has a mean solar metallicity and the second thicker population has a lower metallicity. It then naturally creates a vertical metallicity gradient by mixing the two populations. In the process of model fitting, we also determine the thin disc parameters. The thin disc is found to have a scale length of 2.2 kpc, in good agreement with previous estimates towards the anticentre, but with a large hole of scale length 1.3 kpc, giving a maximum density in the plane for this population at about 2.3 kpc from the Galactic centre. In the very central part of the bulge on top of our two populations, and by subtracting the fitted ellipsoids, we find evidence of an extra population in the nuclear region, at 2° in longitude and 1° of latitude from the Galactic centre. Its location corresponds well to the central molecular zone, and to the Alard nuclear bar.
Context. Galactic structure studies can be used as a path to constrain the scenario of formation and evolution of our Galaxy. The dependence with the age of stellar population parameters would be ...linked with the history of star formation and dynamical evolution. Aims. We aim to investigate the structures of the outer Galaxy, such as the scale length, disc truncation, warp and flare of the thin disc and study their dependence with age by using 2MASS data and a population synthesis model (the so-called Besançon Galaxy Model). Methods. We have used a genetic algorithm to adjust the parameters on the observed colour–magnitude diagrams at longitudes 80° ≤ ℓ ≤ 280° for | b | ≤ 5.5°. We explored parameter degeneracies and uncertainties. Results. We identify a clear dependence of the thin disc scale length, warp and flare shapes with age. The scale length is found to vary between 3.8 kpc for the youngest to about 2 kpc for the oldest. The warp shows a complex structure, clearly asymmetrical with a node angle changing with age from approximately 165° for old stars to 195° for young stars. The outer disc is also flaring with a scale height that varies by a factor of two between the solar neighbourhood and a Galactocentric distance of 12 kpc. Conclusions. We conclude that the thin disc scale length is in good agreement with the inside-out formation scenario and that the outer disc is not in dynamical equilibrium. The warp deformation with time may provide some clues to its origin.
Context. Future space missions (TESS, CHEOPS, PLATO, and the JWST) will considerably improve our understanding of the formation and history of planetary systems by providing accurate constraints on ...planetary radius, mass, and atmospheric composition. Currently, observations show that the presence of planetary companions is closely linked to the metallicity and the chemical abundances of the host stars. Aims. We aim to build an integrated tool for predicting the planet building blocks (PBBs) composition as a function of the stellar populations to interpret ongoing and future large surveys. The different stellar populations we observe in our Galaxy are characterized by different metallicities and α-element abundances. We here investigate the trends of the expected PBBs composition with the chemical abundance of the host star in different parts of the Galaxy. Methods. We synthesized stellar populations with the Besançon galaxy model, which includes stellar evolutionary tracks that are computed with the stellar evolution code STAREVOL. We integrated a previously published simple stoichiometric model into this code to determine the expected composition of the PBBs. Results. We determine the expected PBB composition around FGK stars for the four galactic populations (thin and thick disks, halo, and bulge) within the Milky Way. Our solar neighborhood simulations are in good agreement with the recent results obtained with the HARPS survey for firon, fw, and the heavy element mass fraction fZ. We present evidence of a clear dependence of firon and fw on the initial alpha abundances α/Fe of the host star. We find that the different initial α/Fe distributions in the different galactic populations lead to a bimodal distribution of PBB composition. Our simulations show an iron valley that separates PBBs with high and low iron mass fractions and a water valley that separates PBBs with high and low water mass fractions. Conclusions. We linked host star abundances and expected PBB composition in an integrated model of the Galaxy. The trends we derive are an important step for statistical analyses of expected planet properties. In particular, internal structure models may use these results to derive statistical trends of rocky planet properties, constrain habitability, and prepare an interpretation of ongoing and future large-scale surveys of exoplanets.
Gaia Early Data Release 3 Fabricius, C.; Luri, X.; Arenou, F. ...
Astronomy and astrophysics (Berlin),
05/2021, Letnik:
649
Journal Article
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Context.
The third
Gaia
data release is published in two stages. The early part,
Gaia
EDR3, gives very precise astrometric and photometric properties for nearly two billion sources together with ...seven million radial velocities from
Gaia
DR2. The full release,
Gaia
DR3, will add radial velocities, spectra, light curves, and astrophysical parameters for a large subset of the sources, as well as orbits for solar system objects.
Aims.
Before the publication of the catalogue, many different data items have undergone dedicated validation processes. The goal of this paper is to describe the validation results in terms of completeness, accuracy, and precision for the
Gaia
EDR3 data and to provide recommendations for the use of the catalogue data.
Methods.
The validation processes include a systematic analysis of the catalogue contents to detect anomalies, either individual errors or statistical properties, using statistical analysis and comparisons to the previous release as well as to external data and to models.
Results.
Gaia
EDR3 represents a major step forward, compared to
Gaia
DR2, in terms of precision, accuracy, and completeness for both astrometry and photometry. We provide recommendations for dealing with issues related to the parallax zero point, negative parallaxes, photometry for faint sources, and the quality indicators.
Gaia Data Release 2 Arenou, F.; Luri, X.; Babusiaux, C. ...
Astronomy and astrophysics (Berlin),
08/2018, Letnik:
616
Journal Article
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Context.
The second
Gaia
data release (DR2) contains very precise astrometric and photometric properties for more than one billion sources, astrophysical parameters for dozens of millions, radial ...velocities for millions, variability information for half a million stars from selected variability classes, and orbits for thousands of solar system objects.
Aims.
Before the catalogue was published, these data have undergone dedicated validation processes. The goal of this paper is to describe the validation results in terms of completeness, accuracy, and precision of the various
Gaia
DR2 data.
Methods.
The validation processes include a systematic analysis of the catalogue content to detect anomalies, either individual errors or statistical properties, using statistical analysis and comparisons to external data or to models.
Results.
Although the astrometric, photometric, and spectroscopic data are of unprecedented quality and quantity, it is shown that the data cannot be used without dedicated attention to the limitations described here, in the catalogue documentation and in accompanying papers. We place special emphasis on the caveats for the statistical use of the data in scientific exploitation. In particular, we discuss the quality filters and the consideration of the properties, systematics, and uncertainties from astrometry to astrophysical parameters, together with the various selection functions.
Context. Despite a rich observational background, few spectroscopic studies have dealt with the measurement of the carbon isotopic ratio in giant stars. However, it is a key element in understanding ...the mixing mechanisms that occur in the interiors of giant stars. Aims. We present the CNO and 12C/13C abundances derived for 71 giant field stars. Then, using this new catalogue and complementary data from the Kepler and Gaia satellites, we study the efficiency of mixing occurring in the giant branch as a function of the stellar properties of the stars (e.g. mass, age, metallicity). Methods. We determined the abundances of CNO and more specifically the carbon isotopic ratio using the high-resolution FIbre-fed Echelle Spectrograph on the Nordic Optical Telescope, for 71 giant field stars. In addition, asteroseismology from the Kepler satellite is available for all stars, providing the stellar masses, ages, and evolutionary states. Finally, astrometry from the Gaia data is also available for most of the sample. We compare these new determinations with stellar evolution models taking into account the effects of transport processes. To exploit the complete potential of our extensive catalogue, and considering both the Milky Way evolution and the impact of stellar evolution, we built mock catalogues using the Besançon Galaxy model in which stellar evolution models taking into account the effects of thermohaline instability are included. Results. We confirm that the carbon isotopic ratio at the surface of core He-burning stars is lower than that of first-ascent RGB stars. The carbon isotopic ratio measured at the surface of the core He-burning stars increases with Fe/H and stellar mass, while it decreases with stellar age. These trends are all nicely explained by the thermohaline mixing that occurs in red giants. We show that our models can explain the behaviour of 12C/13C versus N/O, although the observations seem to show a lower N/O than the models. We also note that more constraints on the thick disc core He-burning stars are needed to understand this difference. Conclusions. Overall, the current model including thermohaline mixing is able to reproduce very well the 12C/13C with the stellar metallicity and with the stellar mass and age.
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