Context. Gaia data and stellar surveys open the way to the construction of detailed 3D maps of the Galactic interstellar (IS) dust based on the synthesis of star distances and extinctions. Dust maps ...are tools of broad use, also for Gaia-related Milky Way studies. Aims. Reliable extinction measurements require very accurate photometric calibrations. We show the first step of an iterative process linking 3D dust maps and photometric calibrations, and improving them simultaneously. Methods. Our previous 3D map of nearby IS dust was used to select low-reddening SDSS/APOGEE-DR14 red giants, and this database served for an empirical effective temperature- and metallicity-dependent photometric calibration in the Gaia G and 2MASS Ks bands. This calibration has been combined with Gaia G-band empirical extinction coefficients recently published, G, J, and Ks photometry and APOGEE atmospheric parameters to derive the extinction of a large fraction of the survey targets. Distances were estimated independently using isochrones and the magnitude-independent extinction KJ−Ks. This new dataset has been merged with the one used for the earlier version of dust map. A new Bayesian inversion of distance-extinction pairs has been performed to produce an updated 3D map. Results. We present several properties of the new map. A comparison with 2D dust emission reveals that all large dust shells seen in emission at middle and high latitudes are closer than 300 pc. The updated distribution constrains the well-debated, X-ray bright North Polar Spur to originate beyond 800 pc. We use the Orion region to illustrate additional details and distant clouds. On the large scale the map reveals a complex structure of the Local Arm. Chains of clouds of 2–3 kpc in length appear in planes tilted by ≃15° with respect to the Galactic plane. A series of cavities oriented along a l ≃ 60–240° axis crosses the Arm. Conclusions. The results illustrate the ongoing synergy between 3D mapping of IS dust and stellar calibrations in the context of Gaia. Dust maps provide prior foregrounds for future calibrations appropriate to different target characteristics or ranges of extinction, allowing us in turn to increase extinction data and produce more detailed and extended maps.
Gaia stellar measurements are currently revolutionizing our knowledge of the evolutionary history of the Milky Way. 3D maps of the interstellar dust provide complementary information and are a tool ...for a wide range of uses. We built 3D maps of the dust in the Local arm and surrounding regions. To do so, Gaia DR2 photometric data were combined with 2MASS measurements to derive extinction toward stars that possess accurate photometry and relative uncertainties on DR2 parallaxes smaller than 20%. We applied a new hierarchical inversion algorithm to the individual extinctions that is adapted to large datasets and to an inhomogeneous target distribution. Each step associates regularized Bayesian inversions in all radial directions and a subsequent inversion in 3D of all their results. Each inverted distribution serves as a prior for the subsequent step, and the spatial resolution is progressively increased. We present the resulting 3D distribution of the dust in a 6 × 6 × 0.8 kpc3 volume around the Sun. Its main features are found to be elongated along different directions that vary from below to above the mid-plane. The outer part of Carina-Sagittarius, mainly located above the mid-plane, the Local arm/Cygnus Rift around and above the mid-plane, and the fragmented Perseus arm are oriented close to the direction of circular motion. The spur of more than 2 kpc length (nicknamed the split) that extends between the Local Arm and Carina-Sagittarius, the compact near side of Carina-Sagittarius, and the Cygnus Rift below the Plane are oriented along l ~40 to 55°. Dust density images in vertical planes reveal a wavy pattern in some regions and show that the solar neighborhood within ~500 pc remains atypical by its extent above and below the Plane. We show several comparisons with the locations of molecular clouds, HII regions, O stars, and masers. The link between the dust concentration and these tracers is markedly different from one region to the other.
Context. The first Gaia data release unlocked the access to photometric information for 1.1 billion sources in the G-band. Yet, given the high level of degeneracy between extinction and spectral ...energy distribution for large passbands such as the Gaia G-band, a correction for the interstellar reddening is needed in order to exploit Gaia data. Aims. The purpose of this manuscript is to provide the empirical estimation of the Gaia G-band extinction coefficient kG for both the red giants and main sequence stars in order to be able to exploit the first data release DR1. Methods. We selected two samples of single stars: one for the red giants and one for the main sequence. Both samples are the result of a cross-match between Gaia DR1 and 2MASS catalogues; they consist of high-quality photometry in the G-, J- and KS-bands. These samples were complemented by temperature and metallicity information retrieved from APOGEE DR13 and LAMOST DR2 surveys, respectively. We implemented a Markov chain Monte Carlo method where we used (G – KS)0 versus Teff and (J – KS)0 versus (G – KS)0, calibration relations to estimate the extinction coefficient kG and we quantify its corresponding confidence interval via bootstrap resampling. We tested our method on samples of red giants and main sequence stars, finding consistent solutions. Results. We present here the determination of the Gaia extinction coefficient through a completely empirical method. Furthermore we provide the scientific community with a formula for measuring the extinction coefficient as a function of stellar effective temperature, the intrinsic colour (G – KS)0, and absorption.
Context. Gaia Data Release 1 allows the recalibration of standard candles such as the red clump stars. To use those stars, they first need to be accurately characterised. In particular, colours are ...needed to derive interstellar extinction. As no filter is available for the first Gaia data release and to avoid the atmosphere model mismatch, an empirical calibration is unavoidable. Aims. The purpose of this work is to provide the first complete and robust photometric empirical calibration of the Gaia red clump stars of the solar neighbourhood through colour–colour, effective temperature–colour, and absolute magnitude–colour relations from the Gaia, Johnson, 2MASS, Hipparcos, Tycho-2, APASS-SLOAN, and WISE photometric systems, and the APOGEE DR13 spectroscopic temperatures. Methods. We used a 3D extinction map to select low reddening red giants. To calibrate the colour–colour and the effective temperature–colour relations, we developed a MCMC method that accounts for all variable uncertainties and selects the best model for each photometric relation. We estimated the red clump absolute magnitude through the mode of a kernel-based distribution function. Results. We provide 20 colour versus G−Ks relations and the first Teff versus G−Ks calibration. We obtained the red clump absolute magnitudes for 15 photometric bands with, in particular, MKs = (−1.606 ± 0.009) and MG = (0.495 ± 0.009) + (1.121 ± 0.128)(G−Ks−2.1). We present a dereddened Gaia-TGAS HR diagram and use the calibrations to compare its red clump and its red giant branch bump with Padova isochrones.
Context.
The recent third data release (DR3) of
Gaia
has brought some new exciting data about stellar binaries. It provides new opportunities to fully characterize more stellar systems and ...contributes to enriching our global knowledge of stellar behaviour.
Aims.
By combining the new
Gaia
non-single stars catalogue with double-lined spectroscopic binaries (SB2), we can determine the individual masses and luminosities of the components. To fit an empirical mass-luminosity relation in the
Gaia
G
band, lower-mass stars must be added. These masses can be derived using
Gaia
-resolved wide binaries combined with literature data.
Methods.
Using the BINARYS tool, we combined the astrometric non-single star solutions in the
Gaia
DR3 with SB2 data from two other catalogues: the 9th Catalogue of Spectroscopic Binary orbits (SB9), and APOGEE. We also searched for low-mass stars that are resolved in
Gaia
with direct imaging and H
IPPARCOS
data or with a literature mass fraction.
Results.
The combination of
Gaia
astrometric non-single star solutions with double-lined spectroscopic data enabled us to characterize 43 binary systems with SB9 and 13 systems with APOGEE. We furthermore derived the masses of 6 low-mass binaries that are resolved with
Gaia
. We then derived an empirical mass-luminosity relation in the
Gaia
G
band down to 0.12 ℳ
⊙
.
Aims. We seek to constrain the formation of the Galactic bulge by analysing the detailed chemical composition of a large sample of red clump stars in Baade’s window. These stars were selected to ...minimise the contamination by other Galactic components, so they are good tracers of the bulge metallicity distribution in Baade’s window, at least for stars more metal-rich than ~−1.5. Methods. We used an automatic procedure to measure Fe/H differentially with respect to the metal-rich star μLeo in a sample of 219 bulge red clump stars from R = 20 000 resolution spectra obtained with FLAMES/GIRAFFE at the VLT. For a subsample of 162 stars, we also derived Mg/H from spectral synthesis around the Mg i triplet at λ 6319 Å. Results. The Fe and Mg metallicity distributions are both asymmetric with median values of +0.16 and +0.21, respectively. They show only a small proportion of stars at low metallicities, extending down to Fe/H = −1.1 or Mg/H = −0.7. The iron distribution is clearly bimodal, as revealed both by a deconvolution (from observational errors) and a Gaussian decomposition. The decomposition of the observed Fe and Mg metallicity distributions into Gaussian components yields two populations of equal sizes (50% each): a metal-poor component centred on Fe/H = −0.30 and Mg/H = −0.06 with a large dispersion and a narrow metal-rich component centred on Fe/H = +0.32 and Mg/H = +0.35. The metal-poor component shows high Mg/Fe ratios (around 0.3), while stars in the metal-rich component are found to have nearly solar ratios. Kinematical differences between the two components have also been found: the metal-poor component shows kinematics compatible with an old spheroid, while the metal-rich component is consistent with a population supporting a bar. In view of their chemical and kinematical properties, we suggest different formation scenarii for the two populations: a rapid formation time scale as an old spheroid for the metal-poor component (old bulge) and for the metal-rich component, a formation on a longer time scale driven by the evolution of the bar (pseudo-bulge). The observations are described well by a simple model consisting of two components: a simple closed box model to predict the metal-poor population contribution and a local thin disc metallicity distribution, shifted in metallicity, to represent the metal-rich population. The pseudo-bulge is compatible with its being formed from the inner thin disc, assuming high (but plausible) values of the gradients in the early Galactic disc.
Abstract
In preparation for the release of the astrometric orbits of Gaia, Shahaf et al. (2019) proposed a triage technique to identify astrometric binaries with compact companions based on their ...astrometric semimajor axis, parallax, and primary mass. The technique requires the knowledge of the appropriate mass–luminosity relation to rule out single or close-binary main-sequence companions. The recent publication of the Gaia DR3 astrometric orbits used a schematic version of this approach, identifying 735 astrometric binaries that might have compact companions. In this communication, we return to the triage of the DR3 astrometric binaries with more careful analysis, estimating the probability for its astrometric secondary to be a compact object or a main-sequence close binary. We compile a sample of 177 systems with highly probable non-luminous massive companions, which is smaller but cleaner than the sample reported in Gaia DR3. The new sample includes eight candidates to be black-hole systems with compact-object masses larger than 2.4 M⊙. The orbital–eccentricity–secondary–mass diagram of the other 169 systems suggests a tentative separation between the white-dwarf and the neutron-star binaries. Most white-dwarf binaries are characterized by small eccentricities of about 0.1 and masses of 0.6 M⊙, while the neutron star binaries display typical eccentricities of 0.4 and masses of 1.3 M⊙.
Context. Constraints on the Galactic bulge and bar structures and on their formation history from stellar kinematics and metallicities mainly come from relatively high-latitude fields (|b| > 4°) ...where a complex mix of stellar population is seen. Aims. We aim here to constrain the formation history of the Galactic bar by studying the radial velocity and metallicity distributions of stars in situ (|b| ≤ 1°). Methods. We observed red clump stars in four fields along the bar’s major axis (l = 10°, −6°, 6° and b = 0° plus a field at l = 0°, b = 1°) with low-resolution spectroscopy from FLAMES/GIRAFFE at the VLT, observing around the Ca ii triplet. We developed robust methods for extracting radial velocity and metallicity estimates from these low signal-to-noise spectra. We derived distance probability distributions using Bayesian methods rigorously handling the extinction law. Results. We present radial velocities and metallicity distributions, as well as radial velocity trends with distance. We observe an increase in the radial velocity dispersion near the Galactic plane. We detect the streaming motion of the stars induced by the bar in fields at l = ±6°, the highest velocity components of this bar stream being metal-rich (Fe/H ~ 0.2 dex). Our data is consistent with a bar that is inclined at 26 ± 3° from the Sun-Galactic centre line. We observe a significant fraction of metal-poor stars, in particular in the field at l = 0°, b = 1°. We confirm the flattening of the metallicity gradient along the minor axis when getting closer to the plane, with a hint that it could actually be inverted. Conclusions. Our stellar kinematics corresponds to the expected behaviour of a bar issued from the secular evolution of the Galactic disc. The mix of several populations, seen further away from the plane, is also seen in the bar in situ since our metallicity distributions highlight a different spatial distribution between metal-poor and metal-rich stars, the more metal-poor stars being more centrally concentrated.
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 campaigns 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.
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