We construct from Gaia eDR3 an extensive catalog of spatially resolved binary stars within $\approx$ 1 kpc of the Sun, with projected separations ranging from a few au to 1 pc. We estimate the probability that each pair is a chance alignment empirically, using the Gaia catalog itself to calculate the rate of chance alignments as a function of observables. The catalog contains 1.3 (1.1) million binaries with >90% (>99%) probability of being bound, including 16,000 white dwarf -- main sequence (WD+MS) binaries and 1,400 WD+WD binaries. We make the full catalog publicly available, as well as the queries and code to produce it. We then use this sample to calibrate the published Gaia DR3 parallax uncertainties, making use of the binary components' near-identical parallaxes. We show that these uncertainties are generally reliable for faint stars ($G\gtrsim 18$), but are underestimated significantly for brighter stars. The underestimates are generally $\le 30\%$ for isolated sources with well-behaved astrometry, but are larger (up to 80%) for apparently well-behaved sources with a companion within $\lesssim 4$ arcsec, and much larger for sources with poor astrometric fits. We provide an empirical fitting function to inflate published $σ_{\varpi}$ values for isolated sources. The public catalog offers wide ranging follow-up opportunities: from calibrating spectroscopic surveys, to precisely constraining ages of field stars, to the masses and the initial-final mass relation of white dwarfs, to dynamically probing the Galactic tidal field.
Using parallaxes from Gaia DR2, we estimate the distance to the globular clusters 47 Tuc and NGC 362, taking advantage of the background stars in the Small Magellanic Cloud and quasars to account for various parallax systematics. We found the parallax to be dependent on the Gaia DR2 G apparent magnitude for stars with $13<\textrm{G}<18$ , where brighter stars have a lower parallax zero point than fainter stars. The distance to 47 Tuc was found to be $4.45\pm0.01\pm0.12$ kpc, and for NGC 362 $8.54\pm0.20\pm0.44$ kpc with random and systematic errors listed respectively. This is the first time a…
The Gaia Early Data Release 3 (EDR3) provides trigonometric parallaxes for 1.5 billion stars, with reduced systematics compared to Gaia Data Release 2 and reported precisions better by up to a factor of two. New to EDR3 is a tentative model for correcting the parallaxes of magnitude-, position-, and color-dependent systematics for five- and six-parameter astrometric solutions, $Z_5$ and $Z_6$. Using a sample of over 2,000 first-ascent red giant branch stars with asteroseismic parallaxes, I perform an independent check of the $Z_5$ model in a Gaia magnitude range of $9 \lesssim G \lesssim 13$ a…
Like Hipparcos, Gaia is designed to give absolute parallaxes, independent of any astrophysical reference system. And indeed, Gaia's internal zero-point error for parallaxes is likely to be smaller than any individual parallax error. Nevertheless, due in part to mechanical issues of unknown origin, there are many astrophysical questions for which the parallax zero-point error $σ(π_0)$ will be the fundamentally limiting constraint. These include the distance to the Large Magellanic Cloud and the Galactic Center. We show that by using the photometric parallax estimates for RR Lyrae stars (RRL) wi…
We independently determine the zero-point offset of the Gaia early Data Release-3 (EDR3) parallaxes based on $\sim 110,000$ W Ursae Majoris (EW)-type eclipsing binary systems. EWs cover almost the entire sky and are characterized by a relatively complete coverage in magnitude and color. They are an excellent proxy for Galactic main-sequence stars. We derive a $W1$-band Period-Luminosity relation with a distance accuracy of $7.4\%$, which we use to anchor the Gaia parallax zero-point. The final, global parallax offsets are $-28.6\pm0.6$ $μ$as and $-25.4\pm4.0$ $μ$as (before correction) and $4.2…
We used the "primary dataset" of Gaia Data Release 1 (DR1) to search for parallax measurements of central stars (CSs) of Galactic planetary nebulae (PNe), to determine PN distances. We found that a trigonometric parallax is available for 16 CSs, seven of which with relative uncertainty below 80%. The limited comparison of these trigonometric distances to other reliable individual determinations discloses good correlation between the two sets, with the Gaia parallax distances being lower by a factor of ~0.1 dex in the logarithmic distances. We tested with the Gaia parallaxes the most popular Ga…
Classical Cepheids (DCEPs) are the most important standard candles in the extra-galactic distance scale thanks to the Period-Luminosity ($\rm PL$), Period-Luminosity-Color ($\rm PLC$) and Period-Wesenheit ($\rm PW$) relations that hold for these objects. The advent of the {\it Gaia} mission, and in particular the Early Data Release 3 (EDR3) provided accurate parallaxes to calibrate these relations. In order to fully exploit {\it Gaia} measurements, the zero point (ZP) of {\it Gaia} parallaxes should be determined with an accuracy of a few $\rm μas$. The individual ZP corrections provided by th…
We compare the parallaxes of stars from VLBI astrometry in the literature to those in the Gaia DR2 catalog. Our full sample contains young stellar objects, evolved AGB stars, pulsars and other radio stars. Excluding AGB stars, which show significant discrepancies between Gaia and VLBI parallaxes, and stars in binary systems, we obtain an average, systematic, parallax offset of $-75 \pm 29~μ$as for Gaia DR2, consistent with their estimate of a parallax zero-point between $-100$ and 0 $μ$as.
Using {\it Gaia} Early Data Release 3 (EDR3) parallaxes and Bayesian inference, we infer a parallax of the Westerlund 1 (Wd1) cluster. We find a parallax of $0.34\pm{0.05}$ mas corresponding to a distance of $2.8^{+0.7}_{-0.6}$ kpc. The new {\it Gaia} EDR3 distance is consistent with our previous result using {\it Gaia} DR2 parallaxes. This confirms that Wd1 is less massive and older than previously assumed. Compared to DR2, the EDR3 individual parallax uncertainties for each star decreased by 30\%. However, the aggregate parallax uncertainty for the cluster remained the same. This suggests th…
The systematic offset of Gaia parallaxes has been widely reported with Gaia's second data release, and it is expected to persist in future Gaia data. In order to use Gaia parallaxes to infer distances to high precision, we develop a hierarchical probabilistic model to determine the Gaia parallax zero point offset along with the calibration of an empirical model for luminosity of red clump stars by combining astrometric and photometric measurements. Using a cross-matched sample of red clump stars from the Apache Point Observatory Galactic Evolution Experiment (APOGEE) and Gaia Data Release 2 (D…
Precise measurement of the fundamental parameters of stellar systems, including mass and radius, depends critically on how well the stellar distances are known. Astrometry from space provides parallax measurements of unprecented accuracy, from which distances can be derived, initially from the Hipparcos mission, with further refinement of that analysis provided by van Leeuwen in 2007. The publication of the Gaia DR2 catalogue promises a dramatic improvement in the available data. We have recalculated the dynamical masses of a sample of 1 700 close visual binary stars using Gaia DR2 and compare…
We present an independent examination of the parallax zero-point of the Third Gaia Early Data Release (hereafter EDR3), using the LAMOST primary red clump (PRC) stellar sample. A median parallax offset of around $26 μ$as, slightly larger than that found by examination of distant quasars, is found for both the five- and six-parameter solutions in EDR3, based on samples of over 63,000 and 2000 PRC stars, respectively. Similar to the previous investigation of Lindegren et al., to which we compare our results, the parallax zero-point exhibits clear dependencies on the $G$ magnitudes, colors, and p…
3350 objects from the Sixth catalog of orbits of visual binary stars (ORB6) are investigated to validate Gaia EDR3 parallaxes and provide mass estimates for the systems. We show that 2/3 of binaries with 0.2 - 0.5 arcsec separation are left without a parallax solution in EDR3. A special attention is paid to 521 pairs with parallax known separately for both components. We find 16 entries that are deemed to be chance alignments of unrelated stars. At once we show examples of high-confidence binary systems with significant differences in the reported parallaxes of their components. Next we conclu…
The second data release of \it Gaia \rm revealed a parallax zero point offset of $-0.029$~mas based on quasars. The value depended on the position on the sky, and also likely on magnitude and colour. The offset and its dependence on other parameters inhibited an improvement in the local distance scale using e.g. the Cepheid and RR Lyrae period-luminosity relations. Analysis of the recent \it Gaia \rm Early Data Release 3 (EDR3) reveals a mean parallax zero point offset of $-0.021$~mas based on quasars. The \it Gaia \rm team addresses the parallax zero point offset in detail and proposes a reci…
We present new luminosity-metallicity (LZ; MV-[Fe/H] and MG-[Fe/H]) relations and, for the first time, empirical, Gaia three-band (G,GBP,GRP) period-Wesenheit-metallicity (PWZ) relations of RR Lyrae stars (RRLs) derived using a hierarchical Bayesian approach and new accurate parallaxes published for these variables in the Gaia Early Data Release 3 (EDR3). In a previous study we obtained Bayesian hierarchically-derived LZ relations from a sample of about four hundred Milky Way field RRLs with G-band light curves and trigonometric parallaxes published in the Gaia Data Release 2 (DR2), using V me…
Recent results have suggested that there is tension between the Gaia DR1 TGAS distances and the distances obtained using luminosities determined by eclipsing binaries or asteroseismology on red giant stars. We use the $K_s$-band luminosities of red clump stars, identified and characterized by asteroseismology, to make independent distance estimates. Our results suggest that Gaia TGAS distances contain a systematic error that decreases with increasing distance. We propose a correction to mitigate this offset as a function of parallax that is valid for the Kepler field and values of parallax tha…
We have studied the zero-point offset of Gaia early Data Release 3 (EDR3) parallaxes based on a sample of 0.3 million giant stars built from the LAMOST data with distance accuracy better than 8.5\%. The official parallax zero-point corrections largely reduce the global offset in the Gaia EDR3 parallaxes: the global parallax offsets are $-$27.9 $μ$as and $-$26.5 $μ$as (before correction) and $+$2.6 $μ$as and $+$2.9 $μ$as (after correction) for the five- and six-parameter solutions, respectively. The bias of the raw parallax measurements is significantly dependent on the $G$ magnitudes, spectral…
Stellar distances constitute a foundational pillar of astrophysics. The publication of 1.47 billion stellar parallaxes from Gaia is a major contribution to this. Yet despite Gaia's precision, the majority of these stars are so distant or faint that their fractional parallax uncertainties are large, thereby precluding a simple inversion of parallax to provide a distance. Here we take a probabilistic approach to estimating stellar distances that uses a prior constructed from a three-dimensional model of our Galaxy. This model includes interstellar extinction and Gaia's variable magnitude limit. …
Context. Currently galactic exploration is being revolutionized by a flow of new data: Gaia provides measurements of stellar distances and kinematics; growing numbers of spectroscopic surveys provide values of stellar atmospheric parameters and abundances of elements; and Kepler and K2 missions provide asteroseismic information for an increasing number of stars. Aims. In this work we aim to determine stellar distances and ages using Gaia and spectrophotometric data in a consistent way. We estimate precisions of age and distance determinations with Gaia end-of-mission and TGAS parallax precisio…
We matched the astrometry of central stars (CSs) of spectroscopically-confirmed Galactic planetary nebulae (PNe) with DR2 Gaia parallaxes ($p$), finding 430 targets in common with $p>0$ and $|σ_{\rm p}/p|<1$. A catalog of PNe whose CSs have DR2 Gaia parallaxes is presented in Table 1. We compared DR2 parallaxes with those in the literature, finding a good correlation between the two samples. We used PNe parallaxes to calibrate the Galactic PN distance scale. Restricting the sample to objects with 20$\%$ parallax accuracy, we derive the distance scale ${\rm log}(R_{\rm pc})=-(0.226\pm0.0155)\ti…
Westerlund 1 (Wd1) is potentially the largest star cluster in the Galaxy. That designation critically depends upon the distance to the cluster, yet the cluster is highly obscured, making luminosity-based distance estimates difficult. Using {\it Gaia} Data Release 2 (DR2) parallaxes and Bayesian inference, we infer a parallax of $0.35^{+0.07}_{-0.06}$ mas corresponding to a distance of $2.6^{+0.6}_{-0.4}$ kpc. To leverage the combined statistics of all stars in the direction of Wd1, we derive the Bayesian model for a cluster of stars hidden among Galactic field stars; this model includes the pa…
We use 612 single stars with previously published trigonometric parallaxes placing them within 25 pc to evaluate parallaxes released in Gaia's first data release (DR1). We find that the Gaia parallaxes are, on average, $0.24 \pm 0.02$ mas smaller than the weighted mean trigonometric parallax values for these stars in the solar neighborhood. We also find that the offset changes with distance out to 100 pc, in the sense that the closer the star, the larger the offset. We find no systematic trends in the parallax offsets with stellar $V$ magnitude, $V-K$ color, or proper motion. We do find that t…
We derive Bayesian distances for all stars in the RV sample of Gaia DR2, and use the statistical method of Schoenrich, Binney & Asplund(2012) to validate the distances and test the Gaia parallaxes. In contrast to other methods, which rely on special sources, our method directly tests the distances to all stars in our sample. We find clear evidence for a near-linear trend of distance bias f with distance s, proving a parallax offset delta p. On average, we find delta p = -0.054 mas (parallaxes in Gaia DR2 need to be increased) when accounting for the parallax uncertainty under-estimate in the G…
New catalog of distances to planetary nebulae based on Gaia parallaxes and statistical distances
Instituto de Astronomía, Universidad Nacional Autónoma de México（墨西哥国立自治大学天文学研究所）；Instituto Nacional de Astrofísica, Óptica y Electrónica（国家天体物理学、光学和电子学研究所）
As primary anchors of the distance scale, Cepheid stars play a crucial role in our understanding of the distance scale of the Universe because of their period-luminosity relation. Determining precise and consistent parameters (radius, temperature, color excess, and projection factor) of Cepheid pulsating stars is therefore very important. With the high-precision parallaxes delivered by the early third Gaia data release, we aim to derive various parameters of Cepheid stars in order to calibrate the period-luminosity and period-radius relations and to investigate the relation of period to p-fact…
Investigating Gaia EDR3 parallax systematics using asteroseismology of Cool Giant Stars observed by Kepler, K2, and TESS II. Deciphering Gaia parallax systematics using red clump stars
Classical Cepheids provide the foundation for the empirical extragalactic distance ladder. Milky Way Cepheids are the only stars in this class accessible to trigonometric parallax measurements. However, the parallaxes of Cepheids from the second Gaia data release (GDR2) are affected by systematics because of the absence of chromaticity correction, and occasionally by saturation. As a proxy for the parallaxes of 36 Galactic Cepheids, we adopt either the GDR2 parallaxes of their spatially resolved companions or the GDR2 parallax of their host open cluster. This novel approach allows us to bypass…
CONTEXT. Gaia EDR3 has produced parallaxes for 1.468x10^9 sources but there are calibration issues that require corrections to the published values and uncertainties. AIMS. We want to characterize the behavior of the uncertainties of the Gaia EDR3 parallaxes. We also aim to provide a procedure for the calculation of distances to stars and stellar clusters. METHODS. We reanalyze some of the data in the calibration papers for QSO and LMC parallaxes and combine those results with measurements for six bright GCs. We calculate the angular covariance of EDR3 parallaxes at small separations based on …
The global survey of star clusters in the Milky Way (MWSC) is a comprehensive list of 3061 objects that provides, among other parameters, distances to clusters based on isochrone fitting. The Tycho-Gaia Astrometric Solution (TGAS) catalogue, which is a part of Gaia data release 1 (Gaia DR1), delivers accurate trigonometric parallax measurements for more than 2 million stars, including those in star clusters. We compare the open cluster photometric distance scale with the measurements given by the trigonometric parallaxes from TGAS to evaluate the consistency between these values. The average p…
We present an independent confirmation of the zero-point offset of ${\rm \it Gaia}$ Data Release 2 (DR2) parallaxes using asteroseismic data of evolved stars in the ${\rm \it Kepler}$ field. Using well-characterized red giant branch (RGB) stars from the APOKASC-2 catalogue we identify a ${\rm \it Gaia}$ astrometric pseudo-color ($ν_{\rm eff}$)- and ${\rm \it Gaia}$ $G$-band magnitude-dependent zero-point offset of $\varpi_{\rm seis} - \varpi_{Gaia} = 52.8 \pm 2.4 {\rm\ (rand.)} \pm 8.6 {\rm\ (syst.)} - (150.7 \pm 22.7)(ν_{\rm eff} - 1.5) - (4.21 \pm 0.77)(G - 12.2) μ{\rm as}$, in the sense tha…
We present results from the analysis of 401 RR Lyrae stars (RRLs) belonging to the field of the Milky Way (MW). For a fraction of them multi-band ($V$, $K_{\rm s}$, $W1$) photometry, metal abundances, extinction values and pulsation periods are available in the literature and accurate trigonometric parallaxes measured by the Gaia mission alongside Gaia $G$-band time-series photometry have become available with the Gaia second data release (DR2) on 2018 April 25. Using a Bayesian fitting approach we derive new near-, mid-infrared period-absolute magnitude-metallicity ($PMZ$) relations and new a…
Estimating the distances to asymptotic giant branch (AGB) stars using optical measurements of their parallaxes is not straightforward because of the large uncertainties introduced by their dusty envelopes, their large angular sizes, and their surface brightness variability. We compared the parallaxes from Gaia DR3 with parallaxes measured with maser observations with very long baseline interferometry (VLBI) to determine a statistical correction factor for the DR3 parallaxes using a sub-sample of 33 maser-emitting oxygen-rich nearby AGB stars. We found that the nominal errors on the Gaia DR3 pa…
Previous analyses of various standard candles observed by the Gaia satellite have reported statistically significant systematics in the parallaxes that have improved from $\sim$250 $μ$as in the first data release (DR1) to 50--80 $μ$as in the second data release (DR2). Here we examine the parallaxes newly reported in the Gaia early third data release (EDR3) using the same sample of benchmark eclipsing binaries (EBs) we used to assess the DR1 and DR2 parallaxes. We find a mean offset of $-37\pm20$ $μ$as (Gaia$-$EB), which decreases to $-15\pm18$ $μ$as after applying the corrections recommended b…
Pulsating stars, such as Cepheids, Miras, and RR Lyrae stars, are important distance indicators and calibrators of the "cosmic distance ladder", and yet their period-luminosity-metallicity (PLZ) relations are still constrained using simple statistical methods that cannot take full advantage of available data. To enable optimal usage of data provided by the Gaia mission, we present a probabilistic approach that simultaneously constrains parameters of PLZ relations and uncertainties in Gaia parallax measurements. We demonstrate this approach by constraining PLZ relations of type $ab$ RR Lyrae st…
(abridged)Multiple systems for which the astrometric and spectroscopic orbit are known offer the unique possibility of determining the distance to these systems directly without any assumptions. They are therefore ideal objects for a comparison of Gaia data release 3 (GDR3) parallax data, especially since GDR3 presents the results of the non-single star (NSS) analysis that potentially results in improved parallaxes. An sample of 192 orbital parallax determinations for 186 systems is compiled from the literature. The stars are also potentially in wide binary systems, and 37 candidates were foun…
Relativistic models of light propagation adopted for high-precision astrometry are based on the parametrised post-Newtonian formalism, which provides a framework for examining the effects of a hypothetical violation of general relativity on astrometric data. Astrometric observations are strongly affected by the post-Newtonian parameter $γ$ describing the strength of gravitational light deflection. We study both analytically and numerically how a deviation in the PPN parameter $γ$ from unity, which is the value predicted by general relativity, affects the parallax estimations in Gaia-like astro…
Featuring greatly improved astrometry and precise radial velocities (RVs), the second data release (DR2) from Gaia affords us a unique opportunity to test the validity of samples of stellar wide binaries. In a previous work, we presented a set of wide binaries identified in the joint Tycho-Gaia Astrometric Solution catalog. Here, we use DR2 to confirm the low contamination rate of this sample, thereby verifying the effectiveness of our algorithm for application to DR2 data.
Convection plays an essential role in the emerging intensity for many stars that will be observed by Gaia. Convective-related surface structures affect the shape, shift, and asymmetry of absorption lines, the phocentric and photometric variability causing bias in Gaia measurements. Regarding the importance of Gaia mission and its goals, it is mandatory to have the best models of the observed stars. 3D time-dependent hydrodynamical simulations of surface convection are crucial to model the photosphere of late type stars in a very realistic way. These simulations are an important tool to correct…
Westerlund 1 (Wd 1) is one of the most massive young star clusters in the Milky Way. Although relevant for star formation and evolution, its fundamental parameters are not yet very well constrained. We aim to derive an accurate distance and provide constraints on the cluster age. We used the photometric and astrometric information available in the Gaia Early Data Release 3 (Gaia-EDR3) to infer its distance of 4.06$^{+0.36}_{-0.34}$ kpc. Modelling of the eclipsing binary system W36, reported in Paper II, led to the distance of 4.03$\pm$0.25 kpc, in agreement with the Gaia-EDR3 distance and, the…
Context. The first release of astrometric data from Gaia will contain the mean stellar positions and magnitudes from the first year of observations, and proper motions from the combination of Gaia data with Hipparcos prior information (HTPM). Aims. We study the potential of using the positions from the Tycho-2 Catalogue as additional information for a joint solution with early Gaia data. We call this the Tycho-Gaia astrometric solution (TGAS). Methods. We adapt Gaia's Astrometric Global Iterative Solution (AGIS) to incorporate Tycho information, and use simulated Gaia observations to demonstra…
With contemporary infrared spectroscopic surveys like APOGEE, red-giant stars can be observed to distances and extinctions at which Gaia parallaxes are not highly informative. Yet the combination of effective temperature, surface gravity, composition, and age - all accessible through spectroscopy - determines a giant's luminosity. Therefore spectroscopy plus photometry should enable precise spectrophotometric distance estimates. Here we use the APOGEE-Gaia-2MASS-WISE overlap to train a data-driven model to predict parallaxes for red-giant branch stars with $0<\log g\leq2.2$ (more luminous than…
The importance of studying the Gaia DR2 parallax zero-point by external means was underlined by Lindegren et al. (2018), 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, a…
For application to surveys of interstellar matter and Galactic structure, we compute new spectrophotometric distances to 139 OB stars frequently used as background targets for UV spectroscopy. Many of these stars have updated spectral types and digital photometry with reddening corrections from the Galactic O-Star (GOS) spectroscopic survey. We compare our new photometric distances to values used in previous IUE and FUSE surveys and to parallax distances derived from Gaia-DR2, after applying a standard (0.03 mas) offset from the quasar celestial reference frame. We find substantial differences…
Context. The Gaia satellite will measure highly accurate absolute parallaxes of hundreds of millions of stars by comparing the parallactic displacements in the two fields of view of the optical instrument. The requirements on the stability of the 'basic angle' between the two fields are correspondingly strict, and possible variations (on the microarcsec level) are therefore monitored by an on-board metrology system. Nevertheless, since even very small periodic variations of the basic angle might cause a global offset of the measured parallaxes, it is important to find independent verification …
We present evidence for a spatially-dependent systematic error in the first data release of ${\it Gaia}$ parallaxes based on comparisons to asteroseismic parallaxes in the ${\it Kepler}$ field, and present a parametrized model of the angular dependence of these systematics. We report an error of $0.059^{+0.004}_{-0.004}$mas on scales of 0.3deg, which decreases for larger scales to become $0.011^{+0.006}_{-0.004}$mas at 8deg. This is consistent with the $\sim2\%$ zeropoint offset for the whole sample discussed by Huber et al., and is compatible with the effect predicted by the ${\it Gaia}$ team…
On the basis of an extended set of nonlinear convective RR Lyrae pulsation models we derive the first theoretical light curves in the Gaia bands and the corresponding intensity-weighted mean magnitudes and pulsation amplitudes. The effects of chemical com-position on the derived Bailey diagrams in the Gaia filters are discussed for both Fundamental and First Overtone mode pulsators. The inferred mean magnitudes and colors are used to derive the first theoretical Period-Wesenheit relations for RR Lyrae in the Gaia filters. The application of the theoretical Period-Wesenheit relations for both t…
We investigate the nature of nearby (10-15 kpc) high-speed stars in the Gaia DR2 archive identified on the basis of parallax, proper motion and radial velocity. Together with a consideration of their kinematic, orbital, and photometric properties, we develop a novel strategy for evaluating whether high speed stars are statistical outliers of the bound population or unbound stars capable of escaping the Galaxy. Out of roughly 1.5 million stars with radial velocities, proper motions, and 5-sigma parallaxes, we identify just over 100 high-speed stars. Of these, only two have a nearly 100% chance …
For the vast majority of stars in the second Gaia data release, reliable distances cannot be obtained by inverting the parallax. A correct inference procedure must instead be used to account for the nonlinearity of the transformation and the asymmetry of the resulting probability distribution. Here we infer distances to essentially all 1.33 billion stars with parallaxes published in the second \gaia\ data release. This is done using a weak distance prior that varies smoothly as a function of Galactic longitude and latitude according to a Galaxy model. The irreducible uncertainty in the distanc…
CONTEXT. The Gaia EDR3 parallaxes constitute the most detailed and accurate dataset that can be currently used to determine stellar distances in the solar neighborhood. Nevertheless, there is still room for improvement in their calibration and systematic effects can be further reduced in some circumstances. AIMS. The aim of this paper is to determine an improved Gaia EDR3 parallax bias as a function of magnitude, color, and ecliptic latitude using a single method applied to stars in open clusters, globular clusters, the LMC, and the SMC. METHODS. I study the behavior of the residuals or differ…
The present work aims to build a new statistical distance scale for planetary nebulae (PNe) based on a rigorous calibration sample. The distances of the calibration sample are derived from the trigonometric parallax method using the recent measurements of Gaia early third data release (Gaia EDR3). The new distance scale is created by applying the well-known linear relationship between the radio surface brightness temperature and the nebular radius. The calibration sample is made up of 96 PNe of accurately computed distances with uncertainties less than $20\%$. Earlier ground- and space-based t…
The Bajamar Star is an early O star that ionizes the North America/Pelican Nebulae. In projection, it is near the geometric center of the H II region, but appears to lie outside any of the main stellar subgroups. Furthermore, in Gaia DR2, there were slight discrepancies between this star and the rest of the system in parallax (2$σ$ larger) and relative tangential velocity (~6 km/s). Using Gaia EDR3, we find that the parallax discrepancy has disappeared, but the velocity difference remains. These results are consistent with the star having escaped from a subgroup.
Using a sample of 81 galactic, detached eclipsing binary stars we investigated the global zero-point shift of their parallaxes with the Gaia Data Release 2 (DR2) parallaxes. The stars in the sample lay in a distance range of 0.04-2 kpc from the Sun. The photometric parallaxes π_Phot of the eclipsing binaries were determined by applying a number of empirical surface brightness - color (SBC) relations calibrated on optical-infrared colors. For each SBC relation we calculated the individual differences dπ_i = (π_Gaia - π_Phot)_i and then we calculated unweighted and weighted means. As the sample …
We present MINESweeper, a tool to measure stellar parameters by jointly fitting observed spectra and broadband photometry to model isochrones and spectral libraries. This approach enables the measurement of spectrophotometric distances, in addition to stellar parameters such as Teff, log(g), [Fe/H], [a/Fe], and radial velocity. MINESweeper employs a Bayesian framework and can easily incorporate a variety of priors, including Gaia parallaxes. Mock data are fit in order to demonstrate how the precision of derived parameters depends on evolutionary phase and SNR. We then fit a selection of data i…
Several large stellar spectroscopic surveys are producing overwhelming amounts of data that can be used for determining stellar atmospheric parameters and chemical abundances. Nonetheless, the accuracy achieved in the derived astrophysical parameters is still insufficient, mainly because of the paucity of adequate calibrators, particularly in the metal-poor regime ([Fe/H] $\leq -$1.0). Here, we introduce the Titans metal-poor reference stars: a sample of 41 dwarf and subgiant stars with accurate parameters. Effective temperatures (Teff) were derived by fitting observed H$α$ profiles with synth…
We present a comparison of parallaxes and radii from asteroseismology and Gaia DR1 (TGAS) for 2200 Kepler stars spanning from the main sequence to the red giant branch. We show that previously identified offsets between TGAS parallaxes and distances derived from asteroseismology and eclipsing binaries have likely been overestimated for parallaxes <~ 5-10 mas (~ 90-98% of the TGAS sample). The observed differences in our sample can furthermore be partially compensated by adopting a hotter Teff scale (such as the infrared flux method) instead of spectroscopic temperatures for dwarfs and subgiant…
We apply the twin method to determine parallaxes to 232,545 stars of the RAVE survey using the parallaxes of Gaia DR1 as a reference. To search for twins in this large dataset, we apply the t-stochastic neighbour embedding t-SNE projection which distributes the data according to their spectral morphology on a two dimensional map. From this map we choose the twin candidates for which we calculate a chi^2 to select the best sets of twins. Our results show a competitive performance when compared to other model-dependent methods relying on stellar parameters and isochrones. The power of the method…
