We present a catalog of 99,203 wide binary systems, initially identified as common proper motion (CPM) pairs from a subset of ∼5.2 million stars with proper motions , selected from Gaia data release ...2 (DR2) and the SUPERBLINK high proper motion catalog. CPM pairs are found by searching for pairs of stars with angular separations <1° and proper motion differences . A Bayesian analysis is then applied in two steps. In a first pass, we use proper motion differences and angular separations to distinguish between real binaries and chance alignments. In a second pass, we use parallax data from Gaia DR2 to refine our Bayesian probability estimates. We present a table of 119,390 pairs which went through the full analysis, 99,203 of which have probabilities >95% of being real wide binaries. Of those 99,203 high-probability pairs, we estimate that only about 364 pairs are most likely to be false positives. In addition, we identify 57,506 pairs that have probabilities greater than 10% from the first pass but have high parallax errors and therefore were not vetted in the second pass. We examine the projected physical separation distribution of our highest probability pairs and note that the distribution is a simple exponential tail and shows no evidence of being bimodal. Among pairs with lower probability, wide binaries are detected at larger separations (>104-105 au), consistent with the very wide population suggested in previous studies; however, our analysis suggests that these do not represent a distinct population, but instead represent either the exponential tail of the "normal" wide binary distribution or are simply chance alignments of unrelated field stars. We examine the Hertzsprung-Russell diagram of this set of high-probability wide binaries and find evidence for 980 overluminous components among 2227 K + K wide binaries; assuming these represent unresolved subsystems, we determine that the higher-order multiplicity fraction for K + K wide systems is at least 39.6%.
Abstract
We present a method to identify likely visual binaries in Gaia eDR3 that does not rely on parallax or proper motion. This method utilizes the various point-spread function sizes of Two ...Micron All Sky Survey (2MASS)/Gaia, where at <2.″5 two stars may be unresolved in 2MASS but resolved by Gaia. Due to this, if close neighbors listed in Gaia are a resolved pair, the associated 2MASS source will have a predictable excess in the
J
band that depends on the Δ
G
of the pair. We demonstrate that the expected relationship between 2MASS excess and Δ
G
differs for chance alignments, as compared to true binary systems, when parameters like magnitude and location on the sky are also considered. Using these multidimensional distributions, we compute the likelihood of a close pair of stars to be a chance alignment, resulting in a total(clean) catalog of 68,725(50,230) likely binaries within 200 pc with a completeness rate of ∼75%(∼64%) and contamination rate of ∼14%(∼0.4%). Within this, we find 590 previously unidentified binaries from Gaia eDR3 with projected physical separations <30 au, where 138 systems were previously identified, and for
s
< 10 au we find that 4 out of 15 new likely binaries have not yet been observed with high-resolution imaging. We also demonstrate the potential of our catalog to determine physical separation distributions and binary fraction estimates, from this increase in low-separation binaries. Overall, this catalog provides a good complement for the study of local binary populations by probing smaller physical separations and mass ratios, and provides prime targets for speckle monitoring.
We have calculated Fe and Ti abundances in 12 low-metallicity main sequence M stars using high-resolution spectra. These subdwarf and extreme-subdwarf stars allow us to extend our calibration of a ...method to determine cool-dwarf-star metallicities using molecular band strength indices from low-resolution spectra. Our calibration can now be used to determine metallicity to within± 0.3 dex
±
0.3
dex
for stars with Fe/H between-1.5
-
1.5
and+0.05
+
0.05
and temperatures between 3500 and 4000 K. We also report a method to estimate temperatures for M dwarfs using equivalent width measurements of the infrared Ca II triplet and the K I line at 7699 Å. Our metallicity measurements show that the recently proposed classification system for low-mass stars (dwarfs, subdwarfs, extreme subdwarfs, and ultrasubdwarfs) does represent a metallicity sequence, with the ultrasubdwarfs the most metal-poor stars.
ABSTRACT
We combine photometric metallicities with astrometry from Gaia DR3 to examine the chemodynamic structure of ∼250 000 K dwarfs in the solar neighbourhood (SN). In kinematics, we observe ...ridges/clumps of ‘kinematic groups’, like studies of more massive main-sequence stars. Here, we note clear differences in both metallicity and vertical velocity as compared with the surrounding regions in velocity space and hypothesize this is due to differences in mean age. To test this, we develop a method to estimate the age distribution of subpopulations of stars. In this method, we use GALAH data to define probability distributions of W versus M/H in age bins of 2 Gyr and determine optimal age distributions as the best-fitting weighted sum of these distributions. This process is then validated using the GALAH subset. We estimate the probable age distribution for regions in the kinematic plane, where we find significant substructure that is correlated with the kinematic groups. Most notably, we find an age gradient across the Hercules streams that is correlated with birth radius. Finally, we examine the bending and breathing modes as a function of age. From this, we observe potential hints of an increase in the bending amplitude with age, which will require further analysis in order to confirm it. This is one of the first studies to examine these chemodynamics in the SN using primarily low-mass stars and we hope these findings can better constrain dynamical models of the Milky Way due to the increase in resolution the sample size provides.
A search of the Sloan Digital Sky Survey spectroscopic database has turned up 23 new ultracool subdwarfs, low-mass metal-poor stars of spectral subtype M 7.0 or later. Spectra from these red objects ...all show very strong molecular bands of CaH but relatively weak bands of TiO, indicative of a cool, metal-poor atmosphere. Five of the stars are formally classified as M subdwarfs (sdM7.0-sdM8.5), 13 as more metal-poor extreme subdwarfs (esdM7.0-esdM8.0), and five as extremely metal-poor ultra subdwarfs (usdM7.0-usdM7.5). In the H sub(r), r - z reduced proper motion diagram, these subdwarfs clearly populate the locus of low-luminosity stars with halo kinematics. It is argued that the objects are all very low mass, metal-poor stars from the Galactic halo (Population II). These new discoveries more than double the census of spectroscopically confirmed ultracool subdwarfs. We show that the stars stand out remarkably in the g - r, r - i color-color diagram; a proposed color and proper motion selection scheme is expected to be extremely efficient in identifying more of these old, very low mass stars in the vicinity of the Sun.
We constrain the densities of Earth- to Neptune-size planets around very cool (T sub(e) = 3660-4660 K) Kepler stars by comparing 1202 Keck/HIRES radial velocity measurements of 150 nearby stars to a ...model based on Kepler candidate planet radii and a power-law mass-radius relation. Our analysis is based on the presumption that the planet populations around the two sets of stars are the same. The model can reproduce the observed distribution of radial velocity variation over a range of parameter values, but, for the expected level of Doppler systematic error, the highest Kolmogorov-Smirnov probabilities occur for a power-law index alpha approx = 4, indicating that rocky-metal planets dominate the planet population in this size range. A single population of gas-rich, low-density planets with alpha = 2 is ruled out unless our Doppler errors are > or =, slanted5 m s super(-1), i.e., much larger than expected based on observations and stellar chromospheric emission. If small planets are a mix of gamma rocky planets ( alpha = 3.85) and 1 - gamma gas-rich planets ( alpha = 2), then gamma > 0.5 unless Doppler errors are > or =, slanted4 m s super(-1). Our comparison also suggests that Kepler's detection efficiency relative to ideal calculations is less than unity. One possible source of incompleteness is target stars that are misclassified subgiants or giants, for which the transits of small planets would be impossible to detect. Our results are robust to systematic effects, and plausible errors in the estimated radii of Kepler stars have only moderate impact.
A total of 573 objects have previously been identified as high velocity stars. We are using existing Gaia data to confirm their status as such. We are then conducting a systematic survey of the ...entire Gaia DR3 catalog to identify previously unknown high velocity stars. Of particular interest to us is the prospect of detecting planetary companions, which has yet to be discovered. We will attempt to observe these companions via the transit method aided by TESS data.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Abstract
We present a Bayesian method to cross-match 5,827,988 high proper-motion Gaia sources (
μ
> 40 mas yr
−1
) to various photometric surveys: Two Micron All Sky Survey, AllWISE data release ...from the Wide-field Infrared Explorer (WISE) mission, Galaxy Evolution Explorer, Radial Velocity Experiment, Sloan Digital Sky Survey, and Panoramic Survey Telescope and Rapid Response System (Pan-STARRS). To efficiently associate these objects across catalogs, we develop a technique that compares the multidimensional distribution of all sources in the vicinity of each Gaia star to a reference distribution of random field stars obtained by extracting all sources in a region on the sky displaced 2′. This offset preserves the local field stellar density and magnitude distribution, allowing us to characterize the frequency of chance alignments. The resulting catalog with Bayesian probabilities >95% has a marginally higher match rate than current internal Gaia data release 2 (DR2) matches for most catalogs. However, a significant improvement is found with Pan-STARRS, where ∼99.8% of the sample within the Pan-STARRS footprint is recovered, as compared to a low ∼20.8% in Gaia DR2. Using these results, we train a Gaussian process regressor to calibrate two photometric metallicity relationships. For dwarfs of 3500 <
T
eff
< 5280 K, we use metallicity values of 4378 stars from the Apache Point Observatory Galactic Evolution Experiment and Hejazi et al. to calibrate the relationship, producing results with a 1
σ
precision of 0.12 dex and few systematic errors. We then indirectly infer the metallicity of 4018 stars with 2850 <
T
eff
< 3500 K, which are wide companions of primaries whose metallicities are estimated with our first regressor, to produce a relationship with a 1
σ
precision of 0.21 dex and significant systematic errors. Additional work is needed to better remove unresolved binaries from this second sample to reduce these systematic errors.
We perform a search for faint, common proper motion companions of Hipparcos stars using the recently published Lepine-Shara Proper Motion-North catalog of stars with proper motion m > 0.15'' yr-1. ...Our survey uncovers a total of 521 systems with angular separations 3'' < plus or minus < 1500'', with 15 triples and 1 quadruple. Our new list of wide systems with Hipparcos primaries includes 130 systems identified here for the first time, including 44 in which the secondary star has V > 15.0. Our census is statistically complete for secondaries with angular separations 20'' < plus or minus < 300'' and apparent magnitudes V < 19.0. Overall, we find that at least 9.5% of nearby (d < 100 pc) Hipparcos stars have distant stellar companions with projected orbital separations s > 1000 AU. We observe that the distribution in orbital separations is consistent with Opik's law, f(s) ds ~ s-1 ds, only up to a separation s 4000 AU, beyond which it follows a more steeply decreasing power law f(s) ds ~ s-l ds with l = 1.6 ± 0.1. We also find that the luminosity function of the secondaries is significantly different from that of the single stars' field population, showing a relative deficiency in low-luminosity (8 < MV < 14) objects. The observed trends suggest either a formation mechanism biased against low-mass companions, or a disruption over time of systems with low gravitational binding energy.
Abstract
We present a model-fit pipeline to determine the stellar parameters of M-type dwarfs, which is an improvement on our previous work described in Hejazi et al. We apply this pipeline to ...analyze the low-resolution (
R
∼ 2000) spectra of 3745 M dwarfs/subdwarfs, collected at the MDM Observatory, Lick Observatory, Kitt Peak National Observatory, and Cerro Tololo Inter-American Observatory. We examine the variation of the inferred parameter values in the H-R diagram constructed from their Gaia Early Data Release 3 (EDR3) parallaxes and optical magnitudes. We also study the distribution of our stars in the abundance diagram of
α
/Fe versus M/H and inspect the variation of their metallicity class, effective temperature, and surface gravity, as well as their Galactic velocity components
U
,
V
, and
W
, in this diagram. In addition, the analyses of the stars’ projected motions in the two-dimensional
UV
,
VW
, and
UW
planes, the variation of their chemical parameters in these planes, and their distribution in the abundance−velocity diagrams are important parts of this study. The precision of our model-fit pipeline is confirmed by the clear stratification of effective temperature and chemical parameters in the H-R diagram; the similarity of the stars’ distribution in the
α
/Fe versus M/H diagram and in the metallicity−velocity planes to those from other studies; the revealing of substructure in the abundance−velocity diagrams; and chemical homogeneity between the components of a set of binary systems.
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