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.
Abstract Here we present speckle observations of 16 low-separation ( s < 30 au) high-probability candidate binaries from the catalog by Medan et al., where secondaries typically lack astrometric ...solutions in Gaia. From these speckle observations, we find a second component is always detected within the field of view. To determine if the detection is consistent with a physical companion or a chance alignment with a background source, we utilize a statistic from Tokovinin & Kiyaeva that compares the apparent motion of the systems to the expected orbital motion ( μ ′ ). Using simulated binary orbits, we construct likelihood distributions of μ ′ assuming various total errors on the measurements. With the hypothesis that the system is a true binary, we show that large measurement errors can result in μ ′ values higher than expected for bound systems. Using simulated chance alignments, we also create similar likelihoods to test this alternative hypothesis. By combining likelihoods of both true binaries and chance alignments, we find that 15 of the 16 candidates are physical systems regardless of the level of measurement error. Our findings also accommodate all 16 as physical systems if the average, relative measurement error on the binary separations and position angles is ∼4.3%, which is consistent with our knowledge of the Gaia and Gemini speckle pipelines. Importantly, beyond assessing the likelihood of a true binary versus chance alignment, this quantitative assessment of the true average measurement error will allow more robust error estimates of mass determinations from short separation binaries with Gaia and/or Gemini speckle data.
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.
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 present a catalog of 531 white dwarf candidates that have large apparent transverse motions relative to the Sun ( km s−1), thus making them likely members of the local Galactic halo population. ...The candidates were selected from the Gaia Data Release 2 and are located in a great circle with 20° width running across both Galactic poles and the Galactic center and anticenter, a zone that spans 17.3% of the sky. The selection used a combination of kinematic and photometric properties, derived primarily from Gaia proper motions, G magnitudes, and color, and including parallax whenever available. Additional validation of the white dwarf candidates is made using PanSTARRS photometric (gri) data. Our final catalog includes not only stars having full kinematic and luminosity estimates from reliable Gaia parallax, but also stars with presently unreliable or no available Gaia parallax measurements. We argue that our method of selecting local halo objects with and without reliable parallax data leads us to round up all possible halo white dwarfs in the Gaia catalog (in that particular section of the sky) with recorded proper motions mas yr−1 and that pass our km s−1 threshold requirement. We expect this catalog will be useful for the study of the white dwarf population of the local Galactic halo.
Abstract
Over the past decade, the number of known wide-binary systems has expanded exponentially, thanks to the release of data from the Gaia Mission. Some of these wide-binary systems are actually ...higher-order multiples, where one of the components is an unresolved binary itself. One way to search for these systems is by identifying the overluminous components in the systems. In this study, we examine 4947 K+K wide-binary pairs from the SUPERWIDE catalog, and quantify the relative colors and luminosities of the components to find evidence for additional unresolved companions. The method is best illustrated in a graph that we call the “Lobster” diagram. To confirm that the identified overluminous components are close binary systems, we cross-match our wide binaries with the TESS, K2, and Kepler archives, and search for signs of eclipses and fast stellar rotation modulation in the light curves. We find that 78.9% ± 20.7% of the wide binaries that contain an eclipsing system are identified as overluminous in the “Lobster” diagram, and that 73.5% ± 12.4% of the wide binaries that contain a component showing fast rotation (
P
< 5 days) also show an overluminous component. From these results, we calculate a revised lower limit on the higher-order multiplicity fraction for K+K wide binaries of 40.0% ± 1.6%. We also examine the higher-order multiplicity fraction as a function of projected physical separation and metallicity. The fraction is unusually constant as a function of projected physical separation, while we see no statistically significant evidence that the fraction varies with metallicity.
Optical and infrared continuum polarization from the interstellar medium is known to generally be due to irregular dust grains aligned with the magnetic field. This provides an important tool to ...probe the geometry and strength of those fields, particularly if the variations in the grain alignment efficiencies can be understood. Here, we examine polarization variations observed throughout the wall of the Local Bubble, using a large polarization survey of the North Galactic cap (b > 30°) from Berdyugin et al. These data are analyzed together with archival photometric and spectroscopic data along with the mapping of the Local Bubble by Lallement et al. We can model the observational data by assuming that the mechanism driving alignment is due to the radiation from the surrounding star field. In particular we find that the fractional polarization is dominated by the light from the OB associations within 200 pc of the Sun, but is largely insensitive to the radiation field from red field stars. This behavior is consistent with the expected wavelength dependence of radiative grain alignment theory. We also probe the relative strength of the magnetic field in the wall of the Local Bubble using the Davis-Chandrasekhar-Fermi method. We find evidence for a systematically varying field strength distribution, where the variations in the field are correlated with the variations in grain alignment efficiency, indicating that the regions of relatively higher field strength might represent a compression of the wall by the interaction of the outflow in the Local Bubble and the opposing flows from the surrounding OB associations.
Dust-induced polarization in the interstellar medium (ISM) is due to asymmetric grains aligned with an external reference direction, usually the magnetic field. For both the leading alignment ...theories, the alignment of the grain's angular momentum with one of its principal axes and the coupling with the magnetic field requires the grain to be paramagnetic. Of the two main components of interstellar dust, silicates are paramagnetic, while carbon dust is diamagnetic. Hence, carbon grains are not expected to align in the ISM. To probe the physics of carbon grain alignment, we have acquired Stratospheric Observatory for Infrared Astronomy/Higch-resolution Airborne Wideband Camera-plus far-infrared photometry and polarimetry of the carbon-rich circumstellar envelope (CSE) of the asymptotic giant branch star IRC+10 degrees 216. The dust in such CSEs are fully carbonaceous and thus provide unique laboratories for probing carbon grain alignment. We find a centrosymmetric, radial, polarization pattern, where the polarization fraction is well correlated with the dust temperature. Together with estimates of a low fractional polarization from optical polarization of background stars, we interpret these results to be due to a second-order, direct radiative external alignment of grains without internal alignment. Our results indicate that (pure) carbon dust does not contribute significantly to the observed ISM polarization, consistent with the nondetection of polarization in the 3.4 mu m feature due to aliphatic CH bonds on the grain surface.
Abstract
Dust-induced polarization in the interstellar medium (ISM) is due to asymmetric grains aligned with an external reference direction, usually the magnetic field. For both the leading ...alignment theories, the alignment of the grain’s angular momentum with one of its principal axes and the coupling with the magnetic field requires the grain to be paramagnetic. Of the two main components of interstellar dust, silicates are paramagnetic, while carbon dust is diamagnetic. Hence, carbon grains are not expected to align in the ISM. To probe the physics of carbon grain alignment, we have acquired Stratospheric Observatory for Infrared Astronomy/Higch-resolution Airborne Wideband Camera-plus far-infrared photometry and polarimetry of the carbon-rich circumstellar envelope (CSE) of the asymptotic giant branch star IRC+10° 216. The dust in such CSEs are fully carbonaceous and thus provide unique laboratories for probing carbon grain alignment. We find a centrosymmetric, radial, polarization pattern, where the polarization fraction is well correlated with the dust temperature. Together with estimates of a low fractional polarization from optical polarization of background stars, we interpret these results to be due to a second-order, direct radiative external alignment of grains without internal alignment. Our results indicate that (pure) carbon dust does not contribute significantly to the observed ISM polarization, consistent with the nondetection of polarization in the 3.4
μ
m feature due to aliphatic CH bonds on the grain surface.
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 PSF sizes of 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 \(\Delta G\) of the pair. We demonstrate that the expected relationship between 2MASS excess and \(\Delta G\) 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 \(\sim75\%\)(\(\sim64\%\)) and contamination rate of \(\sim14\%\)(\(\sim0.4\%\)). 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.
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