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HST/FGS Trigonometric Parallaxes of M-dwarf Eclipsing Binaries

van Belle, G.; Schaefer, G.; von Braun, K., Nelan, E., Hartman, Zachary, Boyajian, T., Lopez-Morales, M., Ciardi, D.

PASP, 2020

Hubble Space Telescope (HST) Fine Guidance Sensor (FGS) trigonometric parallax observations were obtained to directly determine distances to five nearby M-dwarf/M-dwarf eclipsing binary systems. These systems are intrinsically interesting as benchmark systems for establishing basic physical parameters for low-mass stars, such as luminosity L, and radius R. HST/FGS distances are also one of the few direct checks on Gaia trigonometric parallaxes, given the comparable sensitivity in both magnitude limit and determination of parallactic angles. A spectral energy distribution (SED) fit of each system’s blended flux output was carried out, allowing for estimation of the bolometric flux from the primary and secondary components of each system. From the stellar M, L, and R values, the low-mass star relationships between L and M, and R and M, are compared against idealized expectations for such stars. An examination on the inclusion of these close M-dwarf/M-dwarf pairs in higher-order common proper motion (CPM) pairs is analyzed; each of the 5 systems has indications of being part of a CPM system. Unexpected distances on interesting objects found within the grid of parallactic reference stars are also presented, including a nearby M dwarf and a white dwarf.

The SUPERWIDE Catalog: A Catalog of 99,203 Wide Binaries Found in Gaia and Supplemented by the SUPERBLINK High Proper Motion Catalog

Hartman, Z. and Lepine, S.

ApJS, 2020

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 μ > 40 mas yr-1, 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 ∆μ < 40 mas yr-1. 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%.