Ultra-wide, Low-mass Binaries: Constraints on Binary Formation Theory and Calibration of Fundamental Stellar Parameters

Details Ultra-wide, Low-mass Binaries: Constraints on Binary Formation Theory and Calibration of Fundamental Stellar Parameters Ultra-wide, Low-mass Binaries: Constraints on Binary Formation Theory and Calibration of Fundamental Stellar Parameters

Jan 2012

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2012aas...21913205d&link_type=abstract

American Astronomical Society, AAS Meeting #219, #132.05

Mathematics

Probability

Scientific paper

We present results from the Sloan Low-mass Wide Pairs of Kinematically Equivalent Stars (SLoWPoKES) catalog of ultra-wide (103--105 AU), low-mass (K5--M7) common proper motion binaries. With 1342 disk dwarf, subdwarf, and white dwarf-red dwarf systems, this is the largest catalog of low-mass, wide binaries. A Galactic model, based on empirical stellar number density and space velocity distributions, was constructed to select only bona fide pairs with probability of chance alignment <5%, making SLoWPoKES an efficient sample for followup observations. We find in SLoWPoKES the presence of two populations of wide binaries, with a break at separations of 0.1 pc: tightly bound systems that are expected to last 10 Gyr or longer and wide, weakly bound systems that are expected to dissipate within a few Gyr (based on binary disruption timescales from dynamical calculations). With physical separation as large as a parsec, the widest pairs may have been formed from evaporating stars during the dissipation of star-forming clusters. Based on our followup LGS-AO imaging observations of SLoWPoKES pairs, we found an overall higher-order multiplicity fraction of 45%. However, it is a strong function of binary separation: the fraction increases from 21% at the smaller wide binary separations to 77% at the largest separations, indicating that small N-body dynamics are important in explaining the formation of tight binaries.
From spectroscopic followup of 113 pairs, we confirm that the Lepine et al. zeta-index traces iso-metallicity loci for most of our sample of M dwarfs. However, we find a small systematic bias in zeta, especially in the early-type M dwarfs. We use our sample to recalibrate the definition of zeta. While representing a small change in the definition, the new zeta is a significantly better predictor of iso-metallicity for the higher mass M dwarfs.

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