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Title:
An Adaptive Optics Survey of M6.0-M7.5 Stars: Discovery of Three Very Low Mass Binary Systems Including Two Probable Hyades Members
Authors:
Siegler, Nick; Close, Laird M.; Mamajek, Eric E.; Freed, Melanie
Affiliation:
AA(Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721; ), AB(Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721; ), AC(Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721; ), AD(Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721; )
Publication:
The Astrophysical Journal, Volume 598, Issue 2, pp. 1265-1276. (ApJ Homepage)
Publication Date:
12/2003
Origin:
UCP
ApJ Keywords:
Stars: Binaries: General, Instrumentation: Adaptive Optics, Galaxy: Open Clusters and Associations: Individual: Name: Hyades, Stars: Individual: Alphanumeric: LP 415-20, Stars: Individual: Alphanumeric: LP 475-855, Stars: Individual: Alphanumeric: 2MASSW J1750129+442404, Stars: Low-Mass, Brown Dwarfs
DOI:
10.1086/378935
Bibliographic Code:
2003ApJ...598.1265S

Abstract

A survey of 30 nearby M6.0-M7.5 dwarfs with Ks<12 mag utilizing the Hokupa`a adaptive optics system at the Gemini North Telescope has discovered three new binary systems. All three systems have separations between 0.12" and 0.29" (3-10 AU) with similar mass ratios (q>0.8, ΔKs<0.7). This result gives further support to the suggestion that wide (a>20 AU), very low mass (Mtot<0.185Msolar) binary systems are exceedingly rare or perhaps even nonexistent. The semimajor axis distribution of these systems peaks at ~5 AU, tighter than more massive M and G binary distributions, which have a broad peak at separations of ~30 AU. We find a sensitivity-corrected binary fraction in the range 5+4-2% for M6.0-M7.5 stars with separations a>3 AU. This binary frequency is less than the ~32% measured among early M dwarfs over the same separation range. Two of the low-mass binaries are probable Hyades open cluster members based on proper motions, cluster membership probabilities, radial velocities, and near-IR photometry. LP 415-20 has the distinction of being the tightest (3.6 AU) multiple system ever spatially resolved in the cluster, and the companions of LP 415-20 and LP 475-855 are among the least massive objects ever resolved in the Hyades, with estimated masses of 0.081+0.009-0.010 and 0.082+0.009-0.009 Msolar.
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