An adaptive optics survey of M6.0-M7.5 Stars: Discovery of three very low mass binary systems including two probable hyades members

Nick Siegler, Laird M Close, Eric E. Mamajek, Melanie Freed

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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 < 0.185 M) 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 5-2+4% 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 -0.10+0.009 and 0.082-0.009+0.009 M.

Original languageEnglish (US)
Pages (from-to)1265-1276
Number of pages12
JournalAstrophysical Journal
Issue number2 I
Publication statusPublished - Dec 1 2003



  • Binaries: general
  • Stars: low-mass, brown dwarfs

ASJC Scopus subject areas

  • Space and Planetary Science

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