Discovery of Two Very Low Mass Binaries: Final Results of an Adaptive Optics Survey of Nearby M6.0-M7.5 Stars

Siegler, Nick; Close, Laird M.; Cruz, Kelle L.; Martín, Eduardo L.; Reid, I. Neill
Referencia bibliográfica

The Astrophysical Journal, Volume 621, Issue 2, pp. 1023-1032.

Fecha de publicación:
3
2005
Número de autores
5
Número de autores del IAC
1
Número de citas
91
Número de citas referidas
87
Descripción
We present updated results of a high-resolution, magnitude-limited (Ks<12 mag) imaging survey of nearby low-mass M6.0-M7.5 field stars. The observations were carried out using adaptive optics at the Gemini North, VLT, Keck II, and Subaru telescopes. Our sample of 36 stars consists predominantly of nearby (<~30 pc) field stars, five of which we have resolved as binaries. Two of the binary systems, 2MASSI J0429184-312356 and 2MASSI J1847034+552243, are presented here for the first time. All five of the discovered binary systems have separations between 0.08" and 0.53" (2-9 AU) with similar mass ratios (q>0.8, ΔKs<1 mag). This result supports the hypothesis that wide (a>20 AU), very low mass (VLM; Mtot<0.19Msolar) binary systems are rare. The projected semimajor axis distribution of these systems peak at ~5 AU, and we report a sensitivity-corrected binary fraction of 9+4-3% for stars with primaries of spectral type M6.0-M7.5 with separations >~3 AU and mass ratios q>~0.6. Within these instrumental sensitivities, these results support the overall trend that both the semimajor axis distribution and binary fraction are a function of the mass of the primary star and decrease with decreasing primary mass. These observations provide important constraints for low-mass binary star formation theories.