Astrophys. J., 757, 110 (2012/October-1)
Discovery of a very low mass triple with late-M and T dwarf components: LP 704-48/SDSS J0006-0852AB.
BURGASSER A.J., LUK C., DHITAL S., BARDALEZ GAGLIUFFI D., NICHOLLS C.P., PRATO L., WEST A.A. and LEPINE S.
Abstract (from CDS):
We report the identification of the M9 dwarf SDSS J000649.16-085246.3 as a spectral binary and radial velocity (RV) variable with components straddling the hydrogen-burning mass limit. Low-resolution near-infrared spectroscopy reveals spectral features indicative of a T dwarf companion, and spectral template fitting yields component types of M8.5±0.5 and T5±1. High-resolution near-infrared spectroscopy with Keck/NIRSPEC reveals pronounced RV variations with a semi-amplitude of 8.2±0.4 km/s. From these we determine an orbital period of 147.6±1.5 days and eccentricity of 0.10±0.07, making SDSS J0006-0852AB the third tightest very low mass binary known. This system is also found to have a common proper motion companion, the inactive M7 dwarf LP 704-48, at a projected separation of 820±120 AU. The lack of Hα emission in both M dwarf components indicates that this system is relatively old, as confirmed by evolutionary model analysis of the tight binary. LP 704-48/SDSS J0006-0852AB is the lowest-mass confirmed triple identified to date, and one of only seven candidate and confirmed triples with total masses below 0.3 M☉ currently known. We show that current star and brown dwarf formation models cannot produce triple systems like LP 704-48/SDSS J0006-0852AB, and we rule out Kozai-Lidov perturbations and tidal circularization as a viable mechanism to shrink the inner orbit. The similarities between this system and the recently uncovered low-mass eclipsing triples NLTT 41135AB/41136 and LHS 6343ABC suggest that substellar tertiaries may be common in wide M dwarf pairs.
binaries: spectroscopic - binaries: visual - brown dwarfs - stars: individual: (SDSS J000649.16-085246.3, LP 704-48) - stars: fundamental parameters - stars: low-mass
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