Cool Subdwarf Investigations II: Multiplicity

Abstract

Cool subdwarfs of types K and M are the fainter counterparts of cool main sequence dwarfs that dominate the Galactic population. In this paper we present the results of an optical speckle survey of 62 confirmed cool subdwarf systems within 60 pc. We have resolved two new companions and confirmed two previously known companions with separations 0\farcs13 to 3\farcs29. After including previously known wide companions and all known spectroscopic binaries, we determine the multiplicity rate of cool subdwarfs to be 26$\pm$6%, which is somewhat lower than comparable main sequence stars, which have a multiplicity rate of 37$\pm$5%. We find that only 3% of the cool subdwarfs surveyed have companions within 10 AU, 3% have companions between 10 and 100 AU, and 14% have companions beyond 100 AU. The other 6% of cool subdwarfs are spectroscopic binaries. This is very different from K/M dwarfs that have most companions (13%) at separations closer than 10 AU. However, because a search for close binaries among a large sample of nearby cool subdwarfs remains elusive, it is not yet settled whether or not the multiplicity rates are significantly different. Nonetheless, several different observational results and theories pointing to a possible dearth of subdwarf multiples are discussed.

accepted by AJ

References in corpus (16)

• The Geneva-Copenhagen survey of the Solar neighbourhood: Ages, metallicities, and kinematic properties of 14,000 F and G dwarfs
• The Formation of a Star Cluster: Predicting the Properties of Stars and Brown Dwarfs
• A Catalog of Northern Stars With Annual Proper Motions Larger Than 0.15 Seconds of Arc (LSPM catalog - North)
• M-Subdwarfs: Spectroscopic Classification and the Metallicity Scale
• Catalogue of [Fe/H] determinations for FGK stars : 2001 edition
• Disk and Halo Wide Binaries from the Revised Luyten Catalog: Probes of Star Formation and MACHO Dark Matter
• Binary Stars in the Orion Nebula Cluster
• The Solar Neighborhood XIII: Parallax Results from the CTIOPI 0.9-m Program -- Stars with mu >= 1"/year (MOTION Sample)
• Cool Subdwarf Investigations (CSI) I: New Thoughts for the Spectral Types of K and M Subdwarfs
• Trigonometric Parallaxes for Two Late-Type Subdwarfs: LSR1425+71 (sdM8.0) and the Binary LSR1610-00 (sd?M6pec)
• A CCD Imaging Search for Wide Metal-Poor Binaries
• HST search for M subdwarf binaries
• The Metallicity of Stars with Close Companions
• HST Observations of M Subdwarfs
• Speckle Interferometry of Metal-Poor Stars in the Solar Neighborhood. I
• An astrometric companion to the nearby metal-poor, low-mass star LHS 1589

Cited by in corpus (24)

• A Survey of Stellar Families: Multiplicity of Solar-Type Stars
• Stellar Multiplicity
• The Close Binary Fraction of Solar-type Stars is Strongly Anti-correlated with Metallicity
• The Solar Neighborhood XLV. The Stellar Multiplicity Rate of M Dwarfs Within 25 pc
• CARMENES input catalogue of M dwarfs. I. Low-resolution spectroscopy with CAFOS
• The statistical properties of stars and their dependence on metallicity
• The statistical properties of stars and their dependence on metallicity: the effects of opacity
• The wide binary fraction of solar-type stars: emergence of metallicity dependence at a < 200 AU
• The Exemplar T8 Subdwarf Companion of Wolf 1130
• Stellar loci II. a model-free estimate of the binary fraction for field FGK stars
• The Solar Neighborhood XXIV. Parallax Results from the CTIOPI 0.9-m Program: Stars with $\mu$ $\ge$ 1\farcs0 yr${}^{-1}$ (MOTION Sample) and Subdwarfs
• Know the Star, Know the Planet. II. Speckle Interferometry of Exoplanet Host Stars
• The Origin of the Stellar Mass Distribution and Multiplicity
• Can Ground-based Telescopes Detect The Oxygen 1.27 Micron Absorption Feature as a Biomarker in Exoplanets ?
• The non-monotonic, strong metallicity dependence of the wide-binary fraction
• Multiplicity and period distribution of Population II field stars in solar vicinity
• A spectroscopic and proper motion search of Sloan digital Sky Survey: red subdwarfs in binary systems
• Lucky Imaging of M subdwarfs
• Discovery of New Companions to High Proper Motion Stars from the VVV Survey
• Multiplicity of the Galactic Senior Citizens: A high-resolution search for cool subdwarf companions
• Cool Subdwarf Investigations III: Dynamical Masses of Low Metallicity Subdwarfs
• Multiplicity of stars with planets in the solar neighbourhood
• The Solar Neighborhood XLII. Parallax Results from the CTIOPI 0.9-m Program --- Identifying New Nearby Subdwarfs Using Tangential Velocities and Locations on the H-R Diagram
• Wide companions to M and L subdwarfs with Gaia and the Virtual Observatory