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The Murky Depths of the Main Sequence: Nearby Speckled Dwarfs and Elusive Brown Beasts

Published online by Cambridge University Press:  12 April 2016

Todd J. Henry  and
Donald W. McCarthy Jr.
Todd J. Henry
Affiliation:
Steward Observatory, University of Arizona, Tucson AZ 85721, USA
Donald W. McCarthy Jr.
Affiliation:
Steward Observatory, University of Arizona, Tucson AZ 85721, USA

Abstract

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Using infrared speckle imaging techniques, we have completed a comprehensive survey of all northern (δ ≥ −25°) M dwarfs within 8 parsecs for low mass companions. Of the 74 targets searched, six new companions were found. Included in the final census are four objects orbiting their primaries at sub-arcsecond separations which have masses near 80 Jupiters, making them viable brown dwarf candidates. Three of these — LHS 1047B, GL 623B and G 208-44B — are the faintest red objects for which masses have been determined and represent the limit of our current knowledge about the faint end of the mass-luminosity relation.

The complete sample includes 99 members, and under further analysis reveals fundamental facts about the red dwarf population that were unknown until the present study: 1) 30-40 % of M dwarf primaries have companions, 2) more companions are found orbiting 1-10 AU from the primary than in any other decade interval, and 3) there are 50% fewer red dwarfs known in the more distant half of the survey volume, presumably because the parallax and proper motion surveys are incomplete.

In addition, we find that the infrared luminosity function (LF) is fiat or rising toward the end of the main sequence, while the visible LF may be flat, and we illustrate that the determination of an accurate LF is critically sensitive to the resolution of binaries. A better description of the stellar population, the mass function, is found to be undoubtedly rising to the stellar/substellar break. Finally, we have developed a much-needed mass-luminosity relation for stars of mass 1.2 to 0.08 M⊙, and using these relations find that the M dwarfs contribute ~0.2 M⊙/pc3 to the galactic mass.

Type
Pre-Main Sequence & Young Binaries
Information
International Astronomical Union Colloquium , Volume 135: Complementary Approaches to Double and Multiple Star Research , 1992 , pp. 10 - 20
Copyright
Copyright © Astronomical Society of the Pacific 1992

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