Brown Dwarf Companions to G-type Stars. I: Gliese 417B and Gliese 584C

Abstract

We present astrometric and spectroscopic observations confirming that two nearby G dwarf systems (Gliese 417 = BD+36 2162 and Gliese 584AB = eta CrB AB) have a widely separated, L dwarf, substellar companion. Using age estimates of the G dwarf primaries, we estimate masses for these L dwarfs from theoretical evolutionary tracks. For the L4.5 dwarf Gl 417B we estimate an age of 0.08-0.3 Gyr and a mass of 0.035+/-0.015 M_sun. For the L8 dwarf Gl 584C we estimate an age of 1.0-2.5 Gyr and a mass of 0.060+/-0.015 M_sun. This latter object also shows evidence of spectrum variability, which may be due to surface inhomogeneities rotating into and out of view. These new companions are also compared to six other L dwarf and T dwarf companions previously recognized. For the L dwarf companions, ages implied by the presence or absence of lithium are consistent with ages inferred from the primaries alone.

37 pages plus 9 tables, accepted for the June 2001 issue of AJ

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