Astrometric Discovery of GJ 164B

Abstract

We discovered a low-mass companion to the M dwarf GJ 164 with the CCD-based imaging system of the Stellar Planet Survey astrometric program. The existence of GJ 164B was confirmed with Hubble Space Telescope NICMOS imaging observations. A high-dispersion spectral observation in V sets a lower limit of Δm>2.2 mag between the two components of the system. Based on our parallax value of 82+/-8 mas, we derive the following orbital parameters: P=2.04+/-0.03 yr, a=1.03+/-0.03, and M_total=0.265+/-0.020 M_solar. The component masses are M_A=0.170+/-0.015 M_solar and M_B=0.095+/-0.015 M_solar. Based on its mass, colors, and spectral properties, GJ 164B has spectral type M6-M8 V.