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 (STEPS) 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 delta m> 2.2 mag between the two components of the system. Based upon our parallax value of 0.082 +/- 0.008, we derive the following orbital parameters: P = 2.04 +/- 0.03 y, a = 1.03 +/- 0.03 AU, and Mtotal = 0.265 +/- 0.020 MSun. The component masses are MA = 0.170 +/- 0.015 MSun and MB = 0.095 +/- 0.015 MSun. Based on its mass, colors, and spectral properties, GJ 164B has spectral type M6-8 V.