Astrometry of the low-luminosity stars VB8 and VB10.

Observations of the very low luminosity stars VB8 and VB10 made over a ten-year period as part of the parallax program of the US Naval Observatory are reported, with broadband photometric and PVI-color-measurements data from two nights. Plates (63 for VB8 and 87 for VB10) exposed singly for about 1 hour were measured using a semiautomatic measuring machine; relative parallax was calculated using standard linear parallax solutions and corrected statistically to absolute parallax on the basis of apparent V magnitude. Absolute parallax and estimated mass were found to be 0.154 + or 0.006 arcsec and 0.045 solar mass for VB8, and 0.174 + or 0.005 arcsec and 0.033 solar mass for VB10. Preliminary calculations of period and mass are presented for the unseen, very faint companion stars probably responsible for perturbations observed in the motion of both stars.