Hubble Space Telescope astrometric observations of the metal-poor spectroscopic binary HD 20039

An attempt has been made to spatially resolve the metal-poor, double-lined spectroscopic binary HD 20039 with the Hubble Space Telescope Fine Guidance System. Astrometric measurements of the system to complement the spectroscopic orbit would permit the distance and the masses of the components to be determined. Observations were obtained around the times of predicted maximum separation on both sides of the orbit, but the system was not resolved. The resulting upper limit on the separation indicates that the distance to HD 20039 is significantly larger than expected from its assumed classification as a subdwarf.