MACHO PARALLAXES FROM A SINGLE SATELLITE

Massive Compact Objects (MACHOs) are currently being discovered at higher rates than would be expected from standard models of known stellar populations. To determine whether they are due to non-standard distributions of known populations or to an unknown (''dark'') population, one must acquire more information about the individual events. Space-based parallaxes are potentially the best tool for extracting additional information, yielding the ''reduced'' speed upsilon and the direction of relative motion PHI. To leading order, parallax measurements by a single satellite result in a fourfold degeneracy: two possible values of upsilon and two possible signs for PHI. It has been believed that a second satellite would be required to break this degeneracy. I show that the velocity difference between the satellite and the Earth usually allows one to break the degeneracy in upsilon and sometimes also in PHI.