MACHO PHOTOMETRY AND ASTROMETRY

MACHOs have been discovered by their relativistic amplification of lig ht from distant stars as they crossed very close to the line-of-sight. The very few events were detected from more than a milliard photometr ic measurements of millions of stars in the LMC. - A mathematical theo ry of analysis of astrometric and photometric measurements of microlen sing events is presented. It is shown that three photometric measureme nts and three one-dimensional astrometric measurements during an event are, in principle, sufficient to determine the - precisely - six obse rvable physical parameters of the MA-CHO, including the proper motion and distance of the dark body, provided the position, motion and dista nce of the undeflected star has been determined from observations outs ide the event. The practical possibility of such observations is discu ssed by comparison with the proposed ROEMER satellite, an instrument c oncept with the potential for obtaining the many milliards of photomet ric and astrometric observations of the required quality. At least 300 photometric amplifications of light from stars brighter than V = 16.5 mag could de detected during a ROEMER mission, but the prospects for significant astrometric observations are meagre.