OBSERVATIONAL LIMITS ON OMEGA IN STARS, BROWN DWARFS, AND STELLAR REMNANTS FROM GRAVITATIONAL MICROLENSING

Microlensing by compact objects with masses between approximately 0.001 M. and approximately 300 M. will amplify the continuum emission of a quasar, without significantly changing its line emission. Thus, compact objects with masses associated with stars, subdwarfs, and stellar remnants will reduce the apparent equivalent widths of quasar emission lines. It is possible to detect this population of lenses by searching for an increase in the number of small equivalent width quasars with redshift. This increase was looked for, but not found, in quasar samples taken from the Einstein Medium Sensitivity Survey and the Steidel & Sargent absorption-line studies. Thus, OMEGA(c), the cosmological density of compact objects relative to the critical density, is less than or similar to 0.1 in the mass range 0.01 M.-20 M. (for OMEGA < 0.6). For any value of OMEGA, OMEGA(c), less than or similar to 0.2 in the larger mass range 0.001 M.-60 M., and OMEGA(c) < 1 for 0.001 M.-300 M.. Subdwarfs, stellar objects, or their remnants (e.g., MACHOS) cannot close the universe.