Jj. Dalcanton et al., OBSERVATIONAL LIMITS ON OMEGA IN STARS, BROWN DWARFS, AND STELLAR REMNANTS FROM GRAVITATIONAL MICROLENSING, The Astrophysical journal, 424(2), 1994, pp. 550-568
Microlensing by compact objects with masses between approximately 0.00
1 M. and approximately 300 M. will amplify the continuum emission of a
quasar, without significantly changing its line emission. Thus, compa
ct objects with masses associated with stars, subdwarfs, and stellar r
emnants 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 sampl
es taken from the Einstein Medium Sensitivity Survey and the Steidel &
Sargent absorption-line studies. Thus, OMEGA(c), the cosmological den
sity 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 l
arger 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 c
lose the universe.