MULTIPLICITY-CORRECTED MASS FUNCTION OF MAIN-SEQUENCE STARS IN THE SOLAR NEIGHBORHOOD

The present-day mass function (PDMF) of stars in the solar neighborhood has been derived after correcting the photometric luminosity function for the effects of unresolved multiple stellar systems. Such a PDMF gives a stellar surface mass density of 39.5 M. pc-2 as opposed to only 31.3 M. pc-2 given by the PDMF not corrected for the effects of stellar multiplicity. We have also calculated the initial mass function (IMF) of stars from the corrected PDMF using a number of star-formation rates with exponential time dependence-a form which gives good fits to data on chemical evolution. We find that the neutron star and white dwarf formation rates restrict the reciprocal of the time constant of star formation to the range between -0.1 and +0.1 Gyr-1. The IMF for stellar masses greater than 1.4 M. can be represented as a power law with an exponent of -1.56 +/- 0.05. However, for masses greater than 6.5 M., a power of -1.67 fits better. The ratio of the mass of gas returned to the ISM by the stars to the total mass of gas that has ever gone into star formation-the returned fraction-is found to be a rapidly increasing function of the reciprocal of the time constant of star formation. The fraction of remnants and evolved stars also show the same trend, but the increase is not as rapid. The total surface mass density predicted by the IMF is consistent with the presence of very little or no nonbaryonic dark matter in the Galactic disk in the solar neighborhood.