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A. A. Muench, E. A. Lada, C. J. Lada (U.Florida)
We now know that the process of star formation results in freely-floating objects with masses spanning nearly four orders of magnitude. However, both the distribution of these objects' masses at birth and the precise physics responsible for the shape of this initial mass function (IMF) are poorly known and can be improved upon by focusing on very young star clusters just emerging from their parental molecular clouds. For this reason we have investigated the usefulness of a very young cluster's luminosity function as a tool for deriving that cluster's underlying mass function. Through the development of a detailed Monte Carlo-based population synthesis algorithm for embedded pre-main sequence stars and the application of this algorithm to the products of deep near-infrared surveys of three young (1-5 Myr) clusters, we find that a young cluster's luminosity function is an excellent probe of that cluster's initial mass function over the entire range of stellar and substellar mass. From our construction and analysis of the near-infrared luminosity functions of the NGC 2362, IC 348 and Trapezium clusters, we find that these clusters display remarkably similar underlying mass functions, all forming broad peaks between 0.1 and 0.3 times the mass of the Sun; deeper observations of the latter two clusters reveal an IMF that turns over and declines throughout the brown dwarf regime. Thus, we find that brown dwarfs do not dominate stars either by number or total mass. Lastly, we use a statistically significant sample of candidate brown dwarfs to show that these objects appear as likely to have been born with circumstellar disks as stars. Combining this finding with the continuity of the shape of the initial mass function across numerous environments suggests that a single physical mechanism may dominate the star formation process.
This work was funded through a Predoctoral Fellowship to the Harvard-Smithsonian Center for Astrophysics, a NASA Graduate Student Research Fellowship (NTG5-50233), and through a NSF grant (AST-9733367).
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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.