Charles J. Lada
Harvard-Smithsonian Center for Astrophysics
and
Elizabeth A. Lada
Stellar clusters are born embedded within giant molecular clouds (GMCs) and
during their formation and early evolution are often only visible at infrared
wavelengths, being heavily obscured by dust. Over the last 15 years advances
in infrared detection capabilities have enabled the first systematic studies
of embedded clusters in galactic molecular clouds. In this article we review
the current state of empirical knowledge concerning these extremely young
protocluster systems. From a survey of the literature we compile the first
extensive catalog of galactic embedded cluster properties. We use the
catalog to construct the mass function and estimate the birthrate for
embedded clusters within roughly 2 kpc of the Sun.
We find that the embedded cluster birthrate exceeds
that of visible open clusters by an order of magnitude or more indicating a
high infant mortality rate for protocluster systems. Less than 4-7% of
embedded clusters survive emergence from molecular clouds to become bound
clusters of Pleiades age. The vast majority (90%) of stars that form in embedded
clusters form in rich clusters of 100 or more members with masses in excess of
50 solar masses. Moreover, observations of nearby cloud complexes indicate that
embedded clusters account for a significant (70-90%) fraction of all stars
formed in GMCs. We review the role of embedded clusters in investigating
the nature of the IMF which, in one nearby example, has been measured over
the entire range of stellar and substellar mass, from OB stars to subsellar
objects near the deuterium burning limit. We also review the role embedded
clusters play in the investigation of circumstellar disk evolution and the
important constraints they provide for understanding the origin of planetary systems.
Finally, we discuss current ideas concerning the origin and dynamical evolution
of embedded clusters and the implications for the formation of bound open clusters.
Annual Reviews of Astronomy and Astrophysics Vol. 41, 2003, in press
If there are problems please mail me
clada@cfa.harvard.edu
.
Astronomy Department, University of Florida
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