Cool Stars 14 - Submitted Abstract # 265
This version created on 05 October 2006

An Assessment of Empirical Constraints on the Ages and Age Spread of
Stars in Star Forming Regions and Young Clusters


Lynne Hillenbrand, Caltech
Amber Swenson, UCB
Russel White, UA-H

Pre-main sequence evolutionary theory is, in general, not
well-calibrated to observations.  With care, the observations can be
converted into effective temperature and luminosity (the
Hertzsprung-Russell diagram) which the theoretical calculations also
predict as a function of stellar mass and age.  For a sample of young
stellar clusters ranging in age from <1 Myr to >100  Myr, we have
tested the loci of luminosity as a function of effective temperature
against various predicted pre-main sequence isochrones.  As we found
in Hillenbrand & White (2004) which tested stellar masses, here for
the stellar ages, some evolutionary calculations fare better than
others in reproducing the empirical sequences, but systematic
differences between all pre-main sequence evolutionary calculations
and the data remain.  We also simulate from the evolutionary models
hypothetical clusters of varying star formation history and
multiplicity properties, and compare the resulting HR diagram
predictions to observed clusters.  This effort is directed at
assessing the apparent luminosity spreads in star forming regions and
young clusters, which are often erroneously interpreted as true
luminosity spreads corresponding to true age spreads.

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