The Low Mass IMF of Young Open Clusters

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Session 91 -- Young Stars and Young Clusters
Oral presentation, Wednesday, 11, 1995, 10:00am - 11:30am

[91.07D] The Low Mass IMF of Young Open Clusters

D.~M.~Williams, G.~H.~Rieke, M.~J.~Rieke (Steward Observatory), J.~R.~Stauffer (CfA), F.~Comer\'on (Universitat de Barcelona)

We present results of our study of the IMF of young open clusters, using a number of different techniques. The clusters studied have a range of ages, from $\sim 10^{6}$ to $\sim 10^{9}$ yr. Infrared spectroscopy (2.2 $\mu$m) has been obtained for a brown dwarf candidate and other VLM stars in the embedded cluster $\rho$ Ophiuchi. The spectra of the Ophiuchi sources are compared with those of M dwarfs to identify features which characterize cool stellar atmospheres in the embedded sources. For the non-embedded clusters Praesepe and the Pleiades, we have obtained V, I, and K band photometry. The photometry reliably reaches $0.08 M_{\sun}$ in Praesepe and $0.05 M_{\sun}$ in the Pleiades. We show that the V, V-K color-magnitude diagram provides a very efficient membership criterion, much better than either I, I-K, or V, V-I. The mass function we derive for Praesepe is similar to the field star IMF. We conclude that dynamical processes that can lead to evaporation of low mass members from stellar clusters have not occurred to a substantial extent in Praesepe and therefore will be negligible in the Pleiades. Our photometric survey of the Pleiades allows us to derive the IMF in the cluster down to $\sim 0.05M_{\sun}$.

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