Jeffries, R. D.

Contact Email: rdj@astro.keele.ac.uk
Institute: Keele University
First Coauthor: M. R. Thurston
Institute: University of Birmingham
Second Coauthor: N. C. Hambly
Institute: University of Edinburgh
Research URL:http://www.astro.keele.ac.uk/~rdj/
Subject Area: Star Clusters, Associations
Waveband: Optical
Technique: Photometry
Presentation: Poster Display
Title: The mass function and mass segregation in NGC 2516
Abstract: We present the results of a 0.86 square degree photometric survey of the open cluster NGC 2516, which has an age of 150Myr and may have a much lower metallicity than the similarly-aged Pleiades. We select 1254 low mass ( $0.2<M<2.0M_{\odot}$) cluster candidates, of which 70-80 percent are expected to be genuine. The mass function is metallicity dependent, but consistent with a Salpeter-like law ( $dN/d\log M\propto M^{-\alpha}$, $\alpha=+1.47\pm0.11$ or $\alpha=+1.67\pm 0.11$ for solar and half-solar metallicities) for $0.7<M<3.0M_{\odot}$. At lower masses ( $0.3<M<0.7M_{\odot}$) there is a sharp fall, with $\alpha=-0.75\pm0.20$ (solar metallicity) or $\alpha=-0.49\pm0.13$(half-solar metallicity), which is inconsistent with the flatter mass functions seen in the Pleiades and field populations. We explain this by showing mass segregation has been at work in NGC 2516 - more than half the low mass stars are expected to be outside our survey. The mass of NGC 2516 stars with $M>0.3M_{\odot}$ inside our survey is $950-1200M_{\odot}$. Correcting for mass segregation increases this to $\sim1240-1560M_{\odot}$, about twice that of the Pleiades.