POSTER PAPER 4.08
The Mass Function and Mass Segregation in NGC 2516
R. D. Jeffries, M. R. Thurston, N. C. Hambly
Institute: Department of Physics, Keele University, UK
Institute: School of Physics and Astronomy, University of
Birmingham, UK
Institute: Institute for Astronomy, Edinburgh, UK
Contact Email: rdj@astro.keele.ac.uk
Abstract:
We present the results of a 0.86 square degree BVIc survey of
the open cluster NGC 2516, which has an age of 150 Myr and may have a
much lower metallicity than the similarly-aged Pleiades. We select 1254
low mass (0.2 < M < 2.0 MSun) cluster candidates, of which 70--80
percent are expected to be genuine. We find that 26 +/- 5 percent of A
to M-type stars in the cluster are binaries with mass ratio q > 0.6, in
good agreement with the Pleiades. The mass function is slightly model
and metallicity dependent, but consistent with a Salpeter-like law
(dN/dlogM proportional to M-a with
a = +1.6 +/- 0.2 for
0.7 < M < 3.0 MSun . At lower masses (
0.3 < M < 0.7 MSun)
there is a sharp fall, with a = -0.75 +/- 0.25,
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 of cluster stars with M < 0.6 MSun
are expected to be outside our
surveyed area. The mass of NGC 2516 stars with M > 0.3 MSun inside our
survey is 1000 MSun . Correcting for mass segregation and binarity
increases this to ~ 1400 MSun , about twice that of the
Pleiades.
Index Keywords: Open Clusters; Mass Function; Mass Segregation; Low-mass Stars
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Manuscript submitted: 2001-Aug-30
"The Future of Cool-Star Astrophysics", 2003, Eds. A. Brown,
G. M. Harper, & T. R. Ayres.
Proceedings of 12th Cambridge Workshop on Cool Stars, Stellar Systems,
& The Sun,
© 2003 University of Colorado.