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I. Platais (Johns Hopkins U.), C. Melo (ESO), J.-C. Mermilliod (LAstro/EPFL, Switzerland), V. Kozhurina-Platais (STScI), J. P. Fulbright (Johns Hopkins U.), R. Mendez, M. Altmann (U. de Chile), J. Sperauskas (Vilnius U., Lithuania), WOCS Collaboration
The nearby young open cluster IC 2391 in Vela is sparse, containing only ~50 members down to 0.5 M_sun. Until recently the major source of cluster membership was from X-ray imaging by ROSAT and XMM over a relatively small area of the sky. This study considers a 6 times larger area, or ~9 deg2. We have obtained new proper motions for 6991 stars down to V~15. The precision of proper motions (\sigma=1.7 mas yr-1) in combination with the cluster's relatively fast motion across the sky allow us to obtain reliable membership probabilities. We also obtained precise radial velocity measurements with Coravel and FEROS for 76 probable members. In addition, new BV CCD photometry was obtained for the majority of probable cluster members. A total of 19 new cluster members, confirmed by proper motion, radial velocity, photometry and Li abundance, fill in the F2-K1 spectral range, crucial to the main sequence fitting. By adding the previously known probable members, also confirmed by all of the above criteria with the exception of Li abundance, we have established a sample of 59 bona fide cluster members down to 0.5 M_sun. The main sequence fitting yields a 0.1 mag larger distance modulus than that derived from Hipparcos parallaxes. The high dispersion FEROS spectra (R~50,000) enabled the measurement of projected rotational velocities, metallicity, and Li abundance. The Li abundance pattern is similar to the earlier findings by Randich et al., typical for a 35 Myr old open cluster.
This study is supported in part by NSF grant AST 04-06689 to The Johns Hopkins University and the Taiwan-Baltic collaboration.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.