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Astron. Astrophys. 357, 909-919 (2000)

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Rosat HRI observations of the open cluster NGC 2516

G. Micela 1, S. Sciortino 1, R.D. Jeffries 2, M.R. Thurston 3 and F. Favata 4

1 Osservatorio Astronomico di Palermo, Palazzo dei Normanni, 90134 Palermo, Italy (gmicela,ssciortino@oapa.astropa.unipa.it)
2 Department of Physics, Keele University, Keele, Staffordshire, ST5 5BG, UK (rdj@astro.keele.ac.uk)
3 School of Physics and Astronomy, University of Birmingham, Birmingham, B15 2TT, UK (mrthurston@clara.co.uk)
4 Astrophysics Division - Space Science Department of ESA, ESTEC, Postbus 299, 2200 AG Noordwijk, The Netherlands (ffavata@astro.estec.esa.nl)

Received 28 January 2000 / Accepted 14 March 2000


We present ROSAT HRI observations of the NGC 2516, a young southern open cluster with low metallicity. We detect 73 X-ray sources already detected with the PSPC and 12 new X-ray sources. The higher HRI spatial resolution allows us to improve the position of the previous known sources, and to better determine the optical counterparts of X-ray sources with respect to the PSPC data.

We find 28 sources with no catalogued counterparts, most with faint objects within their X-ray positional error circle. Multiband CCD photometry of these possible counterparts shows that about half of them are consistent with being dK and dM cluster members. Assuming that they are true NGC 2516 members, the derived X-ray luminosity is consistent with that observed in dK and dM stars in more metal-rich open clusters of similar age, suggesting that the activity level at which X-ray saturation occurs is insensitive to a change of a factor two in stellar metallicity.

Key words: Galaxy: open clusters and associations: individual: NGC 2516 – stars: coronae – X-rays: stars

Send offprint requests to: G. Micela

© European Southern Observatory (ESO) 2000

Online publication: June 5, 2000