EDP Sciences
Free access
Issue
A&A
Volume 387, Number 2, May IV 2002
Page(s) 463 - 478
Section Stellar clusters and associations
DOI http://dx.doi.org/10.1051/0004-6361:20020380


A&A 387, 463-478 (2002)
DOI: 10.1051/0004-6361:20020380

ROSAT PSPC/HRI observations of the open cluster NGC 2422

M. Barbera1, F. Bocchino1, F. Damiani1, G. Micela1, S. Sciortino1, F. Favata2 and F. R. Harnden Jr.3

1  INAF - Osservatorio Astronomico di Palermo G.S. Vaiana, Piazza del Parlamento 1, 90134 Palermo, Italy
2  Astrophysics Division, Space Science Department of ESA, ESTEC, Postbus 299, 2200 AG Noordwijk, The Netherlands
3  Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge (MA), USA

(Received 15 January 2001 / Accepted 14 February 2002)

Abstract
We present the results of a ROSAT study of NGC 2422, a southern open cluster at a distance of about 470 pc, with an age close to the Pleiades. Source detection was performed on two observations, a 10-ks PSPC and a 40-ks HRI pointing, with a detection algorithm based on wavelet transforms, particularly suited to detecting faint sources in crowded fields. We have detected 78 sources, 13 of which were detected only with the HRI, and 37 detected only with the PSPC. For each source, we have computed the 0.2-2.0 keV X-ray flux. Using optical data from the literature and our own low-dispersion spectroscopic observations, we find candidate optical counterparts for 62 X-ray sources, with more than 80% of these counterparts being late type stars. We have assigned to the optical sources an astrometric and/or a photometric membership flag, depending on which data are available to us. The number of sources (38 of 62) with high membership probability counterparts is consistent with that expected for Galactic plane observations at our sensitivity. We have computed maximum likelihood X-ray luminosity functions (XLF) for F and early-G type stars with high membership probability. Heavy data censoring due to our limited sensitivity permits determination of only the high-luminosity tails of the XLFs; the distributions are indistinguishable from those of the nearly coeval Pleiades cluster.


Key words: open clusters and associations: individual: NGC 2422 -- stars: coronae -- X-rays: stars

Offprint request: M. Barbera, barbera@astropa.unipa.it

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© ESO 2002