XMM-Newton survey of the low-metallicity open cluster NGC 2516

¹ Osservatorio Astronomico di Palermo G.S. Vaiana, Piazza del Parlamento 1, 90134 Palermo, Italy
² X-Ray Astronomy Group, Department of Physics and Astronomy, University of Leicester, Leicester, LE1 7RH, UK
³ Max-Plank-Institut für Extraterrestrische Physik, Giessenbachstraße, 85741 Garching bei München, Germany
⁴ European Space Research and Technology Center, 2200 AG Noordwijk ZH, The Netherlands
⁵ Department of Physics and Astronomy, Keele University, Staffordshire, ST5 5BG, UK

Corresponding author: S. Sciortino; sciorti@oapa.astropa.unipa.it

Received: 2 October 2000
Accepted: 4 November 2000

Abstract

We present the first results of an XMM-Newton EPIC survey of NGC 2516, a southern low-metallicity open cluster with an age close to the Pleiades. The attained limiting sensitivity is of ~2.4 10^-15 erg s^-1 cm^-2 in the 0.1-4.0 keV bandpass. This has been achieved by summing the data of the MOS and PN cameras of two distinct observations for a total exposure time of ~33 ks and by analyzing the summed data set with the wavelet detection algorithm developed at Osservatorio Astronomico di Palermo (OAPA) that has yielded over 200 X-ray detections. Using data just from a single exposure or from a single camera would have reduced by a factor 2-4 our limiting sensitivity and would have resulted in 25-40% less X-ray detections. To date, 129 detections have as counterparts one or more of the 540 photometrically selected cluster members in the surveyed region, for a total of 147 likely detected members, with unique identification in 112 cases. We derive the X-ray luminosity functions (XLF) of NGC 2516 members of different spectral types and compare them with those of the more metal rich, approximately coeval Pleiades cluster, finding the NGC 2516 photometrically selected dG and dK stars less luminous than the Pleiades. The XLFs of the NGC 2516 and of the Pleiades dM stars are indistinguishable. We compare the XMM-Newton results with those recently obtained with Chandra.