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NGC2516XMM - NGC 2516 Cluster XMM-Newton X-Ray Point Source Catalog



This table contains the results from a deep X-ray survey of the young (~ 140 Myr), rich open cluster NGC 2516 obtained with the EPIC camera on board the XMM-Newton satellite. By combining the data from six observations, a high sensitivity, greater than a factor of 5 with respect to recent Chandra observations, has been achieved. Kaplan-Meier estimators of the cumulative X-ray luminosity distribution, statistically corrected for non-member contaminants, were built by the authors and compared to those of the nearly coeval Pleiades cluster. 431 X-ray sources were detected, and 234 of them have as optical counterparts cluster stars spanning the entire NGC 2516 main sequence. On the basis of X-ray emission and optical photometry, 20 new candidate members of the cluster have been identified; at the same time there are 49 X-ray sources without known optical or infrared counterpart. The X-ray luminosities of cluster stars span the range log L_x (erg s^-1) = 28.4 - 30.8. The representative coronal temperatures span the 0.3 - 0.6 keV (3.5 - 8 MK) range for the cool component and 1.0 - 2.0 keV (12 - 23 MK) for the hot one; similar values were found in other young open clusters like the Pleiades, IC 2391, and Blanco 1. While no significant differences were found in their X-ray spectra, NGC 2516 solar-type stars are definitely less luminous in X-rays than their nearly coeval Pleiades counterparts. The comparison with a previous ROSAT survey reveals the lack of variability amplitudes larger than a factor of 2 in solar-type cluster stars in a ~ 11 yr time scale, and thus activity cycles like in the Sun are probably absent or have a different period and amplitude in young stars.

NGC 2516 has been observed several times with XMM-Newton during the first two years of satellite operations for calibration purposes. The observations used in this analysis span a period of 19 months with exposure times between 10 and 20 ks. All of these observations have been performed with the thick filter. In the combined EPIC datasets the authors detected 431 X-ray sources with a significance level greater than 5.0 sigma, which should lead statistically to at most one spurious source in the field of view.

Catalog Bibcode



Deep X-ray survey of the young open cluster NGC 2516 with XMM-Newton.
    Pillitteri I., Micela G., Damiani F., Sciortino S.
   <Astron. Astrophys., 450, 993-1004 (2006)>


This table was created by the HEASARC in May 2007 based on CDS catalog J/A+A/450/993 files tablea1.dat and tableb1.dat.

HEASARC Implementation

In this HEASARC table, the table of 431 X-ray sources (Table A.1 in the reference paper) has been combined with the list of 239 cluster star counterparts (Table B.1 in the reference paper). Since there are 2 possible counterparts for 5 of the X-ray sources, we have listed these 5 X-ray sources twice, once for each optical counterpart, and thus there are (431 + 5) = 436 entries in this HEASARC table.


A running source number in order of increasing J2000.0 Declination, i.e., source number 1 is the furthest south, which uniquely identifies the X-ray source.

The name of the X-ray source using the '[PMD2006]' prefix (for Pillitteri, Micela, Damiani 2006), together with the X-ray source number, as recommended by the CDS Dictionary of Nomenclature of Celestial Objects.

The Right Ascension of the X-ray source in the selected equinox. This was given in J2000.0 coordinates to a precision of 0.01 seconds of time in the original table.

The Declination of the X-ray source in the selected equinox. This was given in J2000.0 coordinates to a precision of 0.01 arcseconds in the original table.

The Galactic Longitude of the X-ray source.

The Galactic Latitude of the X-ray source.

The count rate of the X-ray source, in MOS1-equivalent counts per second, as described in Section 2 of the reference paper.

The RMS uncertainty in the X-ray source count rate, in MOS1-equivalent counts per second.

The detection significance of the X-ray source, in units of the background mean standard deviation.

The exposure time, in seconds, that was used to calculate the count rate of the X-ray source, as obtained from the exposure maps, and thus taking into account any spatial non-uniformities due to vignetting, RGS grating obscuration, chip geometry etc.

The off-axis distance of the X-ray source, in arcminutes (presumably from the center of the combined EPIC X-ray image shown in Figure 1 of the reference paper).

A few X-ray sources do not have counterparts in optical or infrared bands. After having searched for optical counterparts of the X-ray sources in GSC-II, 2MASS and DENIS and the complete catalog of Jeffries et al. (2001, A&A, 375, 863), 49 sources were left without optical/infrared known counterparts, and have been marked with a 'U' for their source_flag value.

The identification number of the optical counterpart to the X-ray source, from an optical catalog built from the list of Jeffries et al. (2001, A&A, 375, 863), and (for 42 cluster stars brighter than V = 9.7) from Dachs and Kabus (1989, A&AS, 78, 25), referred to as the JTH number in the reference paper. The authors matched the positions of X-ray sources with the optical coordinates in the composite catalog. No significant systematic offsets were found between optical and X-ray astrometry. By studying the distribution of the offsets of matched sources, they chose a maximum identification radius of 7 arcseconds, where the number of observed matches is similar to the number of expected chance identifications.

The matching distance between the X-ray source and its proposed optical counterpart, in arcseconds. Five X-ray sources were doubly matched with close pairs in the optical catalog and are thus listed twice, once for each possible optical counterpart.

The V magnitude of the optical counterpart to the X-ray source.

The B-V color index of the optical counterpart to the X-ray source.

The V-I color index of the optical counterpart to the X-ray source.

The X-ray flux in the 0.3 - 7.9 keV band, in erg/s/cm^2. The authors have estimated a conversion factor (CF) in the 0.3 - 7.9 keV band between count rates (in units of the MOS 1 instrument, as obtained by the detection code) and their unabsorbed fluxes, derived by the spectral analysis of the bright X-ray sources of the cluster (see Sect. 2.3 of the reference paper); the resulting CF, used for all the cluster X-ray sources, was 9.5 x 10^{-12 erg cnt^-1 cm^-2. The 3-sigma uncertainty in the CF takes into account the dependence on the spectrum hardness and is +/- 14%; it would systematically shift fluxes and luminosities by +0.06 and -0.07 dex, respectively.

The RMS uncertainty in the X-ray flux in the 0.3 - 7.9 keV band, in erg/s/cm^2.

The logarithm of the X-ray luminosity in the 0.3 - 7.9 keV band, in erg/s, calculated from the X-ray flux assuming a distance to the cluster of 387 pc, as adopted by Jeffries et al. (1997) and Damiani et al. (2003). This distance is slightly larger than the Hipparcos satellite estimate of 346 pc; assuming this latter value, the luminosities would decrease by -0.05 dex.

The negative error in the logarithm of the X-ray luminosity in the 0.3 - 7.9 keV band in erg/s.

The positive error in the logarithm of the X-ray luminosity in the 0.3 - 7.9 keV band in erg/s.

The logarithm of the bolometric luminosity of the optical counterpart to the X-ray source, in erg/s.

The bolometric-to-X-ray luminosity ratio of the source.

Contact Person

Questions regarding the NGC2516XMM database table can be addressed to the HEASARC User Hotline.

Page Author: Browse Software Development Team
Last Modified: 10-May-2007