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Description
This table provides a list of X-ray sources detected in a ~50 ks XMM-Newton X-ray observation of the open cluster NGC 752. For the sources with 2MASS counterparts, the values of their magnitudes in the J, H and K bands are also given. Additionally, for the sources with a Chandra counterpart (within a search radius of 5 arcsec), the values of their Chandra source number (as given in the related Browse table NGC752CXO) are also given. Very little is known about the evolution of stellar activity between the ages of the Hyades (0.8 Gyr) and the Sun (4.6 Gyr). To gain information on the typical level of coronal activity at a star's intermediate age, the authors have studied the X-ray emission from stars in the 1.9 Gyr-old open cluster NGC 752. They analyzed a ~ 140 ks Chandra observation of NGC 752 and a ~50 ks XMM-Newton observation of the same cluster. They detected 262 X-ray sources in the Chandra data and 145 sources in the XMM-Newton observation. Around 90% of the catalogued cluster members within Chandra's field of view are detected in the X-ray observation. The X-ray luminosity of all observed cluster members (28 stars) and of 11 cluster member candidates was derived. These data indicate that, at an age of 1.9 Gyr, the typical X-ray luminosity L<sub>x</sub> of the cluster members with masses of 0.8 to 1.2 solar masses is 1.3 x 10<sup>28</sup> erg s<sup>-1</sup>, which is approximately a factor of 6 times less intense than that observed in the younger Hyades. Given that L<sub>x</sub> is proportional to the square of a star's rotational rate, the median L<sub>x</sub> of NGC 752 is consistent, for t >= 1 Gyr, with a decaying rate in rotational velocities v<sub>rot</sub> ~ t<sup>-alpha</sup> with alpha ~ 0.75, steeper than the Skumanich relation (alpha ~ 0.5) and significantly steeper than that observed between the Pleiades and the Hyades (where alpha <0.3), suggesting that a change in the rotational regimes of the stellar interiors is taking place at an age of ~ 1 Gyr. NGC 752 was observed for 49 ks by the XMM-Newton EPIC camera on February 5, 2003 starting at 23:29:25 UT, and the nominal pointing was towards J2000.0 RA and Declination of (01:57:38, +37:47:60), thus the XMM-Newton field-of-view (FOV) includes the Chandra FOV. For the source detection, the authors used the PWXDETECT code developed at Palermo Observatory and derived from the analogous Chandra PWDETECT code based on wavelet transform analysis. This allows the three EPIC exposures (PN, MOS1 and MOS2) to be combined in order to gain a deeper sensitivity with respect to the source detection based on single images. There were 145 point sources detected in the energy band 0.5 - 2.0 keV. An extended source (not listed in this present table), very likely a galaxy cluster, is also visible in the EPIC data. The authors searched for 2MASS counterparts to the XMM-Newton sources using a search radius of 5 arcsec and found a counterpart for 38 sources. As for the Chandra data, all sources with a visible counterpart from DLM94 have also a 2MASS counterpart, so this leaves 15 XMM-Newton sources with a 2MASS counterpart and no counterpart in Daniel et al. (1994, PASP, 106, 281); of these, 3 were also detected by Chandra; of the other 12, 10 are outside the Chandra FOV, while two are within it (XMM-Newton sources 58 and 65). Source 65 was caught by XMM-Newton during the decay phase of a flare, which explains why it is not detected in the Chandra data. For source 58 there is no immediate explanation for this, since the light curve does not show evidence of a flare. No additional near-IR counterpart to the XMM-Newton sources was found within the Point Source Reject Table of the 2MASS Extended Mission. This table was created by the HEASARC in October 2008 based on the electronic version of Table 7 from the reference paper which was obtained from the CDS website, i.e., their catalog J/A+A/490/113 file table7.dat. This is a service provided by NASA HEASARC .
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