X-ray observations of eight young open star clusters: I. Membership and X-ray luminosity

Bhatt, Himali ; Pandey, J. C. ; Singh, K. P. ; Sagar, Ram ; Kumar, Brijesh (2013) X-ray observations of eight young open star clusters: I. Membership and X-ray luminosity Journal of Astrophysics and Astronomy, 34 (4). pp. 393-429. ISSN 0250-6335

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Official URL: http://www.ias.ac.in/jaa/dec2013/jaa-d-13-00059.pd...

Related URL: http://dx.doi.org/10.1007/s12036-013-9190-8


We present a detailed investigation of X-ray source contents of eight young open clusters with ages between 4 to 46 Myr using archival X-ray data from XMM-Newton. The probable cluster memberships of the X-ray sources have been established on the basis of multi-wavelength archival data, and samples of 152 pre-main sequence (PMS) low mass (<2M ⊙), 36 intermediate mass (2–10M ⊙) and 16 massive (>10M ⊙) stars have been generated. X-ray spectral analyses of high mass stars reveal the presence of high temperature plasma with temperature <2 keV, and mean L X/L bol of 10 − 6.9. In the case of PMS low mass stars, the plasma temperatures have been found to be in the range of 0.2 keV to 3 keV with a median value of ~1.3 keV, with no significant difference in plasma temperatures during their evolution from 4 to 46 Myr. The X-ray luminosity distributions of the PMS low mass stars have been found to be similar in the young star clusters under study. This may suggest a nearly uniform X-ray activity in the PMS low mass stars of ages ~4–14 Myr. These observed values of L X/L bol are found to have a mean value of 10− 3.6±0.4, which is below the X-ray saturation level. The LX/Lbol values for the PMS low mass stars are well correlated with their bolometric luminosities, that implies its dependence on the internal structure of the low mass stars. The difference between the X-ray luminosity distributions of the intermediate mass stars and the PMS low mass stars has not been found to be statistically significant. Their LX/Lbol values, however have been found to be significantly different from each other with a confidence level greater than 99.999% and the strength of X-ray activity in the intermediate mass stars is found to be lower compared to the low mass stars. However, the possibility of X-ray emission from the intermediate mass stars due to a low mass star in close proximity of the intermediate mass star can not be ruled out.

Item Type:Article
Source:Copyright of this article belongs to Indian Academy of Sciences.
Keywords:Open Clusters and Associations: NGC 663, NGC 869, NGC 884, NGC 7380, Berkeley 86, IC 2602, Trumpler 18, Hogg15; Stars: Pre-main Sequence; X-rays: Massive Stars, Intermediate Mass Stars, Low Mass Stars
ID Code:98433
Deposited On:11 Jul 2014 12:05
Last Modified:19 May 2016 10:26

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