X-ray observations of eight young open star clusters : I. Membership and
  X-ray Luminosity
  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 (< 2 M_\odot), 36 intermediate mass (2 - 10
M_\odot) and 16 massive (> 10 M_\odot) 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\pm0.4}, which is below the X-ray saturation level.The L_X/L_{bol}
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 L_X/L_{bol} values, however have been found to
be significantly different from each other with a confidence level greater than
99.999%. 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 due to the limited spatial resolution of XMM-Newton.
