The stellar contents and star formation in the NGC 7538 region
  Deep optical photometric data on the NGC 7538 region were collected and
combined with archival data sets from $Chandra$, 2MASS and {\it Spitzer}
surveys in order to generate a new catalog of young stellar objects (YSOs)
including those not showing IR excess emission. This new catalog is complete
down to 0.8 M$_\odot$. The nature of the YSOs associated with the NGC 7538
region and their spatial distribution are used to study the star formation
process and the resultant mass function (MF) in the region. Out of the 419
YSOs, $\sim$91\% have ages between 0.1 to 2.5 Myr and $\sim$86\% have masses
between 0.5 to 3.5 M$_\odot$, as derived by spectral energy distribution
fitting analysis. Around 24\%, 62\% and 2\% of these YSOs are classified to be
the Class I, Class II and Class III sources, respectively. The X-ray activity
in the Class I, Class II and Class III objects is not significantly different
from each other. This result implies that the enhanced X-ray surface flux due
to the increase in the rotation rate may be compensated by the decrease in the
stellar surface area during the pre-main sequence evolution. Our analysis shows
that the O3V type high mass star `IRS 6' might have triggered the formation of
young low mass stars up to a radial distance of 3 pc. The MF shows a turn-off
at around 1.5 M$_\odot$ and the value of its slope `$\Gamma$' in the mass range
$1.5 <$M/M$_\odot < 6$ comes out to be $-1.76\pm0.24$, which is steeper than
the Salpeter value.
