* Astronomy

Title: The stellar contents and star formation in the NGC 7538 region
Author: Saurabh Sharma, A. K. Pandey, D. K. Ojha, Himali Bhatt, K. Ogura, N. Kobayashi, R. Yadav, J. C. Pandey

Deep optical photometric data on the NGC 7538 region were collected and combined with archival data sets from Chandra, 2MASS and Spitzer surveys in order to generate a new catalogue of young stellar objects (YSOs) including those not showing IR excess emission. This new catalogue is complete down to 0.8 solar masses. 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, ~91% have ages between 0.1 to 2.5 Myr and ~86% have masses between 0.5 to 3.5 solar masses, 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 solar masses and the value of its slope 'Gamma' in the mass range 1.5<M/solar masses<6 comes out to be -1.76±0.24, which is steeper than the Salpeter value.

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