Deep V and I CCD photometry of young star cluster NGC 1893 with the 3.6m DOT

Abstract

Young star clusters consisting of massive stars are the ideal sites to study the star formation processes and influence of massive stars on the subsequent star formation. NGC 1893 is a young star cluster associated with the Hii region Sh2-236. It contains about five ‘O’-type stars and several early ‘B’-type stars. It is located at a moderate distance of $\sim$3.25 kpc and has a reddening, $E(B-V) \sim 0.4$ mag. To characterize the young low-mass stellar population in the central portion of the cluster, we carried out deep VI band observations of the region using the $4\mathrm{K} \times 4$K CCD IMAGER mounted on the 3.6-m Devasthal Optical Telescope. Our analysis shows that the present data are deep enough to detect stars below $V\sim 24$ mag. We found optical counterparts of $\sim$220 candidates, including young stars and unclassified cluster members from Caramazza et al. (2008). We estimated the membership probabilities of the Gaia sources (mostly bright stars with $G<19$ mag) located within the cluster radius using the Gaia EDR3. Toward the fainter end, we used the optical color-magnitude diagram (CMD) to select the cluster members from a sample of young stars. The locations of young stars on the CMD show that a majority of them are low-mass stars with age <10 Myr. The unclassified candidates and X-ray sources from Caramazza et al. (2012) are also found to be young low-mass stars. In total, we identified $\sim$425 young stars with age <10 Myr, and 110 of these are new. Most of these stars appear as kinematic members of the cluster. By examining the CMD for the stars in the cluster region, we suggest that the cluster has insignificant contamination due to field stars in the pre-main-sequence zone of the CMD. The slope of the mass function in the mass range $0.2\le M/M_\odot \le 2.5$ is found to be $\Gamma = -\,1.43 \pm 0.15$, consistent with those of other star-forming complexes. The spatial distribution of the young stars as a function of mass suggests that toward the cluster center, most of the stars are massive.