Stellar contents and star formation in the young open cluster Stock 8

TL;DR

This study characterizes the stellar population, star formation history, and initial mass function of the young open cluster Stock 8 using multi-wavelength photometry and spectroscopy, revealing non-coeval star formation and a break in the IMF.

Contribution

It provides detailed analysis of the cluster's properties, including age distribution, mass function slope, and spatially resolved star formation, which enhances understanding of star formation in young clusters.

Findings

Majority of YSOs are 1-5 Myr old, indicating ongoing star formation.

Mass function slope in the high-mass range matches Salpeter's value.

Younger YSOs are found in the Nebulous Stream and embedded cluster.

Abstract

We present $UBVI_c$ CCD photometry of the young open cluster Stock 8 with the aim to study the basic properties and star formation scenario in this region. The radius of the cluster is found to be $\sim 6^{\prime}$ ($\sim 3.6$ pc) and the reddening within the cluster region varies from $E(B-V)=0.40$ to 0.60 mag. The cluster is located at a distance of $2.05 \pm 0.10$ kpc. Using H$\alpha$ slitless spectroscopy and 2MASS NIR data we identified H$\alpha$ emission and NIR excess young stellar objects (YSOs), respectively. The colour-magnitude diagrams of these YSOs reveal that majority of these objects have ages between 1 to 5 Myr indicating a non-coeval star formation in the cluster. Massive stars in the cluster region reveal an average age of $\le$ 2 Myr. In the cluster region ($r \le 6^\prime$) the slope of the mass function (MF), $\Gamma$, in the mass range $\sim 1.0 \le M/M_\odot < 13.4$ can be represented by a power law having a slope of $-1.38\pm0.12$, which agrees well with Salpeter value (-1.35). In the mass range $0.3 \le M/M_\odot < 1.0$, the MF is also found to follow a power law with a shallower slope of $\Gamma = -0.58\pm 0.23$ indicating a break in the slope of the IMF at $\sim 1 M_\odot$. The slope of the $K$-band luminosity function for the cluster ($r \le 6^\prime$) is found to be $0.31\pm0.02$, which is smaller than the average value ($\sim$ 0.4) obtained for embedded star clusters. A significant number of YSOs are distributed along a Nebulous Stream towards the east side of the cluster. A small cluster is embedded in the Nebulous Stream. The YSOs lying in the Nebulous Stream and in the embedded cluster are found to be younger than the stars in the cluster Stock 8. It appears that star formation activity in the Nebulous Stream and embedded cluster may be independent from that of Stock 8.