Photometric variability of the pre-main sequence stars towards the Sh 2-190 region

TL;DR

This study investigates the photometric variability of pre-main sequence stars in the Sh 2-190 region, revealing correlations between disc presence, rotation, and variability, with implications for star formation and evolution.

Contribution

It provides new insights into the variability patterns of PMS stars, linking disc properties to rotation and brightness variations, based on extensive time-series photometry.

Findings

Stars with thicker discs rotate slower and show larger variability.

Variability in Class II sources is mainly due to thick discs, while in Class III it's due to cool spots.

X-ray activity is at saturation level, less influenced by discs in younger PMS stars.

Abstract

We present the results from our time-series imaging data taken with the 1.3m Devasthal fast optical telescope and 0.81m Tenagara telescope in $V$, $R_{c}$, $I_{c}$ bands covering an area of $\sim18^\prime.4\times 18^\prime.4$ towards the star-forming region Sh 2-190. This photometric data helped us to explore the nature of the variability of pre-main sequence (PMS) stars. We have identified 85 PMS variables, i.e., 37 Class II and 48 Class III sources. Forty-five of the PMS variables are showing periodicity in their light curves. We show that the stars with thicker discs and envelopes rotate slower and exhibit larger photometric variations compared to their disc-less counterparts. This result suggests that rotation of the PMS stars is regulated by the presence of circumstellar discs. We also found that the period of the stars show a decreasing trend with increasing mass in the range of $\sim$0.5-2.5 M$_\odot$. Our result indicates that most of the variability in Class II sources is ascribed to the presence of thick disc, while the presence of cool spots on the stellar surface causes the brightness variation in Class III sources. X-ray activities in the PMS stars were found to be at the saturation level reported for the main sequence (MS) stars. The younger counterparts of the PMS variables are showing less X-ray activity hinting towards a less significant role of a stellar disc in X-ray generation.