New SPB stars in the field of the young open cluster NGC 2244 discovered by the MOST photometric satellite

TL;DR

This study reports the discovery of two new SPB stars in the young open cluster NGC 2244 using MOST satellite photometry, with frequency analysis suggesting they are likely pre-main-sequence stars, potentially the first known PMS SPB stars.

Contribution

The paper presents the first identification of candidate pre-main-sequence SPB stars in a young cluster, based on space-based photometry and frequency analysis.

Findings

Discovered two new SPB stars in NGC 2244.

Frequency analysis reveals g-mode oscillations consistent with PMS models.

Potential identification of the first known PMS SPB stars.

Abstract

During two weeks of nearly continuous optical photometry of the young open cluster NGC 2244 obtained by the MOST satellite, we discovered two new SPB stars, GSC 00154-00785 and GSC 00154-01871. We present frequency analyses of the MOST light curves of these stars, which reveal two oscillation frequencies (0.61 and 0.71 c/d) in GSC 00154-00785 and two (0.40 and 0.51 c/d) in GSC 00154-01871. These frequency ranges are consistent with g-modes of $\ell \leq 2$ excited in models of main-sequence or pre-main-sequence (PMS) stars of masses 4.5 - 5 $M_{\odot}$ and solar composition $(X, Z)= (0.7, 0.02)$. Published proper motion measurements and radial velocities are insufficient to establish unambiguously cluster membership for these two stars. However, the PMS models which fit best their eigenspectra have ages consistent with NGC 2244. If cluster membership can be confirmed, these would be the first known PMS SPB stars, and would open a new window on testing asteroseismically the interior structures of PMS stars.