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

Abstract

During two weeks of nearly continuous optical photometry of the young open cluster NGC 2244 obtained by the Microvariability and Oscillations of STars (MOST) satellite,we discovered two new slowly pulsating B (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 cycle d[superscript −1]) in GSC 00154−00785 and two (0.40 and 0.51 cycle d[superscript −1]) in GSC 00154−01871. These frequency ranges are consistent with g modes of l [less than or equal to] 2 excited in models of main-sequence or pre-main-sequence (PMS) stars of masses 4.5–5 M[subscript circled dot] 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.