MOST satellite photometry of stars in the M67 field: Eclipsing binaries, blue stragglers and delta-Scuti variables

TL;DR

This study uses MOST satellite photometry to analyze variable stars in M67, revealing detailed light curves of eclipsing binaries, blue stragglers, and delta-Scuti variables, and discovering new binary systems with high precision.

Contribution

First detailed space-based photometry of variable stars in M67, including modeling of eclipsing binaries and discovery of new systems, with improved data quality over previous observations.

Findings

High-precision light curves of ES Cnc and EV Cnc

Discovery of two new long-period eclipsing binaries

Detection of multiple pulsation frequencies in delta-Scuti stars

Abstract

We present two series of MOST (Microvariability & Oscillations of STars) space-based photometry, covering nearly continuously 10 days in 2004 and 30 days in 2007, of selected variable stars in the upper Main Sequence of the old open cluster M67. New high-precision light curves were obtained for the blue-straggler binary/triple systems AH Cnc, ES Cnc and EV Cnc. The precision and phase coverage of ES Cnc and EV Cnc is by far superior to any previous observations. The light curve of ES Cnc is modelled in detail, assuming two dark photospheric spots and Roche geometry. An analysis of the light curve of AH Cnc indicates a low mass ratio (q about 0.13) and a high inclination angle for this system. Two new long-period eclipsing binaries, GSC 814-323 and HD75638 (non-members of M67) were discovered. We also present ground-based DDO spectroscopy of ES Cnc and of the newly found eclipsing binaries. Especially interesting is HD75638, a member of a visual binary, which must itself be a triple or a higher-multiplicity system. New light curves of two delta Scuti pulsators, EX Cnc and EW Cnc, have been analyzed leading to detection of 26 and 8 pulsation frequencies of high temporal stability.