Photometric monitoring of open clusters: Low-mass eclipsing binary stars and the stellar mass-luminosity-radius relation

This thesis describes a photometric monitoring survey of Galactic star clusters designed to detect low-mass eclipsing binary star systems through variations in their relative lightcurves. The aim is to use cluster eclipsing binaries to measure the masses and radii of M-dwarf stars with ages and metallicities known from studies of brighter cluster stars. This information will provide an improved calibration of the mass-luminosity-radius relation for low-mass stars, be used to test stellar structure and evolution models, and help quantify the contribution of low-mass stars to the global mass census in the Galaxy.; The survey is designed to detect eclipse events in stars of ≲ 0.3 M⊙ and consists of 600 Gbytes of raw imaging data on six open clusters with a range of ages (∼ 0.15-4 Gyr) and metallicites (∼ -0.2-0.0 dex). The clusters NGC 1647 and M 35 contain excellent candidate systems showing eclipse like variations in brightness and photometry consistent with cluster membership. The analysis of these clusters and the eclipsing M-dwarf stars detected in them are presented.; Analysis of the candidate system in NGC 1647 confirms the object as a newly discovered M-dwarf eclipsing binary in the cluster with compenent masses of M1 = 0.47 +/- 0.05 M⊙ and M2 = 0.19 +/- 0.02 M⊙ . The small mass ratio (M2/M 1) and low secondary mass of this object provide an unprecedented opportunity to test stellar models. We find that no stellar evolution models are consistent with all the properties of both M-dwarf stars in the eclipsing binary.; The candidate in M 35 has been confirmed as an M-dwarf eclipsing binary, and the masses of the individual components are estimated to be M 1 ∼ 0.25 M⊙ and M2 ∼ 0.15 M⊙ . Additional high resolution spectroscopic and photometric observations, for which we have applied and been awarded time, are necessary to accurately derive the intrinsic properties of the individual stellar components. The completion of our analysis will yield values for the intrinsic properties of four M-dwarf stars of known age and metallicity with masses of ∼ 0.5-0.1 M⊙ .