On the Analysis of Two Low-Mass, Eclipsing Binary Systems in the Young Orion Nebula Cluster

Abstract

This thesis presents the analysis of two double-lined, detached, eclipsing binary systems associated with the young Orion Nebula Cluster, 2MASS J05352184–0546085 and Parenago 1802. We present a multi-band, multi-epoch analysis including both radial velocity and light curves to determine the eclipsing binaries' properties. The components of both systems have ages of ~ 1 Myrs and are found to be in the pre-main sequence (PMS) phase. They provide valuable observational constraints for the early stages of theoretical evolutionary models. The goal of this thesis is to precisely determine the physical properties of the components of two low-mass eclipsing binaries and to characterize their orbits.

Parenago 1802 is the lowest mass twin system known among PMS binaries. The eclipsing components have equal masses (~ 0.4 Msun) to within ~ 3 %. The components' radii are large as expected for PMS stars, but they differ by ~ 7 %. Their effective temperatures differ by ~ 9 %. We measure the photometric rotation period of the components from the periodic variability, and find that the components are not yet synchronized to their orbital motion. The small, but significant eccentricity (e = 0.0166 ± 0.003) of the orbit makes this system one of the shortest period (~ 4.674 d) PMS, close binaries known to be non-circular.

The eclipsing binary 2MASS J05352184–0546085 is the only known system composed of two substellar objects with masses below the hydrogen burning limit (M1 = 0.0572 ± 0.0033 and M2 = 0.0366 ± 0.0022 Msun). The components' radii are larger than those of older brown dwarfs of similar masses. The more massive brown dwarf is found to be rotating over four times faster and appears to be cooler than its companion. We find that surface spots, probably due to enhanced activity, may explain the observed apparent temperature reversal if they cover a large area (~ 65%) of the more massive component in a symmetric configuration.

In both cases, the theoretical models are able to reproduce some but not all of the systems' observed properties. These young, eclipsing systems thus underline the successful predictions in the low-mass regime of the current evolutionary models but also their limitations.