Characterising young eclipsing binaries and their environments in NGC 2264

Stellar evolution models underpin much of astrophysics, yet they are severely under-constrained on the pre-main sequence. The masses, radii, temperatures and luminosities of detached double-lined eclipsing binaries (EBs) can be determined in a model-independent manner from the light and radial velocity curves of the system. When these reach a precision of a few percent or less, they provide one of the most powerful observational tests of stellar evolution theory. Furthermore, young binary star systems display significant photometric and spectroscopic variability over a range of timescales and wavelengths. EBs offer powerful test-beds for characterising such variability, as the stellar parameters and orbital geometry are known to high precision.
This thesis presents the characterisation of EBs discovered by the CoRoT and Spitzer space missions in the ∼3 Myr old NGC 2264 star forming region. A sample of EBs in a young open cluster such as this, constitutes a particularly strong test of stellar evolution models because the EBs share the same age and composition, yet span a wide range of masses.
We present the discovery of CoRoT 223992193, a detached, double-lined eclipsing binary, which comprises two pre-main sequence M-dwarfs and shows evidence of a circumbinary disk. We develop innovative approaches, based on Gaussian process regression, to determine the fundamental stellar parameters. At the time of discovery this was only the ninth pre-main sequence eclipsing binary (PMS EB) with component masses below 1.5 M⊙ and provides a useful test of stellar evolution models.
CoRoT 223992193 is the first low-mass PMS EB to show evidence of a circumbinary disk and displays significant photometric and spectroscopic variability. The two stars are found to possess slightly different rotation periods: the primary is consistent with synchronisation while the secondary rotates slightly supersynchronously. The photometric and spectroscopic variations are consistent with the picture of two active stars possibly undergoing non-steady, low-level accretion; the system’s very high inclination provides a new view of such variability.
The techniques developed in characterising CoRoT223992193 are applied to the NGC2264 EB sample. These work well for near equal-mass systems and two main sequence EBs are solved. However, primarily due to the one-dimensional nature of the radial velocity determination, the majority of the sample remains unsolved; more powerful methods are presented and are suggested for further work. Four low-mass EBs show evidence for youth, with three of these displaying low-to-extreme brightness (and hence mass) ratios. No such PMS systems have been reported in the literature. Once complete the full NGC 2264 sample will form one of the most stringent tests of PMS stellar evolution models to date.
Finally, we present a visual multiple containing three EBs spanning B–M spectral types. Two of these systems show evidence for youth and cluster membership; the third is more ambiguous. Further observations are required to confirm the nature of this multiple, but if all three EBs are constituent members, it would be the first triply-eclipsing multiple system discovered, and will provide a powerful test of star formation and stellar evolution models in dense cluster environments.