Fundamental parameters of very low mass stars in eclipsing binary systems

Fitzpatrick, Ezri

Abstract

Photometry of binary star and extrasolar planet transits offer an opportunity to characterise their components and test stellar models. When investigating exoplanets, it is important properly understand the host star otherwise large systematic errors will be introduced. Radii predicted by models of low-mass and very low-mass are often too low when compared with observations. This discrepancy between theory and observation as called the “radius inflation problem”. In this thesis I investigate how well current stellar models of F/G stars predict the centre-to-limb variation (known as limb darkening) observed and whether the M dwarf companions show signs of the radius inflation problem. I use a class of eclipsing binary star with a low-mass companion (EBLM).
I fit a transit model with the Claret 4-parameter law to TESS light curves for 19 EBLMs to parameterise the limb darkening. I combined this with observations from Maxted (2023) for targets with transiting hot Jupiters in the Kepler and TESS bands and compared with limb darkening parameters predicted by PHOENIX−COND (Claret, 2018) and MPS−ATLAS (Kostogryz et al., 2022), testing for trends with effective temperature and metallicity. I found a significant linear trend in model vs observed limb darkening parameters with effective temperature for Kepler systems from limb darkening parameters predicted by PHOENIX-COND. For other model and band combinations, I find no such trends, only offsets between theory and observation, likely caused by magnetic activity. I suggest trends are seen in the Kepler band but not TESS due to line blanketing but further investigation is needed.
I calculate masses, radii, effective temperatures and gravities of the secondary star from fit parameters and compare with MIST isochrones. By interpolating over metallicity for models of 4 Gyr, I find an average radius inflation of 1.9 ± 1.0% over my sample. Hence, my observations agree well with MIST models.

Citation

Fitzpatrick, E. Fundamental parameters of very low mass stars in eclipsing binary systems. (Thesis). Keele University. Retrieved from https://keele-repository.worktribe.com/output/956373

• Thesis Type: Thesis
• Deposit Date: Oct 28, 2024
• Publicly Available Date: Oct 28, 2024
• Public URL: https://keele-repository.worktribe.com/output/956373
• Award Date: 2024-10