Abstract
ABSTRACT The accuracy of theoretical mass, radius, and effective temperature values for M-dwarf stars is an active topic of debate. Differences between observed and theoretical values have raised the possibility that current theoretical stellar structure and evolution models are inaccurate towards the low-mass end of the main sequence. To explore this issue, we use the CHEOPS satellite to obtain high-precision light curves of eclipsing binaries with low-mass stellar companions. We use these light curves combined with the spectroscopic orbit for the solar-type companion to measure the mass, radius, and effective temperature of the M-dwarf star. Here, we present the analysis of three eclipsing binaries. We use the pycheops data analysis software to fit the observed transit and eclipse events of each system. Two of our systems were also observed by the TESS satellite – we similarly analyse these light curves for comparison. We find consistent results between CHEOPS and TESS, presenting three stellar radii and two stellar effective temperature values of low-mass stellar objects. These initial results from our on-going observing programme with CHEOPS show that we can expect to have ∼24 new mass, radius, and effective temperature measurements for very low-mass stars within the next few years.
Highlights
Understanding the host star is one of the most crucial parts of exoplanet characterization
We found that the predicted time of superior conjunction for our fitted model parameters is outside the duration of our scheduled CHEOPS visit
We do not yet have effective temperature measurements for these Mdwarfs, but the methods we have developed here can be applied to the CHEOPS and TESS light curves for those stars, as well as other EBLM binaries observed by these instruments, to provide a more complete picture for these systems
Summary
Understanding the host star is one of the most crucial parts of exoplanet characterization. Any uncertainty in these models leads to systematic errors in the inferred stellar and exoplanetary properties This has become a potential issue regarding low-mass star systems’ recent popularity as targets for exoplanet observation (Charbonneau & Deming 2007; Quirrenbach et al 2014; Gillon et al 2017; Delrez et al 2018). Hundreds of eclipsing binaries with low-mass companions have been identified using data from the WASP project (Pollacco et al 2006), and we have measured the spectroscopic orbits for the primary stars in more than 100 of these EBLM systems (Triaud et al 2017). A number of studies have reported inconsistencies between the observed radii and M-dwarfs and theoretically predicted radii from models of low-mass stars, an effect commonly called radius inflation A much larger sample of precise and accurate mass, radius, and effective measurements for M-dwarfs of known metallicity is needed so that we can reliably estimate the properties of low-mass host stars in planetary systems.
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