The EBLM project

Abstract

Some M-dwarfs around F-/G-type stars have been measured to be hotter and larger than predicted by stellar evolution models. Inconsistencies between observations and models need to be addressed with more mass, radius, and luminosity measurements of low-mass stars to test and refine evolutionary models. Our aim is to measure the masses, radii and ages of the stars in five low-mass eclipsing binary systems discovered by the WASP survey. We used WASP photometry to establish eclipse-time ephemerides and to obtain initial estimates for the transit depth and width. Radial velocity measurements were simultaneously fitted with follow-up photometry to find the best-fitting orbital solution. This solution was combined with measurements of atmospheric parameters to interpolate evolutionary models and estimate the mass of the primary star, and the mass and radius of the M-dwarf companion. We assess how the best fitting orbital solution changes if an alternative limb-darkening law is used and quantify the systematic effects of unresolved companions. We also gauge how the best-fitting evolutionary model changes if different values are used for the mixing length parameter and helium enhancement. We report the mass and radius of five M-dwarfs and find little evidence of inflation with respect to evolutionary models. The primary stars in two systems are near the “blue hook” stage of their post sequence evolution, resulting in two possible solutions for mass and age. We find that choices in helium enhancement and mixing-length parameter can introduce an additional 3−5% uncertainty in measured M-dwarf mass. Unresolved companions can introduce an additional 3−8% uncertainty in the radius of an M-dwarf, while the choice of limb-darkening law can introduce up to an additional 2% uncertainty. The choices in orbital fitting and evolutionary models can introduce significant uncertainties in measurements of physical properties of such systems.

A long-period (P = 61.8 d) M5V dwarf eclipsing a Sun-like star from TESS and NGTS

“…To overcome this, we used spectral synthesis (with fixed values of eff , [Fe/H] and sin ) to model the wings of the magnesium triplets and sodium doublet. Uncertainties for log were calculated by perturbing log until the solution was no longer acceptable (Gill et al 2019). All our derived parameters for TIC-231005575 are set out in full in Table 3.…”

“…Such assessment requires diligent analysis of 1 , 2 , Age, and [Fe/H] with their respective uncertainties. We follow the method described by Gill et al (2019) to calculate the posterior probability distribution for the fractional radius residual, Δ 2 / , which we briefly describe here. We calculate the posterior probability distribution for the surface gravity of the M-dwarf, log 2 , and combine it with 2 to get a measured value for the radius of the M-dwarf, 2, .…”

NGTS and WASP photometric recovery of a single-transit candidate from TESS

“…We used wavelet analysis to extract atmospheric parameters from the co-added eight CORALIE spectroscopic observations of TIC-238855958 (Sect. 5) using the methodology set out in Gill et al (2018Gill et al ( , 2019. The co-added spectrum was re-sampled between 450-650 nm with 2 17 values.…”

TOI-222: a single-transit TESS candidate revealed to be a 34-d eclipsing binary with CORALIE, EulerCam, and NGTS

“…We re-sample between 450-650 nm with 2 17 values and co-add the spectra. We calculate the wavelet coefficients Wi=4-14 and fit the same coefficients with model spectra (identical to those used in Gill et al 2018 andGill et al 2019) in a Bayesian framework. We initiated 100 walkers and generated 10,000 draws as a burn-in phase.…”