An extreme-mass ratio, short-period eclipsing binary consisting of a B dwarf primary and a pre-main-sequence M star companion discovered by KELT

Abstract

We present the discovery of KELT J072709+072007 (HD 58730), a very low mass ratio (q ≡ M2/M1 ≈ 0.07) eclipsing binary (EB) identified by the Kilodegree Extremely Little Telescope (KELT) survey. We present the discovery light curve and perform a global analysis of four high-precision ground-based light curves, the Transiting Exoplanets Survey Satellite (TESS) light curve, radial velocity (RV) measurements, Doppler Tomography (DT) measurements, and the broad-band spectral energy distribution (SED). Results from the global analysis are consistent with a fully convective (M2 = 0.22 ± 0.02M⊙) M star transiting a late-B primary ($M_1 = 3.34^{+0.07}_{-0.09} {M_\odot }; T_{\rm eff,1} = 11960^{+430}_{-520}\ {\rm K}$). We infer that the primary star is $183_{-30}^{+33}$ Myr old and that the companion star’s radius is inflated by 26 ± 8% relative to the predicted value from a low-mass isochrone of similar age. We separately and analytically fit for the variability in the out-of-eclipse TESS phase curve, finding good agreement between the resulting stellar parameters and those from the global fit. Such systems are valuable for testing theories of binary star formation and understanding how the environment of a star in a close-but-detached binary affects its physical properties. In particular, we examine how a star’s properties in such a binary might differ from the properties it would have in isolation.

Extreme mass ratios and fast rotation in three massive binaries

“…The masses and temperatures derived for the companions in our systems are compatible with low-mass stars, which would then still be in their PMS stage in view of the systems' ages and bloated radii of the companions. That interpretation was previously favored by several authors for objects presenting light curves and RV curves similar to those of our targets (Moe & Di Stefano 2015;Stevens et al 2020;Jerzykiewicz et al 2021;Stassun et al 2021;Johnston et al 2021).…”

“…No full light curve fitting nor velocity analysis was presented, however. Stevens et al (2020) analyzed the case of HD 58730, whose primary has a later spectral type, B9V, than our targets but shares with them a rather fast rotation ( sin( ) =183 km s −1 ). Reflection effects are not detected in the light curve of such a latetype B-star, but both ellipsoidal variations and narrow eclipses are present in its 3.6 d cycle.…”

HIP 33609 b: An Eccentric Brown Dwarf Transiting a V = 7.3 Rapidly Rotating B Star

“…The HIP 33609 system also extends our knowledge of transiting companions around hot stars. All previously discovered transiting companions around B-and A-type stars have orbital periods less than 10 days (Shporer et al 2014;Morton et al 2016;Gaudi et al 2017;Lund et al 2017;Talens et al 2017;Anderson et al 2018;Johnson et al 2018;Hellier et al 2019;Zhou et al 2019;Dorval et al 2020;Stevens et al 2020;Addison et al 2021;Giacalone et al 2022), whereas HIP 33609 provides the first companion on a long-period orbit (∼39 days).…”

Identifying Periodic Variable Stars and Eclipsing Binary Systems with Long-Term Las Cumbres Observatory Photometric Monitoring of ZTF J0139+5245

“…It has enabled follow-up observations for exoplanet transit surveys such as the Kilodegree Extremely Little Telescope survey (e.g. Ahlers et al 2020;Stevens et al 2020;Rodríguez Martínez et al 2020), which has discovered a number of planets around bright stars. LCO is leading the detection and tracking of near Earth objects (NEOs) and asteroids (e.g.…”