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Register a new userAn Extreme-mass Ratio, Short-period Eclipsing Binary Consisting of a B Dwarf Primary and a Pre-main Sequence M Star Companion Discovered by KELT
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We present the discovery of thisstar (HD 58730), a very low mass ratio ($q equiv M_2/M_1 approx 0.07$) 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 ($M_2 = 0.22 pm 0.02 M_{odot})$ 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 stars radius is inflated by $26 pm 8%$ 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 stars properties in such a binary might differ from the properties it would have in isolation.
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We present Mon-735, a detached double-lined eclipsing binary (EB) member of the $sim$3 Myr old NGC 2264 star forming region, detected by Spitzer. We simultaneously model the Spitzer light curves, follow-up Keck/HIRES radial velocities, and the systems spectral energy distribution to determine self-consistent masses, radii and effective temperatures for both stars. We find that Mon-735 comprises two pre-main sequence M dwarfs with component masses of $M = 0.2918 pm 0.0099$ and $0.2661 pm 0.0095$ $rm{M}_{odot}$, radii of $R = 0.762 pm 0.022$ and $0.748 pm 0.023$ $rm{R}_{odot}$, and effective temperatures of $T_{rm eff} = 3260 pm 73$ and $3213 pm 73$ $rm{K}$. The two stars travel on circular orbits around their common centre of mass in $P = 1.9751388 pm 0.0000050$ days. We compare our results for Mon-735, along with another EB in NGC 2264 (CoRoT 223992193), to the predictions of five stellar evolution models. These suggest that the lower mass EB system Mon-735 is older than CoRoT 223992193 in the mass-radius diagram (MRD) and, to a lesser extent, in the Hertzsprung-Russell diagram (HRD). The MRD ages of Mon-735 and CoRoT 223992193 are $sim$7-9 and 4-6 Myr, respectively, with the two components in each EB system possessing consistent ages.
Hot subdwarf B stars (sdBs) are evolved, core helium-burning objects located on the extreme horizontal branch. Their formation history is still puzzling as the sdB progenitors must lose nearly all of their hydrogen envelope during the red-giant phase. About half of the known sdBs are in close binaries with periods from 1.2 h to a few days, a fact that implies they experienced a common-envelope phase. Eclipsing hot subdwarf binaries (also called HW Virginis systems) are rare but important objects for determining fundamental stellar parameters. Even more significant and uncommon are those binaries containing a pulsating sdB, as the mass can be determined independently by asteroseismology. Here we present a first analysis of the eclipsing hot subdwarf binary V2008-1753. The light curve shows a total eclipse, a prominent reflection effect, and low--amplitude pulsations with periods from 150 to 180 s. An analysis of the light-- and radial velocity (RV) curves indicates a mass ratio close to $ q = 0.146$, an RV semi-amplitude of $K=54.6 ,rm kms^{-1}$, and an inclination of $i=86.8^circ$. Combining these results with our spectroscopic determination of the surface gravity, $log ,g = 5.83$, the best--fitting model yields an sdB mass of 0.47$M_{rm odot}$ and a companion mass of $69 M_{rm Jup}$. As the latter mass is below the hydrogen-burning limit, V2008-1753 represents the first HW Vir system known consisting of a pulsating sdB and a brown dwarf companion. Consequently, it holds great potential for better constraining models of sdB binary evolution and asteroseismology.
We report the discovery of KELT J041621-620046, a moderately bright (J$sim$10.2) M dwarf eclipsing binary system at a distance of 39$pm$3 pc. KELT J041621-620046 was first identified as an eclipsing binary using observations from the Kilodegree Extremely Little Telescope (KELT) survey. The system has a short orbital period of $sim$1.11 days and consists of components with M$_1$ = $0.447^{-0.047}_{+0.052},M_odot$ and M$_2$ = $0.399^{-0.042}_{+0.046},M_odot$ in nearly circular orbits. The radii of the two stars are R$_1$ = $0.540^{-0.032}_{+0.034},R_odot$ and R$_2$ = $0.453pm0.017,R_odot$. Full system and orbital properties were determined (to $sim$10% error) by conducting an EBOP global modeling of the high precision photometric and spectroscopic observations obtained by the KELT Follow-up Network. Each star is larger by 17-28% and cooler by 4-10% than predicted by standard (non-magnetic) stellar models. Strong H$alpha$ emission indicates chromospheric activity in both stars. The observed radii and temperature discrepancies for both components are more consistent with those predicted by empirical relations that account for convective suppression due to magnetic activity.
EPIC 216747137 is a new HW~Virginis system discovered by the Kepler spacecraft during its K2 second life. Like the other HW Vir systems, EPIC 216747137 is a post-common-envelope eclipsing binary consisting of a hot subluminous star and a cool low-mass companion. The short orbital period of 3.87 hours produces a strong reflection effect from the secondary (~9% in the R band). Together with AA Dor and V1828 Aql, EPIC 216747137 belongs to a small subgroup of HW Vir systems with a hot evolved sdOB primary. We find the following atmospheric parameters for the hot component: Teff=40400$pm$1000 K, logg=5.56$pm$0.06, log(N(He)/N(H))=$-$2.59$pm$0.05. The sdOB rotational velocity vsini=51$pm$10 km/s implies that the stellar rotation is slower than the orbital revolution and the system is not synchronized. When we combine photometric and spectroscopic results with the Gaia parallax, the best solution for the system corresponds to a primary with a mass of about 0.62 Msun close to, and likely beyond, the central helium exhaustion, while the cool M-dwarf companion has a mass of about 0.11 Msun.
In this paper, we derive the fundamental properties of 1SWASPJ011351.29+314909.7 (J0113+31), a metal-poor (-0.40 +/- 0.04 dex), eclipsing binary in an eccentric orbit (~0.3) with an orbital period of ~14.277 d. Eclipsing M dwarfs orbiting solar-type stars (EBLMs), like J0113+31, have been identified from WASP light curves and follow-up spectroscopy in the course of the transiting planet search. We present the first binary of the EBLM sample to be fully analysed, and thus, define here the methodology. The primary component with a mass of 0.945 +/- 0.045 Msun has a large radius (1.378 +/- 0.058 Rsun) indicating that the system is quite old, ~9.5 Gyr. The M-dwarf secondary mass of 0.186 +/- 0.010 Msun and radius of 0.209 +/- 0.011 Rsun are fully consistent with stellar evolutionary models. However, from the near-infrared secondary eclipse light curve, the M dwarf is found to have an effective temperature of 3922 +/- 42 K, which is ~600 K hotter than predicted by theoretical models. We discuss different scenarios to explain this temperature discrepancy. The case of J0113+31 for which we can measure mass, radius, temperature and metallicity, highlights the importance of deriving mass, radius and temperature as a function of metallicity for M dwarfs to better understand the lowest mass stars. The EBLM Project will define the relationship between mass, radius, temperature and metallicity for M dwarfs providing important empirical constraints at the bottom of the main sequence.
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