DETECTING THE COMPANIONS AND ELLIPSOIDAL VARIATIONS OF RS CVN PRIMARIES. II.oDRACONIS, A CANDIDATE FOR RECENT LOW-MASS COMPANION INGESTION

Abstract

To measure the stellar and orbital properties of the metal-poor RS CVn binary o Draconis (o Dra), we directly detect the companion using interferometric observations obtained with the Michigan InfraRed Combiner at Georgia State University's Center for High Angular Resolution Astronomy (CHARA) Array. The H-band flux ratio between the primary and secondary stars is the highest confirmed flux ratio (370 ± 40) observed with long-baseline optical interferometry. These detections are combined with radial velocity data of both the primary and secondary stars, including new data obtained with the Tillinghast Reflector Echelle Spectrograph on the Tillinghast Reflector at the Fred Lawrence Whipple Observatory and the 2-m Tennessee State University Automated Spectroscopic Telescope at Fairborn Observatory. We determine an orbit from which we find model-independent masses and ages of the components (M A = 1.35 ± 0.05 M ⊙ , M B = 0.99 ± 0.02 M ⊙ , system age = 3.0 ∓ 0.5 Gyr). An average of a 23-year light curve of o Dra from the Tennessee State University Automated Photometric Telescope folded over the orbital period newly reveals eclipses and the quasi-sinusoidal signature of ellipsoidal variations. The modeled light curve for our system's stellar and orbital parameters confirm these ellipsoidal variations due to the primary star partially filling its Roche lobe potential, suggesting most of the photometric variations are not due to stellar activity (starspots). Measuring gravity darkening from the average light curve gives a best-fit of β = 0.07 ± 0.03, a value consistent with conventional theory for convective envelope stars. The primary star also exhibits an anomalously short rotation period, which, when taken with other system parameters, suggests the star likely engulfed a low-mass companion that had recently spun-up the star.

Multiplicity of Galactic Cepheids from long-baseline interferometry – III. Sub-percent limits on the relative brightness of a close companion of δ Cephei

“…The regular dynamic range reachable by the current beam combiners is about 5.8 mag (200:1), making this new possible companion of δ Cep hardly detectable from long-baseline interferometry, but not impossible as already demonstrated by Gallenne et al (2015) and Roettenbacher et al (2015), who detected components with a flux ratio of about 6.5 mag.…”

“…A companion might be detected at ρ ∼ 5 mas and P A ∼ −0.8 • , with a flux ratio of f ∼ 0.21 %, but other positions seem also possible with similar detection levels. Furthermore, such a flux ratio is below the average sensitivity limit reachable by the current beam combiners, but two components were already detected with such a contrast (Roettenbacher et al 2015;Gallenne et al 2015). The second dataset (October) gives a best fit at a detection level of 3.1σ both for all observables and only the CPs, but at distinct locations and very different flux ratios.…”

Surface magnetism of cool stars

“…MIRC is the only instrument at the CHARA Array that can combine light from all the six telescopes, allowing for robust interferometric imaging (H-band). MIRC has been very successful in studying distorted fast rotators (e.g., Monnier et al 2007), interacting binaries (Zhao et al 2008), the mysterious eclipse of Aurigae (Kloppenborg et al 2010), and components of binary stars up to the flux ratio of 370±40 (Roettenbacher et al 2015).…”

EXPRES. III. Revealing the Stellar Activity Radial Velocity Signature of $ε$ Eridani with Photometry and Interferometry

“…Plages and networks are also bright with respect to the photosphere, but have a more significant RV amplitude contribution on the order of a few m s −1 , as seen on the Sun (Milbourne et al 2019). Starspots are dark features against the photosphere and can cause line profile distortions that contribute a wide range of RV amplitudes-from less than 1 m s −1 to several km s −1 for large starspots (Roettenbacher et al 2015;Haywood et al 2016). Even for chromospherically quiet stars, these signatures can overwhelm the ∼ 10 cm s −1 RV signature of an Earth analog in the habitable zone.…”