Monthly Notices of the Royal Astronomical Society | 2019
KOI-3890: a high-mass-ratio asteroseismic red giant+M-dwarf eclipsing binary undergoing heartbeat tidal interactions
Abstract
KOI-3890 is a highly eccentric, 153-day period eclipsing, single-lined spectroscopic binary system containing a red-giant star showing solar-like oscillations alongside tidal interactions. The combination of transit photometry, radial velocity observations, and asteroseismology have enabled the detailed characterisation of both the red-giant primary and the M-dwarf companion, along with the tidal interaction and the geometry of the system. The stellar parameters of the red-giant primary are determined through the use of asteroseismology and grid-based modelling to give a mass and radius of $M_{\\star}=1.04\\pm0.06\\;\\textrm{M}_{\\odot}$ and $R_{\\star}=5.8\\pm0.2\\;\\textrm{R}_{\\odot}$ respectively. When combined with transit photometry the M-dwarf companion is found to have a mass and radius of $M_{\\mathrm{c}}=0.23\\pm0.01\\;\\textrm{M}_{\\odot}$ and $R_{\\mathrm{c}}=0.256\\pm0.007\\;\\textrm{R}_{\\odot}$. Moreover, through asteroseismology we constrain the age of the system through the red-giant primary to be $9.1^{+2.4}_{-1.7}\\;\\mathrm{Gyr}$. This provides a constraint on the age of the M-dwarf secondary, which is difficult to do for other M-dwarf binary systems. In addition, the asteroseismic analysis yields an estimate of the inclination angle of the rotation axis of the red-giant star of $i=87.6^{+2.4}_{-1.2}$ degrees. The obliquity of the system\\textemdash the angle between the stellar rotation axis and the angle normal to the orbital plane\\textemdash is also derived to give $\\psi=4.2^{+2.1}_{-4.2}$ degrees showing that the system is consistent with alignment. We observe no radius inflation in the M-dwarf companion when compared to current low-mass stellar models.