Magnetic Inflation and Stellar Mass. I. Revised Parameters for the Component Stars of the Kepler Low-mass Eclipsing Binary T-Cyg1-12664

Abstract

Several low-mass eclipsing binary stars show larger than expected radii for their measured mass, metallicity, and age. One proposed mechanism for this radius inflation involves inhibited internal convection and starspots caused by strong magnetic fields. One particular eclipsing binary, T-Cyg1-12664, has proven confounding to this scenario. Çakırlı et al. measured a radius for the secondary component that is twice as large as model predictions for stars with the same mass and age, but a primary mass that is consistent with predictions. Iglesias-Marzoa et al. independently measured the radii and masses of the component stars and found that the radius of the secondary is not in fact inflated with respect to models, but that the primary is, which is consistent with the inhibited convection scenario. However, in their mass determinations, Iglesias-Marzoa et al. lacked independent radial velocity measurements for the secondary component due to the star's faintness at optical wavelengths. The secondary component is especially interesting, as its purported mass is near the transition from partially convective to a fully convective interior. In this article, we independently determined the masses and radii of the component stars of T-Cyg1-12664 using archival Kepler data and radial velocity measurements of both component stars obtained with IGRINS on the Discovery Channel Telescope and NIRSPEC and HIRES on the Keck Telescopes. We show that neither of the component stars is inflated with respect to models. Our results are broadly consistent with modern stellar evolutionary models for main-sequence M dwarf stars and do not require inhibited convection by magnetic fields to account for the stellar radii.

Magnetic Inflation and Stellar Mass. IV. Four Low-mass Kepler Eclipsing Binaries Consistent with Non-magnetic Stellar Evolutionary Models

“…The secondary component is one of only a handful fully-convective lowmass stars with empirically measured masses and radii. Combined with KIC 10935310 from Han et al (2017), we find all our mass and radius measurements for low-mass Kepler eclipsing binary stars are consistent with modern stellar evolutionary models for M dwarf stars and do not require inhibited convection by magnetic fields to account for the stellar radii.…”

“…We adopted the mean of the radial velocities returned for each order as the measured radial velocity, and adopted the uncertainty by calculat-2 https://phoenix.ens-lyon.fr/Grids/BT-Settl ing the standard deviation of the radial velocities across the orders and dividing by the square root of number of orders used. The detailed procedure can be found in Han et al (2017). The top panel in Figure 3 shows a sample IGRINS H-band telluric-corrected spectrum of KIC 7605600 (in blue) and two BT-Settl spectra (in red and green).…”

Exploring the M-dwarf Luminosity–Temperature–Radius relationships using Gaia DR2

“…Again it has long been known that the eclipsing binaries show that M-star E-mail: smorrell@astro.ex.ac.uk radii appear to be inflated for their mass (see for example Figure 2 of Chen et al 2014;Chaturvedi et al 2018;Parsons et al 2018;Mann et al 2019), though Torres (2013) highlighted that the effect is subtle. Furthermore there can be significant discrepancies between parameter determinations for the same binary, see for example the discussion of T-Cyg1-12664 in Han et al (2017), or the difference in measured radius for the secondary in PTFEB132.707+19.810/AD 3814 (Kraus et al 2017;Gillen et al 2017). Nevertheless, at face value the failure of the models to match the eclipsing binaries in the mass-radius plane implies that the stellar structure models are incorrect.…”

The Rotation of M Dwarfs Observed by the Apache Point Galactic Evolution Experiment

“…It is hypothesized that fully convective M dwarfs, generally those with spectral types M4 and later, are unable to efficiently shed angular momentum through the interaction between the stellar wind and the stellar magnetic field, and therefore spin down more slowly over time (Stassun et al 2011). Also, some M dwarfs appear to have inflated radii, which may also be a consequence of magnetic activity (e.g., Feiden & Chaboyer 2014, Jackson & Jeffries 2014, Han et al 2017.…”