Stellar Properties of KIC 8736245: An Eclipsing Binary with a Solar-type Star Leaving the Main Sequence

Abstract

There is a well-known stellar parameter discrepancy for late K and M dwarfs, in that the observed radii and temperatures are often respectively larger and cooler than predicted by theory by several percent. In an on-going effort to elucidate this issue, we examine the double-lined Kepler eclipsing binary star system KIC 8736245. We supplement the near-continuous 4-year Kepler light curve with ground-based multicolor photometry from Mount Laguna Observatory and spectroscopy from the Hobby-Eberly Telescope. The binary has an edge-on, circular 5.07 day orbit with stellar masses equal to $0.987\pm 0.009$ and $0.782\pm 0.009{\text{M}}_{\odot }$ and radii of $1.311\pm 0.006$ and $0.804\pm 0.004{\text{R}}_{\odot }$, respectively, and an estimated age of 7-9 Gyr. We find that the stellar radii are consistent with theoretical models within the uncertainties, whereas the temperature of the secondary star is $\sim$6% cooler than predicted. An important aspect of this work is that the uncertainties derived from a single epoch (individual night of observations) underestimates the overall system parameter uncertainties due to the effect of the 1-4% fluctuations caused by stellar activity. Our error estimates come from the spread in parameters measured at 8 epochs. From the periodicities in the light curve and from the eclipse times, we measure candidate spin periods to be approximately 4.98 and 5.87 days for the primary and secondary star. Surprisingly, these imply super- and sub-synchronous rotation compared to the orbital period. Thus KIC 8736245 serves as an interesting case study for the exchange of angular momentum and general stellar astrophysics as stars in binaries evolve off the main sequence.

arXiv comment15 pages, 12 figures, accepted to The Astronomical Journal

References in corpus (34)

• Astropy: A Community Python Package for Astronomy
• Binary companions of evolved stars in APOGEE DR14: Search method and catalog of ~5,000 companions
• The Dartmouth Stellar Evolution Database
• Accurate masses and radii of normal stars: modern results and applications
• Kepler Mission Design, Realized Photometric Performance, and Early Science
• Kepler Input Catalog: Photometric Calibration and Stellar Classification
• Overview of the Kepler Science Processing Pipeline
• Kepler Eclipsing Binary Stars. I. Catalog and Principal Characterization of 1879 Eclipsing Binaries in the First Data Release
• Absolute dimensions of the M-type eclipsing binary YY Geminorum (Castor C): a challenge to evolutionary models in the lower main-sequence
• Kepler Eclipsing Binary Stars. VII. The Catalog of Eclipsing Binaries Found in the Entire Kepler Data-Set
• Kepler Eclipsing Binary Stars. II. 2165 Eclipsing Binaries in the Second Data Release
• Evolution of low-mass star and brown dwarf eclipsing binaries
• Initial Characteristics of Kepler Long Cadence Data For Detecting Transiting Planets
• On the Correlation between the Magnetic Activity Levels, the Metallicities and the Radii of Low-Mass Stars
• Introduction to astroML: Machine Learning for Astrophysics
• The radius discrepancy in low mass stars: single vs. binaries
• The Mass-Radius(-Rotation?) Relation for Low-Mass Stars
• Photometric detection of non-transiting short-period low-mass companions through the beaming, ellipsoidal and reflection effects in Kepler and CoRoT lightcurves
• Radial Velocity Studies of Close Binary Stars.VII. Methods and Uncertainties
• The effect of magnetic activity on low-mass stars in eclipsing binaries
• Masses and Radii of Low-Mass Stars: Theory versus Observations
• Kepler-1647b: the largest and longest-period Kepler transiting circumbinary planet
• Tidal Synchronization and Differential Rotation of Kepler Eclipsing Binaries
• Reevaluating the Mass-Radius Relation for Low-Mass, Main Sequence Stars
• The Eclipsing Binary V1061 Cygni: Confronting Stellar Evolution Models for Active and Inactive Solar-Type Stars
• Identification, Classifications, and Absolute Properties of 773 Eclipsing Binaries Found in the TrES Survey
• Fundamental properties of lower main-sequence stars
• Absolute dimensions of solar-type eclipsing binaries. II. V636 Centauri: A 1.05 Msun primary with an active, cool, oversize 0.85 Msun secondary
• 2MASS J05162881+2607387: A New Low-Mass Double-Lined Eclipsing Binary
• System Parameters of the Transiting Extrasolar Planet HD 209458b
• Time variation of Kepler transits induced by stellar rotating spots - a way to distinguish between prograde and retrograde motion I. Theory
• Kepler Studies of Low-Mass Eclipsing Binaries I. Parameters of the Long-Period Binary KIC 6131659
• T-Lyr1-17236: A Long-Period Low-Mass Eclipsing Binary
• Orbital and physical parameters of eclipsing binaries from the All-Sky Automated Survey catalogue - X. Three high-contrast systems with secondaries detected with IR spectroscopy

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