Modeling Stellar Surface Features on Subgiant Star with an M-dwarf Companion

Abstract

Understanding magnetic activity on the surface of stars other than the Sun is important for exoplanet analyses to properly characterize an exoplanet's atmosphere and to further characterize stellar activity on a wide range of stars. Modeling stellar surface features of a variety of spectral types and rotation rates are key to understanding of the magnetic activity of these stars. Using data from Kepler, we use the starspot modeling program STarSPot (STSP) to measure the position and size of spots for KOI-340 which is an eclipsing binary consisting of a subgiant star (${\mathrm{T}}_{\mathrm{eff}}=5593\pm 27K;{\mathrm{R}}_{\ast }=1.98\pm 0.05{\mathrm{R}}_{\odot }$) with an M-dwarf companion ($M_{\ast }=0.214\pm 0.006M_{\odot }$). STSP uses a novel technique to measure the spot positions and radii by using the transiting secondary to study and model individual active regions on the stellar surface using high-precision photometry. We find the average size of spot features on KOI-340's primary is $\sim$10% the radius of the star, i.e. two times larger than the mean size of Solar-maximum sunspots. The spots on KOI-340 are present at every longitude and show possible signs of differential rotation. The minimum fractional spotted area of KOI-340's primary is $2\begin{array}{c}+12\\ -2\end{array}\%$ while the spotted area of the Sun is at most 0.2%. One transit of KOI-340 shows a signal in the transit consistent with a plage; this plage occurs right before a dark spot indicating the plage and spot might be co-located on the surface of the star.

arXiv comment16 pages, 17 figures; Accepted to AJ

References in corpus (30)

• emcee: The MCMC Hammer
• Analytic Lightcurves for Planetary Transit Searches
• The generalised Lomb-Scargle periodogram. A new formalism for the floating-mean and Keplerian periodograms
• Accurate masses and radii of normal stars: modern results and applications
• batman: BAsic Transit Model cAlculatioN in Python
• Rotation Periods of 34,030 Kepler Main-Sequence Stars: The Full Autocorrelation Sample
• Measuring the rotation period distribution of field M-dwarfs with Kepler
• Planetary Candidates Observed by Kepler. VIII. A Fully Automated Catalog With Measured Completeness and Reliability Based on Data Release 25
• The Transit Light Source Effect: False Spectral Features and Incorrect Densities for M-dwarf Transiting Planets
• Water Vapor and Clouds on the Habitable-Zone Sub-Neptune Exoplanet K2-18b
• WASP-3b: a strongly-irradiated transiting gas-giant planet
• Hubble Space Telescope times-series photometry of the planetary transit of HD189733: no moon, no rings, starspots
• SOPHIE velocimetry of Kepler transit candidates VII. A false-positive rate of 35% for Kepler close-in giant exoplanet candidates
• Solar cycle prediction using precursors and flux transport models
• The theoretical calculation of the Rossby number and the `non-local' convective overturn time for pre-main sequence and early post-main sequence stars
• Disentangling the planet from the star in late type M dwarfs: A case study of TRAPPIST-1g
• Spectral Properties of Cool Stars: Extended Abundance Analysis of Kepler Objects of Interest
• Transit mapping of a starspot on CoRoT-2 - Probing a stellar surface by planetary transits
• Possible Bright Starspots on TRAPPIST-1
• CAFE: Calar Alto Fiber-fed Echelle spectrograph
• Stellar surface inhomogeneities as a potential source of the atmospheric signal detected in the K2-18 b transmission spectrum
• The 0.8-4.5$\mu$m broadband transmission spectra of TRAPPIST-1 planets
• Revisiting the connection between magnetic activity, rotation period, and convective turnover time for main-sequence stars
• Chromospheric Activity of HAT-P-11: an Unusually Active Planet-Hosting K Star
• Stellar Properties of Active G and K Stars: Exploring the Connection Between Starspots and Chromospheric Activity
• Near-infrared transmission spectrum of TRAPPIST-1 h using Hubble WFC3 G141 observations
• Stellar Magnetic Activity and "Butterfly Diagram" of Kepler-63
• Non-detection of Contamination by Stellar Activity in the Spitzer Transit Light Curves of TRAPPIST-1
• Are Starspots and Plages Co-Located on Active G and K Stars?
• Eclipsing binaries and fast rotators in the Kepler sample. Characterization via radial velocity analysis from Calar Alto