Description:
<jats:title>Abstract</jats:title>
<jats:p>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 is key to understanding the magnetic activity of these stars. Using data from Kepler, we use the starspot modeling program STarSPot (<jats:monospace>STSP</jats:monospace>) to measure the position and size of spots for KOI-340, which is an eclipsing binary consisting of a subgiant star (<jats:italic>T</jats:italic>
<jats:sub>eff</jats:sub> = 5593 ± 27 K, <jats:italic>R</jats:italic>
<jats:sub>⋆</jats:sub> = 1.98 ± 0.05 <jats:italic>R</jats:italic>
<jats:sub>⊙</jats:sub>) with an M-dwarf companion (<jats:italic>M</jats:italic>
<jats:sub>⋆</jats:sub> = 0.214 ± 0.006 <jats:italic>M</jats:italic>
<jats:sub>⊙</jats:sub>). <jats:monospace>STSP</jats:monospace> 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 that the average size of spot features on KOI-340's primary is ∼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 <jats:inline-formula>
<jats:tex-math>
<?CDATA ${2}_{-2}^{+12}{\rm{ \% }}$?>
</jats:tex-math>
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
<mml:msubsup>
<mml:mrow>
<mml:mn>2</mml:mn>
</mml:mrow>
<mml:mrow>
<mml:mo>−</mml:mo>
<mml:mn>2</mml:mn>
</mml:mrow>
<mml:mrow>
<mml:mo>+</mml:mo>
<mml:mn>12</mml:mn>
</mml:mrow>
</mml:msubsup>
<mml:mrow>
<mml:mi mathvariant="normal">%</mml:mi>
</mml:mrow>
</mml:math>
<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="ajac70caieqn1.gif" xlink:type="simple" />
</jats:inline-formula>, 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 that the plage and spot might be colocated on the surface of the star.</jats:p>