spotrod: a semi-analytic model for transits of spotted stars

Abstract

The Hubble Space Telescope (HST) and the Kepler space mission observed a large number of planetary transits showing anomalies due to starspot eclipses, with more such observations expected in the near future by the K2 mission and the Transiting Exoplanet Survey Satellite (TESS). To facilitate analysis of this phenomenon, we present spotrod, a model for planetary transits of stars with an arbitrary limb darkening law and a number of homogeneous, circular spots on their surface. A free, open source implementation written in C, ready to use in Python, is available for download. We analyze Kepler observations of the planetary host star HAT-P-11, and study the size and contrast of more than two hundred starspots. We find that the flux ratio of spots ranges at least from 0.6 to 0.9, corresponding to an effective temperature approximately 100 to 450 K lower than the stellar surface, although it is possible that some spots are darker than 0.5. The largest detected spots have a radius less than approximately 0.2 stellar radii.

16 pages, 15 figures. Accepted for publication in MNRAS volume 442 issue 4

References in corpus (3)

• Hubble Space Telescope times-series photometry of the planetary transit of HD189733: no moon, no rings, starspots
• A cool starspot or a second transiting planet in the TrES-1 system?
• Stellar rotation--planetary orbit period commensurability in the HAT-P-11 system

Cited by in corpus (11)

• The Transit Light Source Effect II: The Impact of Stellar Heterogeneity on Transmission Spectra of Planets Orbiting Broadly Sun-like Stars
• The Starspots of HAT-P-11: Evidence for a Solar-like Dynamo
• An Exomoon Survey of 70 Cool Giant Exoplanets and the New Candidate Kepler-1708 b-i
• Transmission spectroscopy of the inflated exoplanet WASP-52b, and evidence for a bright region on the stellar surface
• The stellar obliquity, planet mass, and very low albedo of Qatar-2 from K2 Photometry
• ACCESS: A Visual to Near-infrared Spectrum of the Hot Jupiter WASP-43b with Evidence of ${\mathrm{H}}_2\mathrm{O}$, but no evidence of Na or K
• ACCESS: Ground-based Optical Transmission Spectroscopy of the Hot Jupiter WASP-4b
• Disentangling planetary and stellar activity features in the CoRoT-2 light curve
• TOSC: an algorithm for the tomography of spotted transit chords
• Noise Sources in Photometry and Radial Velocities
• Stellar activity and transits