Measuring the Temperature of Starspots from Multi-Filter Photometry

Abstract

Using simultaneous multi-filter observations during the transit of an exoplanet around a K dwarf star, we determine the temperature of a starspot through modeling the radius and position with wavelength-dependent spot contrasts. We model the spot using the starspot modeling program STarSPot (STSP), which uses the transiting companion as a knife-edge probe of the stellar surface. The contrast of the spot, i.e. the ratio of the integrated flux of a darker spot region to the star's photosphere, is calculated for a range of filters and spot temperatures. We demonstrate this technique using simulated data of HAT-P-11, a K dwarf (T = 4780 K) with well-modeled starspot properties for which we obtained simultaneous multi-filter transits using LCO's MuSCAT3 instrument on the 2-meter telescope at Haleakala Observatory which allows for simultaneous, multi-filter, diffuser assisted high-precision photometry. We determine the average (i.e. a combination of penumbra and umbra) spot temperature for HAT-P-11's spot complexes is 4500 K $\pm$ 100 K using this technique. We also find for our set of filters that comparing the SDSS g' and i' filters maximizes the signal difference caused by a large spot in the transit. Thus, this technique allows for the determination of the average spot temperature using only one spot occultation in transit and can provide simultaneous information on the spot temperature and spot properties.

14 pages, 9 figures, accepted to AJ

References in corpus (11)

• The Transiting Exoplanet Survey Satellite
• The James Webb Space Telescope
• Hubble Space Telescope times-series photometry of the planetary transit of HD189733: no moon, no rings, starspots
• The Starspots of HAT-P-11: Evidence for a Solar-like Dynamo
• Towards Space-like Photometric Precision from the Ground with Beam-Shaping Diffusers
• From Starspots to Stellar Coronal Mass Ejections -- Revisiting Empirical Stellar Relations
• WASP-52b. The effect of starspot correction on atmospheric retrievals
• Persistent starspot signals on M dwarfs: multi-wavelength Doppler observations with the Habitable-zone Planet Finder and Keck/HIRES
• Chromospheric Activity of HAT-P-11: an Unusually Active Planet-Hosting K Star
• Rotation periods of TESS Objects of Interest from the Magellan-TESS Survey with multiband photometry from Evryscope and TESS
• Observationally Constraining the Starspot Properties of Magnetically Active M67 Sub-Subgiant S1063

Cited by in corpus (4)

• JWST/NIRISS reveals the water-rich "steam world" atmosphere of GJ 9827 d
• Multi-band, Multi-epoch Photometry of the Spot-crossing System TOI-3884: Refined System Geometry and Spot Properties
• Quantifying the Impact of Starspot-Crossing Events on Retrieved Parameters from Transit Lightcurves
• Twinkle Twinkle Little Star, Roman Sees Where You Are: Predicting Exoplanet Transit Yields in the Rosette Nebula with the Nancy Grace Roman Space Telescope