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.

arXiv comment14 pages, 9 figures, accepted to AJ

References in corpus (29)

• emcee: The MCMC Hammer
• The Sloan Digital Sky Survey: Technical Summary
• The Transiting Exoplanet Survey Satellite
• The James Webb Space Telescope
• A new extensive library of PHOENIX stellar atmospheres and synthetic spectra
• Rotation Periods of 34,030 Kepler Main-Sequence Stars: The Full Autocorrelation Sample
• AstroImageJ: Image Processing and Photometric Extraction for Ultra-Precise Astronomical Light Curves
• AstroImageJ: Image Processing and Photometric Extraction for Ultra-Precise Astronomical Light Curves (Expanded Edition)
• HAT-P-11b: A Super-Neptune Planet Transiting a Bright K Star in the Kepler Field
• The Transit Light Source Effect: False Spectral Features and Incorrect Densities for M-dwarf Transiting Planets
• The CHEOPS mission
• Starspots, spin-orbit misalignment, and active latitudes in the HAT-P-11 exoplanetary system
• 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
• HAT-P-11: Discovery of a Second Planet and a Clue to Understanding Exoplanet Obliquities
• Starspot distributions on fully convective M dwarfs: implications for radial velocity planet searches
• Transit mapping of a starspot on CoRoT-2 - Probing a stellar surface by planetary transits
• 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
• The HST PanCET Program: Hints of Na I & Evidence of a Cloudy Atmosphere for the Inflated Hot Jupiter WASP-52b
• Starspot occultations in infrared transit spectroscopy: the case of WASP-52b
• 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
• Stellar Magnetic Activity and "Butterfly Diagram" of Kepler-63
• High Fidelity Imaging of the Inner AU Mic Debris Disk: Evidence of Differential Wind Sculpting?
• 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

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