Impact of occultations of stellar active regions on transmission spectra: Can occultation of a plage mimic the signature of a blue sky?

Abstract

Transmission spectroscopy during planetary transits, which is based on the measurements of the variations of planet-to-star radius ratio as a function of wavelength, is a powerful technique to study the atmospheric properties of transiting planets. One of the main limitation of this technique is the effects of stellar activity, which up until now, have been taken into account only by assessing the effect of non-occulted stellar spots on the estimates of planet-to-star radius ratio. In this paper, we study, for the first time, the impact of the occultation of a stellar spot and plage on the transmission spectra of transiting exoplanets. We simulated this effect by generating a large number of transit light curves for different transiting planets, stellar spectral types, and for different wavelengths. Results of our simulations indicate that the anomalies inside the transit light curve can lead to a significant underestimation or overestimation of the planet-to-star radius ratio as a function of wavelength. At short wavelengths, the effect can reach to a difference of up to 10% in the planet-to-star radius ratio, mimicking the signature of light scattering in the planetary atmosphere. Atmospheric scattering has been proposed to interpret the increasing slopes of transmission spectra toward blue for exoplanets HD 189733b and GJ 3470b. Here we show that these signatures can be alternatively interpreted by the occultation of stellar plages. Results also suggest that the best strategy to identify and quantify the effects of stellar activities on the transmission spectrum of a planet is to perform several observations during the transit epoch at the same wavelength. This will allow for identifying the possible variations in transit depth as a function of time due to stellar activity variability.

7 pages, 6 figures, Accepted for publication in A&A

References in corpus (7)

• Detection of atmospheric haze on an extrasolar planet: The 0.55 - 1.05 micron transmission spectrum of HD189733b with the Hubble Space Telescope
• Rayleigh scattering in the transit spectrum of HD 189733b
• Hubble Space Telescope times-series photometry of the planetary transit of HD189733: no moon, no rings, starspots
• Stellar activity of planetary host star HD 189733
• TiO and VO broad band absorption features in the optical spectrum of the atmosphere of the hot-Jupiter HD209458b
• A Spitzer Search for Water in the Transiting Exoplanet HD189733b
• Near-infrared transmission spectrum of the warm-uranus GJ 3470b with the Wide Field Camera-3 on the Hubble Space Telescope

Cited by in corpus (43)

• Detection of titanium oxide in the atmosphere of a hot Jupiter
• The Transit Light Source Effect II: The Impact of Stellar Heterogeneity on Transmission Spectra of Planets Orbiting Broadly Sun-like Stars
• Trends in Atmospheric Properties of Neptune-Size Exoplanets
• Transit Signatures of Inhomogeneous Clouds on Hot Jupiters: Insights From Microphysical Cloud Modeling
• Confirmation of WASP-107b's extended Helium atmosphere with Keck II/NIRSPEC
• Evidence for a spectroscopic direct detection of reflected light from 51 Peg b
• High-precision photometry by telescope defocussing. VII. The ultra-short period planet WASP-103
• Forecasting the Impact of Stellar Activity on Transiting Exoplanet Spectra
• Transmission spectroscopy of the inflated exoplanet WASP-52b, and evidence for a bright region on the stellar surface
• An HST/STIS Optical Transmission Spectrum of Warm Neptune GJ 436b
• Investigating the physical properties of transiting hot Jupiters with the 1.5-m Kuiper Telescope
• The Influence of Stellar Contamination on the Interpretation of Near Infrared Transmission Spectra of Sub-Neptune Worlds around M-Dwarfs
• Transiting the Sun: The impact of stellar activity on X-ray and ultraviolet transits
• Spectral variability of photospheric radiation due to faculae I: The Sun and Sun-like stars
• A Comprehensive Analysis of WASP-17b's Transmission Spectrum from Space-Based Observations
• Understanding stellar activity-induced radial velocity jitter using simultaneous K2 photometry and HARPS RV measurements
• The GTC exoplanet transit spectroscopy survey XI. Possible detection of Rayleigh scattering in the atmosphere of the Saturn-mass planet WASP-69b
• Activity and rotation of Kepler-17
• Broad-band spectrophotometry of HAT-P-32 b: Search for a scattering signature in the planetary spectrum
• High-precision multi-band time-series photometry of exoplanets Qatar-1b and TrES-5b
• 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
• Broadband transmission spectroscopy of HD209458b with ESPRESSO: Evidence for Na, TiO, or both
• LRG-BEASTS: Ground-based Detection of Sodium and a Steep Optical Slope in the Atmosphere of the Highly Inflated Hot-Saturn WASP-21b
• An enhanced slope in the transmission spectrum of the hot Jupiter WASP-104b
• ACCESS: Confirmation of a Clear Atmosphere for WASP-96b and a Comparison of Light Curve Detrending Techniques
• The GTC exoplanet transit spectroscopy survey VIII. Flat transmission spectrum for the warm gas giant WASP-80
• Sub-stellar Companions of Intermediate-mass Stars with CoRoT: CoRoT-34b, CoRoT-35b, and CoRoT-36b
• The GTC exoplanet transit spectroscopy survey X. Stellar spots versus Rayleigh scattering: the case of HAT-P-11b
• Obliquity measurement and atmospheric characterization of the WASP-74 planetary system
• Can stellar activity make a planet seem misaligned?
• Near-UV transit photometry of HAT-P-32 b with the LBT: Silicate aerosols in the planetary atmosphere
• Role of the impact parameter in exoplanet transmission spectroscopy
• Transmission spectroscopy of the hot Jupiter TrES-3 b: Disproof of an overly large Rayleigh-like feature
• Testing the solar activity paradigm in the context of exoplanet transits
• Atmospheric Characterization via Broadband Color Filters on the PLAnetary Transits and Oscillations of stars (PLATO) Mission
• CaRM: Exploring the chromatic Rossiter-McLaughlin effect. The cases of HD 189733b and WASP-127b
• On the Effect of Stellar Activity on Low-resolution Transit Spectroscopy and the Use of High Resolution as Mitigation
• Noise Sources in Photometry and Radial Velocities
• The ESPRESSO transmission spectrum of HD189733b : Extracting the planetary sodium and lithium signatures amid stellar contamination
• Transmission spectroscopy of WASP-7 b with UVES -- Detection of Na I D${}_2$ and tentative D${}_1$ line absorption
• Using Stellar Spectral Energy Distributions to Measure Exoplanet Parameters
• The impact of faculae on the radius determination of exoplanets: The case of the M-star GJ1214
• An Hα Transit of HD 189733b to Assess Stellar Activity Across the Transit Chord Close to JWST Observations