Transiting the Sun: The impact of stellar activity on X-ray and ultraviolet transits

Abstract

Transits of hot Jupiters in X-rays and the ultraviolet have been shown to be both deeper and more variable than the corresponding optical transits. This variability has been attributed to hot Jupiters having extended atmospheres at these wavelengths. Using resolved images of the Sun from NASA's Solar Dynamics Observatory spanning 3.5 years of Solar Cycle 24 we simulate transit light curves of a hot Jupiter to investigate the impact of Solar like activity on our ability to reliably recover properties of the planet's atmosphere in soft X-rays (94 Å), the UV (131-1700 Å), and the optical (4500 Å). We find that for stars with similar activity levels to the Sun, the impact of stellar activity results in the derived radius of the planet in soft X-ray/EUV to be underestimated by up-to 25% or overestimated by up-to 50% depending on whether the planet occults active regions. We also find that in up-to 70% of the X-ray light curves the planet transits over bright star spots. In the far ultraviolet (1600 & 1700 Å), we find the mean recovered value of the planet-to-star radius ratio to be over-estimated by up-to 20%. For optical transits we are able to consistently recover the correct planetary radius. We also address the implications of our results for transits of WASP-12b and HD 189733b at short wavelengths.

Accepted for publication in ApJ

References in corpus (10)

• Lyman-$\alpha$ Transit Spectroscopy and the Neutral Hydrogen Tail of the Hot Neptune GJ436b
• Near-UV Absorption, Chromospheric Activity, and Star-Planet Interactions in the WASP-12 system
• HST/STIS Optical Transit Transmission Spectra of the hot-Jupiter HD209458b
• Early UV Ingress in WASP-12b: Measuring Planetary Magnetic Fields
• Impact of occultations of stellar active regions on transmission spectra: Can occultation of a plage mimic the signature of a blue sky?
• Rayleigh scattering by H2 in the extrasolar planet HD209458b
• Hubble Space Telescope detection of oxygen in the atmosphere of exoplanet HD189733b
• The shocking transit of WASP-12b: Modelling the observed early ingress in the near ultraviolet
• A cool starspot or a second transiting planet in the TrES-1 system?
• Stellar Differential Rotation and Coronal Timescales

Cited by in corpus (5)

• The Transit Light Source Effect II: The Impact of Stellar Heterogeneity on Transmission Spectra of Planets Orbiting Broadly Sun-like Stars
• Investigating the physical properties of transiting hot Jupiters with the 1.5-m Kuiper Telescope
• Near-ultraviolet Transmission Spectroscopy of HD 209458b: Evidence of Ionized Iron Beyond the Planetary Roche Lobe
• Ultraviolet C II and Si III Transit Spectroscopy and Modeling of the Evaporating Atmosphere of GJ436b
• MOVES III. Simultaneous X-ray and ultraviolet observations unveiling the variable environment of the hot Jupiter HD 189733b