Transiting the Sun II: The impact of stellar activity on Lyman-$\alpha$ transits

Abstract

High-energy observations of the Sun provide an opportunity to test the limits of our ability to accurately measure properties of transiting exoplanets in the presence of stellar activity. Here we insert transits of a hot Jupiter into continuous disk integrated data of the Sun in Lyman-alpha (Ly$\alpha$) from NASA's SDO/EVE instrument to assess the impact of stellar activity on the measured planet-to-star radius ratio $({\text{R}}_{\text{p}}/{\text{R}}_{\star })$. In 75% of our simulated light curves we measure the correct radius ratio; however, incorrect values can be measured if there is significant short term variability in the light curve. The maximum measured value of $({\text{R}}_{\text{p}}/{\text{R}}_{\star })$ is $50\%$ larger than the input value, which is much smaller than the large Ly$\alpha$ transit depths that have been reported in the literature, suggesting that for stars with activity levels comparable to the Sun, stellar activity alone cannot account for these deep transits. We ran simulations without a transit and found that stellar activity cannot mimic the Ly$\alpha$ transit of 55 Cancari b, strengthening the conclusion that this planet has a partially transiting exopshere. We were able to compare our simulations to more active stars by artificially increasing the variability in the Solar Ly$\alpha$ light curve. In the higher variability data, the largest value of $({\text{R}}_{\text{p}}/{\text{R}}_{\star })$ we measured is < 3x the input value which again is not large enough to reproduce the Ly$\alpha$ transit depth reported for the more active stars HD 189733 and GJ 436, supporting the interpretation that these planets have extended atmospheres and possible cometary tails.

Accepted for publication in ApJ

References in corpus (13)

• Atmospheric Escape from Hot Jupiters
• KEPLER's First Rocky Planet: Kepler-10b
• A giant comet-like cloud of hydrogen escaping the warm Neptune-mass exoplanet GJ 436b
• 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
• Early UV Ingress in WASP-12b: Measuring Planetary Magnetic Fields
• HAZMAT I: The Evolution of Far-UV and Near-UV Emission from Early M Stars
• Atmospheric escape from HD 189733b observed in HI Lyman-alpha: detailed analysis of HST/STIS September 2011 observations
• 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
• The effect of Lyman $\alpha$ radiation on mini-Neptune atmospheres around M stars: application to GJ 436b
• Transiting the Sun: The impact of stellar activity on X-ray and ultraviolet transits
• The Ly-alpha profile and center-to-limb variation of the quiet Sun

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• Reconnaissance of the TRAPPIST-1 exoplanet system in the Lyman-$\alpha$ line
• Detection of Ongoing Mass Loss from HD 63433c, a Young Mini Neptune
• On the Verge of an Astronomy CubeSat Revolution
• Near-ultraviolet Transmission Spectroscopy of HD 209458b: Evidence of Ionized Iron Beyond the Planetary Roche Lobe
• Effect of stellar flares on the upper atmospheres of HD 189733b and HD 209458b
• The GAPS Programme at TNG. XXXII. The revealing non-detection of metastable HeI in the atmosphere of the hot Jupiter WASP-80b
• Strong HI Lyman-$\alpha$ variations from the 11 Gyr-old host star Kepler-444: a planetary origin ?
• Modeling the Ly$\alpha$ transit absorption of the hot Jupiter HD 189733b
• TOI-1670 b and c: An Inner Sub-Neptune with an Outer Warm Jupiter Unlikely to have Originated from High-Eccentricity Migration
• Planetary transits at radio wavelengths: secondary eclipses of hot Jupiter extended atmospheres
• HORuS transmission spectroscopy and revised planetary parameters of KELT-7b
• Five new hot-Jupiter transits investigated with Swift-UVOT