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

Joe Llama, E. L. Shkolnik

Research output: Contribution to journalArticlepeer-review

25 Citations (Scopus)

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 yr 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 activity levels similar to those of the Sun, the impact of stellar activity results in underestimating the derived radius of the planet in soft X-ray/EUV by up-to 25% or overestimating it by up to 50% depending on whether the planet occultsactive regions. We also find that in up to 70% of the X-ray light curves the planet transits over bright starspots. In the far-ultraviolet (1600 Å and 1700 Å), we find the mean recovered value of Rp/R* 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-12 b and HD 189733b at short wavelengths.
Original languageEnglish
Number of pages10
JournalAstrophysical Journal
Volume802
Issue number1
DOIs
Publication statusPublished - 19 Mar 2015

Keywords

  • Planets and satellites: atmospheres
  • Planets and satellites: individual: HD 189733b
  • WASP-12b
  • Stars: activity
  • Stars: coronae
  • Starspots

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