Astronomy & Telescopes

Detecting Exoplanet Transits With The Next Generation Of X-ray Telescopes

By Keith Cowing

Status Report

astro-ph.EP

August 15, 2024

Filed under astro-ph.EP, astronomy, atmosphere, AXIS, exoplanet, HD-189733 b, imaging, NewAthena, telescope, X-ray

Detecting Exoplanet Transits With The Next Generation Of X-ray Telescopes — Stellar and planetary properties of our sample. The left plot shows log X-ray flux at Earth (0.2-2.4 keV) vs log Rp R∗ 2 (%). Each planetary system in the sample is plotted, with the host star’s spectral type determining the color and shape. Points with dark outlines have measured X-ray fluxes, and points surrounded with purple circles are in the list of the top 15 candidate targets for AXIS and NewAthena. The method for determining each X-ray flux is given in section 2.1. For fluxes given in literature in a band other than 0.2-2.4 keV, we used the XSPEC models described in section 2.2 to convert the flux to 0.2-2.4 keV. The right plot shows the orbital period (days) and radii (Earth radii) of the planets in the NEA, with planets in our sample highlighted in blue squares. The top 15 candidate targets are shown with darker blue diamonds. The method for determining the top target candidates is described in Section 2.2. — astro-ph.IM

Detecting exoplanet transits at X-ray wavelengths would provide a window into the effects of high energy irradiation on the upper atmospheres of planets.

However, stars are relatively dim in the X-ray, making exoplanet transit detections difficult with current X-ray telescopes. To date, only one exoplanet (HD~189733~b) has an X-ray transit detection.

In this study, we investigate the capability of future X-ray observatories to detect more exoplanet transits, focusing on both the NewAthena-WFI instrument and the proposed Advanced X-ray Imaging Satellite (AXIS), which provide more light-collecting power than current instruments. We examined all the transiting exoplanet systems in the NASA Exoplanet Archive and gathered X-ray flux measurements or estimates for each host star.

We then predicted the stellar count rates for both AXIS and NewAthena and simulated light curves, using null-hypothesis testing to identify the top 15 transiting planets ranked by potential detection significance. We also evaluate transit detection probabilities when the apparent X-ray radius is enlarged due to atmospheric escape, finding that ≥5 of these planetary systems may be detectable on the >4σ level in this scenario.

Finally, we note that the assumed host star coronal temperature, which affects the shape of an X-ray transit, can also significantly affect our ability to detect the planet.

Raven Cilley, George W. King, Lia Corrales

Comments: Accepted for publication in AAS Journals
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); High Energy Astrophysical Phenomena (astro-ph.HE); Instrumentation and Methods for Astrophysics (astro-ph.IM)
Cite as: arXiv:2408.06417 [astro-ph.EP] (or arXiv:2408.06417v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2408.06417
Focus to learn more
Submission history
From: Lia Corrales
[v1] Mon, 12 Aug 2024 18:00:04 UTC (223 KB)
https://arxiv.org/abs/2408.06417
Astrobiology,

Keith Cowing

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻

Follow on Twitter