Planetary Parameters, XUV Environments, and Mass-loss Rates for Nearby Gaseous Planets with X-Ray-detected Host Stars

Abstract

We leverage Gaia DR2 parallactic distances to deliver new or revised estimates of planetary parameters and X-ray irradiation for a distance-limited (≲100 pc) sample of 27 gaseous planets (from super-Earths to hot Jupiters) with publicly available Chandra and/or XMM observations, for which we carry out a homogeneous data reduction. For 20 planets with X-ray-detected host stars we make use of the photoionization hydrodynamics code ATES to derive updated atmospheric mass outflow rates. The newly derived masses/radii are not consistent with the exoplanet.eu values for five systems: HD 149026b and WASP-38, for mass, and Au Mic b, HAT-P-20, and HAT-P-2 for radii. Notably, the lower mass implies a (Saturn-like) density of 0.86 ± 0.09 g cm−3 for HD 149026b. This independent estimate is consistent with the lowest values reported in the literature. Separately, we report on the X-ray detection of GJ 9827, HD 219134, and LHS 1140 for the first time. The inferred stellar X-ray luminosity of LHS 1140 ( 1.34 − 0.21 + 0.19 × 10 26 erg s−1) implies that LHS 1140 b is the least irradiated transiting super-Earth known to orbit within the habitable zone of a nearby M dwarf.

Exoplanet Aeronomy: A Case Study of WASP-69 b’s Variable Thermosphere

“…This yielded a 95% confidence interval on the number of source counts to be [0-11.5], with the upper end of this interval corresponding to a count rate of 0.9 ks −1 . To convert this result to a X-ray flux from WASP-69, we scaled the two-temperature APEC model fit to the 2016 XMM-Newton observation by Spinelli et al (2023b) so that the model Swift count rate indicated by Xspec matched our statistical upper limit for the measured count rate. While X-ray spectral shapes can change with varying flux, especially during flares, we did not detect any flares (see Section 4.2).…”

“…We found the 95% upper limit on the 0.3-2.4 keV unabsorbed flux to be 2.6 × 10 −14 erg cm −2 s −1 . For comparison, the bestfit model published by Spinelli et al (2023b) from XMM-Newton observations in 2016 predicts a flux of -+ 5.19 0.17 0.23 -10 14 erg cm −2 s −1 in the same 0.3-2.4 keV energy range. The archival XMM-Newton flux is 2 times larger than the Swift XRT upper limit from 2023, and we show these data on the timeline in Figure 6.…”

“…Here, we present new metastable HeI results from a transit of WASP-69 b viewed by the Wide Field InfraRed Camera (WIRC; Wilson et al 2003) at Palomar Observatory and highenergy observations from the Neil Gehrels Swift Observatory (Swift) that were taken within a 1 month window. Combining these measurements with archival metastable HeI (Nortmann et al 2018;Vissapragada et al 2020Vissapragada et al , 2022bAllart et al 2023;Guilluy et al 2024;Tyler et al 2024) and high-energy (Nortmann et al 2018;Spinelli et al 2023b) observations provides a powerful assessment of WASP-69 b's outflow variability. The bright (J = 8.0 mag) host star and large scale height of the hot Jupiter companion (0.26 M J , 1.06 R J ; Anderson et al 2014) make the WASP-69 system an exceptional target for studies seeking to quantify the time variability of atmospheric outflows.…”