2019/01/29 by M. Salz, P. C. Schneider, L. Fossati +3
Physics and Astronomy · #Absorption (acoustics) #Astronomy and Astrophysical Research #Astrophysics and Star Formation Studies #Exoplanet #Hot Jupiter #Observatory #Photoevaporation #Photometry (optics) #Planet #Stellar, planetary, and galactic studies #Transit (satellite) #Ultraviolet #astro-ph.EP
paper · pdf · doi:10.1051/0004-6361/201732419
published as A&A 623, A57 (2019) · 7 pages, 6 figures, accepted for publication in A&A
arxiv created 2019/01/29 · openalex publication_date 2019/01/29 · openalex created_date 2019/02/21 · arxiv updated 2019/03/06 · openalex updated_date 2026/08/05
Close-in gas planets are subject to continuous photoevaporation that can erode their volatile envelopes. Today, ongoing mass loss has been confirmed in a few individual systems via transit observations in the ultraviolet spectral range. We demonstrate that the Ultraviolet/Optical Telescope (UVOT) onboard the Neil Gehrels Swift Observatory enables photometry to a relative accuracy of about 0.5% and present the first near-UV (200–270 nm, NUV) transit observations of WASP-121 b, a hot Jupiter with one of the highest predicted mass-loss rates. The data cover the orbital phases 0.85–1.15 with three visits. We measure a broadband NUV transit depth of 2.10 ± 0.29%. While still consistent with the optical value of 1.55%, the NUV data indicate excess absorption of 0.55% at a 1.9 σ level. Such excess absorption is known from the WASP-12 system, and both of these hot Jupiters are expected to undergo mass loss at extremely high rates. With a Cloudy simulation, we show that absorption lines of Fe II in a dense extended atmosphere can cause broadband near-UV absorption at the 0.5% level. Given the numerous lines of low-ionization metals, the NUV range is a promising tracer of photoevaporation in the hottest gas planets.