J/A+A/623/A57ivo://CDS.VizieR/J/A+A/623/A57doi:10.26093/cds/vizier.36230057CDSSalz M.Schneider P.C.Fossati L.Czesla S.France K.Schmitt J.H.M.M.2019-03-07T14:36:19Z2019-03-06T07:07:44ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.frmultiple-starsexoplanetsultraviolet-photometryClose-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 (200-270nm, 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 to 1.15 with three visits. We measure a broad-band 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-sigma 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 broad-band NUV 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.2019A&A...623A..57Shttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/623/A57CatalogResearchIsServedByTAP VizieR generic servicehttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/623/A57https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/623/A57http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/623/A57https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/623/A57https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/623/A57http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/623/A57GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapUVdefaultJ/A+A/623/A57/w121b-lcUV transit light curve of WASP-121bTimeBarycentric Julian date (TDB) (BJD-2450000)dtime.epochdoubleCRateCount ratect/sphot.count;em.UVdoublerecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordinte_CRateMean error on count ratect/sstat.errordouble