MASCARA-4 b light and RV curves

Simultaneous photometry was carried out with EulerCam installed at the Euler telescope to deliver updated system and planet parameters. We searched for atomic, ionic, and molecular species via individual absorption lines and cross-correlation techniques. These results are compared to literature studies on UHJs characterised to date.

With CORALIE and EulerCam observations, we updated the mass of MASCARA-4 b (1.675+/-0.241 Jupiter masses) as well as other system and planet parameters. In the transmission spectrum derived from ESPRESSO observations, we resolve excess absorption by H{alpha}, H{beta}, NaI D1&D2, CaII H&K, and a few strong individual lines of MgI, FeI and FeII. We also present the cross-correlation detection of MgI, CaI, CrI, FeI and FeII.

The absorption strength of FeIi significantly exceeds the prediction from a hydrostatic atmospheric model, which is also commonly observed in other UHJs. We attribute this to the presence of FeII in the exosphere as a consequence of hydrodynamic outflows. This is further supported by the positive correlation of absorption strengths of FeII with the H{alpha} line, which is expected to probe the extended upper atmospheres and the mass loss process.

Comparing transmission signatures of various species in the UHJ population allows us to disentangle the hydrostatic regime (as traced via the absorption by MgI and FeI) from the exospheres (as probed by H{alpha} and FeII) of the strongly irradiated atmospheres.