Atmospheric characterization of the ultra-hot Jupiter MASCARA-2b/KELT-20b

Abstract

Ultra-hot Jupiters orbit very close to their host star and consequently receive strong irradiation, causing their atmospheric chemistry to be different from the common gas giants. Here, we have studied the atmosphere of one of these particular hot planets, MASCARA-2b/KELT-20b, using four transit observations with high resolution spectroscopy facilities. Three of these observations were performed with HARPS-N and one with CARMENES. Additionally, we simultaneously observed one of the transits with MuSCAT2 to monitor possible spots in the stellar surface. At high resolution, the transmission residuals show the effects of Rossiter-McLaughlin and centre-to-limb variations from the stellar lines profiles, which we have corrected to finally extract the transmission spectra of the planet. We clearly observe the absorption features of CaII, FeII, NaI, Hα, and Hβ in the atmosphere of MASCARA-2b, and indications of Hγ and MgI at low signal-to-noise ratio. In the case of NaI, the true absorption is difficult to disentangle from the strong telluric and interstellar contamination. The results obtained with CARMENES and HARPS-N are consistent, measuring an Hα absorption depth of 0.68 ± 0.05 and 0.59 ± 0.07%, and NaI absorption of 0.11 ± 0.04 and 0.09 ± 0.05% for a 0.75 Å passband, in the two instruments respectively. The Hα absorption corresponds to ~1.2 Rp, which implies an expanded atmosphere, as a result of the gas heating caused by the irradiation received from the host star. For Hβ and Hγ only HARPS-N covers this wavelength range, measuring an absorption depth of 0.28 ± 0.06 and 0.21 ± 0.07%, respectively. For CaII, only CARMENES covers this wavelength range measuring an absorption depth of 0.28 ± 0.05, 0.41 ± 0.05 and 0.27 ± 0.06% for CaII λ8498Å, λ8542Å and λ8662Å lines, respectively. Three additional absorption lines of FeII are observed in the transmission spectrum by HARPS-N (partially covered by CARMENES), measuring an average absorption depth of 0.08 ± 0.04% (0.75 Å passband). The results presented here are consistent with theoretical models of ultra-hot Jupiters atmospheres, suggesting the emergence of an ionised gas on the day-side of such planets. Calcium and iron, together with other elements, are expected to be singly ionised at these temperatures and be more numerous than its neutral state. The Calcium triplet lines are detected here for the first time in transmission in an exoplanet atmosphere.

Detection of Na, K, and Hαabsorption in the atmosphere of WASP-52b using ESPRESSO

“…Phase-resolved high-resolution transmission spectrum can trace the planet motion in radial velocity and thus confirm the origin of the observed excess absorption (e.g., Snellen et al 2010;Casasayas-Barris et al 2019). In our case, the stellar line center, where the planet excess absorption is located (expected to shift between −23 km s −1 and +23 km s −1 , i.e., ∼−0.5 Å to ∼+0.5 Å), is too noisy to exhibit a significant planet trace.…”

“…We used the ESO software molecfit version 1.5.7 Kausch et al 2015) to perform telluric correction, based on a synthetic modeling of the Earth's atmospheric transmission with a line-by-line radiative transfer model. This approach has been adopted in several recent studies of high-resolution transmission spectroscopy (Allart et al 2017(Allart et al , 2018(Allart et al , 2019Nortmann et al 2018;Salz et al 2018;Seidel et al 2019;Casasayas-Barris et al 2019;Hoeijmakers et al 2019;Alonso-Floriano et al 2019;Cauley et al 2019;Cabot et al 2020;Kirk et al 2020). Notes.…”

“…Yan et al 2015Yan et al , 2017Czesla et al 2015;Louden & Wheatley 2015;Cegla et al 2016b). We followed the approach detailed in Casasayas- Barris et al (2019) to generate the CLV+RM model. This approach uses the Spectroscopy Made Easy tool (SME; Valenti & Piskunov 1996;Piskunov & Valenti 2017) to compute the stellar spectra at 21 different angles (µ = cos θ).…”

Detection of neutral atomic species in the ultra-hot Jupiter WASP-121b

“…The effect also averages out for the largest passbands. Minor differences between the observed and modelled CLV and RM effects may be attributed to our LTE assumption (Casasayas-Barris et al 2018); also, we did not account for the effective radius of the planet R λ , which is left as a free parameter in Casasayas- Barris et al (2019). The absorption depths are listed in Table 4.1, and are consistent with the stacked transmission spectrum absorption depths.…”

“…Whereas some previous works construct an empirical telluric model (Wyttenbach et al 2015;Casasayas-Barris et al 2018), we opt to use molecfit for the much lower S/N exposures analyzed here. However, care must be taken to avoid fitting to stellar absorption lines (Allart et al 2017;Hoeijmakers et al 2019;Casasayas-Barris et al 2019). For each exposure, on each night, we shift the DRS wavelength solution to the telescope rest-frame using the Barycentric Earth Radial Velocity (BERV).…”