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

Abstract

WASP-52b is a low density hot Jupiter orbiting a moderately active K2V star. Previous low-resolution studies have revealed a cloudy atmosphere and found atomic Na above the cloud deck. Here we report the detection of excess absorption at the Na doublet, the Hα line, and the K D 1 line. We derived a high-resolution transmission spectrum based on three transits of WASP-52b, observed with the ultra stable, high-resolution spectrograph ESPRESSO at the VLT. We measure a line contrast of 1.09 ± 0.16% for Na D 1 , 1.31 ± 0.13% for Na D 2 , 0.86 ± 0.13% for Hα, and 0.46 ± 0.13% for K D 1 , with a line FWHM range of 11-22 km s −1 . We also find that the velocity shift of these detected lines during the transit is consistent with the planet orbital motion, thus confirming their planetary origin. We do not observe any significant net blueshift or redshift that can be attributed to planetary winds. We use activity indicator lines as control but find no excess absorption. However, we do notice signatures arising from the Center-to-Limb variation (CLV) and the Rossiter-McLaughlin (RM) effect at these control lines. This highlights the importance of the CLV+RM correction in correctly deriving the transmission spectrum, which, if not corrected, could resemble or cancel out planetary absorption in certain cases. WASP-52b is the second non-ultra-hot Jupiter to show excess Hα absorption, after HD 189733b. Future observations targeting non-ultra-hot Jupiters that show Hα could help reveal the relation between stellar activity and the heating processes in the planetary upper atmosphere.

Mass-loss rate and local thermodynamic state of the KELT-9 b thermosphere from the hydrogen Balmer series

“…Our work shows that with the infrared metastable Helium triplet (λ10830 Å, Seager & Sasselov 2000;Oklopčić & Hirata 2018;Spake et al 2018;Allart et al 2018;Nortmann et al 2018), the Balmer series is an alternative new tool for probing exoplanet evaporation, alongside with classical UV observations (Vidal-Madjar et al 2003). Furthermore, these two probes seems to be complementary since the helium lines are mainly sensitive to G and K-type exoplanetary systems (Oklopčić 2019), while the Balmer lines are more sensitive to early-type (A-type to Gtype) systems (Jensen et al 2012(Jensen et al , 2018Yan & Henning 2018;Casasayas-Barris et al 2018, 2019Cabot et al 2020;Chen et al 2020). Finally, such observations will benefit from the ESPRESSO spectrograph (Pepe et al 2013(Pepe et al , 2014).…”

“…Finally, such observations will benefit from the ESPRESSO spectrograph (Pepe et al 2013(Pepe et al , 2014). On the one hand, ESPRESSO will increase the S/N of the absorption lines (Ehrenreich et al 2020;Chen et al 2020). On the other hand, in combination with near-infrared spectrographs (CARMENES, SPIRou, NIRPS), it will be possible to detect more absorption lines arising from different electronic levels of a given atomic species.…”

“…Indeed, the additional detections of Hα by Yan & Henning (2018); Turner et al (2020), and of Hα, Hβ by Cauley et al (2019), also bring in important clues about the KELT-9 system because measuring absorption from specific strong opacity lines, such as the sodium Na I D doublet or the hydrogen Balmer lines, allow us to probe higher layers ( 1.2 planetary radii) in the thermosphere (Christie et al 2013;Heng et al 2015;Huang et al 2017). So far Hα has only been observed in six exoplanets, four of which are classed as ultra-hot Jupiters (Jensen et al 2012(Jensen et al , 2018Cauley et al 2015Cauley et al , 2016Cauley et al , 2017aCauley et al ,b,c, 2019Barnes et al 2016;Casasayas-Barris et al 2018, 2019Cabot et al 2020;Chen et al 2020). The detection of an optically thick Hα absorption in the atmosphere of KELT-9 b, which takes place at up to ∼1.6 planetary radii (at ∼10 000 K in the thermosphere), provides hints that the hydrogen is filling up the planetary Roche lobe (1.95 R p ) and is escaping from the planet at a rate of ∼10 12 g s −1 .…”

“…achieved with sodium detections (Charbonneau et al 2002;Redfield et al 2008;Snellen et al 2008). Recent results suggest that high-resolution (typically λ/∆λ ∼ 10 5 ) transmission spectra of hot Jupiters probe their thermospheres, a key region of the upper atmosphere, in order to understand irradiated planets and allow us to achieve precise temperature and wind measurements because the lines (e.g., the Na I D doublet, the K I D doublet, the H I Balmer lines Hα, β, γ, the He I (2 3 S) triplet) are resolved and studies benefit from large signals (e.g., Wyttenbach et al 2015Wyttenbach et al , 2017Casasayas-Barris et al 2017, 2019Khalafinejad et al 2017Khalafinejad et al , 2018Seidel et al 2019;Yan & Henning 2018;Cauley et al 2019;Allart et al 2018Allart et al , 2019Nortmann et al 2018;Salz et al 2018;Alonso-Floriano et al 2019;Keles et al 2019;Chen et al 2020). Another landmark achievement obtained in the optical domain is the detection, with cross-correlation, of iron and other metals in the atmosphere of several ultra-hot Jupiters (Hoeijmakers et al 2018(Hoeijmakers et al , 2019Borsa et al 2019;Bourrier et al 2020a;Cabot et al 2020;Gibson et al 2020;Nugroho et al 2020;Stangret et al 2020;Ehrenreich et al 2020).…”

Constraints on Metastable Helium in the Atmospheres of WASP-69b and WASP-52b with Ultranarrowband Photometry

“…high-resolution spectrograph on the Very Large Telescope (Chen et al 2020). Though its host star is relatively faint, WASP-52b is well worth additional observations in metastable helium, as the other detected atomic species will provide some context for modeling the upper atmosphere of this planet.…”