Investigation of the upper atmosphere in ultra-hot Jupiter WASP-76 b with high-resolution spectroscopy

Abstract

Alkali metal lines are one of the most important key opacity sources for understanding exoplanetary atmospheres because the Na I resonance doublets are thought to be the cause of low albedo, as the alkali metal's wide line wings absorb almost all of the incoming stellar irradiation. High-resolution transmission spectroscopy of Na absorption lines can be used to investigate the temperature of the thermosphere of hot Jupiters, which is increased by stellar X-ray and EUV irradiation. We applied high-resolution transmission spectroscopy to the ultrahot Jupiter WASP-76 b with the High Dispersion Spectrograph (HDS) on the Subaru 8.2 m telescope. We report the detection of strong Na D excess absorption with line contrasts of 0.42 ± 0.03 % (D1 at 5895.92 Å) and 0.38 ± 0.04 % (D2 at 5889.95 Å), FWHMs of 1.63 ± 0.13 Å (D1) and 1.87 ± 0.22 Å (D2), and EWs of (7.29 ± 1.43) × 10 −3 Å (D1) and (7.56 ± 2.38) × 10 −3 Å (D2). These results show that the Na D absorption lines are shallower and broader than those in previous work, whereas the absorption signals over the same passband are consistent with those in previous work. We derive the best-fitted isothermal temperature of 3700 K (without rotation) and 4200 K (with rotation). These results suggest the possibility of the existence of a thermosphere because the derived atmospheric temperature is higher than the equilibrium temperature (∼ 2160 K).

Magnetic Drag and 3-D Effects in Theoretical High-Resolution Emission Spectra of Ultrahot Jupiters: the Case of WASP-76b

“…Our models are all based on parameters from the UHJ WASP-76b, an inflated planet orbiting its host star every 1.81 days. This planet has been the target of many high-resolution transit analyses, and a multitude of different species have been detected in its atmosphere, including Fe I, Na, Li I, Ca II (Seidel et al 2019;Deibert et al 2021;Casasayas-Barris et al 2021;Kawauchi et al 2021;Tabernero et al 2021), and recently molecules like OH (Landman et al 2021).Analyses of high resolution emission spectra have yet to be published. The work by Kesseli et al (2021) explores an entire atomic spectral survey of the atoms and ions that have been detected on this UHJ and finds evidence for temperature and chemical gradients on the planet.…”