Publication: CARMENES detection of the Ca II infrared triplet and possible evidence of He I in the atmosphere of WASP-76b
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2021-10-27
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Abstract
Ultra-hot Jupiters are highly irradiated gas giants with equilibrium temperatures typically higher than 2000 K. Atmospheric studies of these planets have shown that their transmission spectra are rich in metal lines, with some of these metals being ionised due to the extreme temperatures. Here, we use two transit observations of WASP-76b obtained with the CARMENES spectrograph to study the atmosphere of this planet using high-resolution transmission spectroscopy. Taking advantage of the two channels and the coverage of the red and near-infrared wavelength ranges by CARMENES, we focus our analysis on the study of the Ca II infrared triplet (IRT) at 8500 A and the He I triplet at 10 830 A. We present the discovery of the Ca II IRT at 7 sigma in the atmosphere of WASP-76b using the cross-correlation technique, which is consistent with previous detections of the Ca II H&K lines in the same planet, and with the atmospheric studies of other ultra-hot Jupiters reported to date. The low mass density of the planet, and our calculations of the XUV (X-ray and EUV) irradiation received by the exoplanet, show that this planet is a potential candidate to have a He I evaporating envelope and, therefore, we performed further investigations focussed on this aspect. The transmission spectrum around the He I triplet shows a broad and red-shifted absorption signal in both transit observations. However, due to the strong telluric contamination around the He I lines and the relatively low signal-to-noise ratio of the observations, we are not able to unambiguously conclude if the absorption is due to the presence of helium in the atmosphere of WASP-76b, and we consider the result to be only an upper limit. Finally, we revisit the transmission spectrum around other lines such as Na I, Li I, H alpha, and K I. The upper limits reported here for these lines are consistent with previous studies.
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ArtĆculo firmado por 28 autores. "We thank the referee for the helpful report, and constructive remarks on this manuscript. CARMENES is an instrument at the Centro AstronĆ³mico Hispano-AlemĆ”n (CAHA) at Calar Alto (Almeria, Spain), operated jointly by the Junta de AndalucĆa and the Instituto de AstrofĆsica de AndalucĆa (CSIC). CARMENES was funded by the Max-Planck-Gesellschaft (MPG), the Consejo Superior de Investigaciones CientĆficas (CSIC), the Ministerio de EconomĆa y Competitividad (MINECO) and the European Regional Development Fund (ERDF) through projects FICTS-2011-02, ICTS-2017-07-CAHA-4, and CAHA16-CE-3978, and the members of the CARMENES Consortium (Max-Planck-Institut fur Astronomie, Instituto de AstrofĆsica de AndalucĆa, Landessternwarte Konigstuhl, Institut de Ciencies de l'Espai, Institut fur Astrophysik Gottingen, Universidad Complutense de Madrid, Thuringer Landessternwarte Tautenburg, Instituto de AstrofĆsica de Canarias, Hamburger Sternwarte, Centro de AstrobiologĆa and Centro AstronĆ³mico Hispano-AlemĆ”n), with additional contributions by the MINECO, the Deutsche Forschungsgemeinschaft through the Major Research Instrumentation Programme and Research Unit FOR2544 "Blue Planets around Red Stars", the Klaus Tschira Stiftung, the states of Baden-Wurttemberg and Niedersachsen, and by the Junta de AndalucĆa. This work was based on data from the CARMENES data archive at CAB (CSIC-INTA). We acknowledge funding from the European Research Council under the European Union's Horizon 2020 research and innovation program under grant agreement no. 694513, the Agencia Estatal de InvestigaciĆ³n of the Ministerio de Ciencia, InnovaciĆ³n y Universidades and the ERDF through projects PID2019-109522GB-C5[1:4]/AEI/10.13039/501100011033, PID2019-110689RB-I00/AEI/10.13039/501100011033, ESP2017-87143-R, and ESP201680435-C2-2-R, and the Centre of Excellence "Severo Ochoa" and "MarĆa de Maeztu" awards to the Instituto de AstrofĆsica de Canarias (CEX2019-000920-S), Instituto de AstrofĆsica de AndalucĆa (SEV-2017-0709), and Centro de AstrobiologĆa (MDM-2017-0737), and the Generalitat de Catalunya/CERCA programme. T.H. acknowledges support by the European Research Council under the Horizon 2020 Framework Program via the ERC Advanced Grant Origins 83 24 28. G.M. has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No. 895525. This work made use of PyAstronomy (Czesla et al. 2019) and of the VALD database, operated at Uppsala University, the Institute of Astronomy RAS in Moscow, and the University of Vienna."