Publication: He I λ 10 830 Å in the transmission spectrum of HD 209458 b
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2019-09
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Abstract
Context. Recently, the He I triplet at 10 830 Å was rediscovered as an excellent probe of the extended and possibly evaporating atmospheres of close-in transiting planets. This has already resulted in detections of this triplet in the atmospheres of a handful of planets, both from space and from the ground. However, while a strong signal is expected for the hot Jupiter HD 209458 b, only upper limits have been obtained so far.
Aims. Our goal is to measure the helium excess absorption from HD 209458 b and assess the extended atmosphere of the planet and possible evaporation.
Methods. We obtained new high-resolution spectral transit time-series of HD 209458 b using CARMENES at the 3.5 m Calar Alto telescope, targeting the He I triplet at 10 830 Å at a spectral resolving power of 80 400. The observed spectra were corrected for stellar absorption lines using out-of-transit data, for telluric absorption using the MOLECFIT software, and for the sky emission lines using simultaneous sky measurements through a second fibre.
Results. We detect He I absorption at a level of 0.91 ± 0.10% (9σ) at mid-transit. The absorption follows the radial velocity change of the planet during transit, unambiguously identifying the planet as the source of the absorption. The core of the absorption exhibits a net blueshift of 1.8 ± 1.3 km s^(−1) . Possible low-level excess absorption is seen further blueward from the main absorption near the centre of the transit, which could be caused by an extended tail. However, this needs to be confirmed. Conclusions. Our results further support a close relation between the strength of planetary absorption in the helium triplet lines and the level of ionising, stellar X-ray, and extreme-UV irradiation.
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© ESO 2019. Artículo firmado por 30 autores. We thank P. Mollière and A. Wyttenbach for the nice scientific discussions during the preparation of this publication. F.J.A.-F. and I.S. acknowledge funding from the European Research Council (ERC) under the European Union Horizon 2020 research and innovation programme under grant agreement No 694 513. CARMENES is funded by the German MaxPlanck-Gesellschaft (MPG), the Spanish Consejo Superior de Investigaciones Científicas (CSIC), the European Union through FEDER/ERF FICTS-2011-02 funds, and the members of the CARMENES Consortium (MaxPlanck-Institut für Astronomie, Instituto de Astrofísica de Andalucía, Landessternwarte Königstuhl, Institut de Ciències de l’Espai, Institut für Astrophysik Göttingen, Universidad Complutense de Madrid, Thüringer Landessternwarte Tautenburg, Instituto de Astrofísica de Canarias, Hamburger Sternwarte, Centro de Astrobiología and Centro Astronómico Hispano-Alemán), with additional contributions by the Spanish Ministry of Economy, the German Science Foundation through the Major Research Instrumentation Programme and DFG Research Unit FOR2544 “Blue Planets around Red Stars”, the Klaus Tschira Stiftung, the states of Baden-Württemberg and Niedersachsen, and by the Junta de Andalucía. Financial support was also provided by the Universidad Complutense de Madrid, the Comunidad Autónoma de Madrid, the Spanish Ministerios de Ciencia e Innovación and of Economía y Competitividad, the State Agency for Research of the Spanish MCIU through the “Center of Excellence Severo Ochoa” and Science & Technology Facility Council Consolidated, and the Fondo Social Europeo. The corresponding funding grants are: ESP2014–54 362–P, ESP2014–54 062–R, AYA2015-69 350–C3–2–P, BES–2015–074542, AYA2016- 79 425–C3–1/2/3–P, ESP2016–76 076–R, ESP2017–87 143–R, SEV–2017–0709, ST/P000592/1. Based on observations collected at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated jointly by the Max–Planck Institut für Astronomie and the Instituto de Astrofísica de Andalucía. We thank the anonymous referee for their insightful comments, which contributed to improve the quality of the manuscript.