Hot Exoplanet Atmospheres Resolved with Transit Spectroscopy (HEARTS). I. Detection of hot neutral sodium at high altitudes on WASP-49b

Journal
Date Issued
2017
Author(s)
Wyttenbach, A.
•
Lovis, C.
•
Ehrenreich, D.
•
Bourrier, V.
•
•
Allart, R.
•
Astudillo-Defru, N.
•
Cegla, H. M.
•
Heng, K.
•
Lavie, B.
•
Melo, C.
•
Murgas, F.
•
Santerne, A.
•
Ségransan, D.
•
Udry, S.
•
Pepe, F.
DOI
Abstract
High-resolution optical spectroscopy during the transit of HD 189733b, a prototypical hot Jupiter, allowed the resolution of the Na I D sodium lines in the planet, giving access to the extreme conditions of the planet upper atmosphere. We have undertaken HEARTS, a spectroscopic survey of exoplanet upper atmospheres, to perform a comparative study of hot gas giants and determine how stellar irradiation affect them. Here, we report on the first HEARTS observations of the hot Saturn-mass planet WASP-49b. We observed the planet with the HARPS high-resolution spectrograph at ESO 3.6 m telescope. We collected 126 spectra of WASP-49, covering three transits of WASP-49b. We analyzed and modeled the planet transit spectrum, while paying particular attention to the treatment of potentially spurious signals of stellar origin. We spectrally resolve the Na I D lines in the planet atmosphere and show that these signatures are unlikely to arise from stellar contamination. The large contrasts of 2.0 ± 0.5% (D2) and 1.8 ± 0.7% (D1) require the presence of hot neutral sodium ( K) at high altitudes ( 1.5 planet radius or 45 000 km). From estimating the cloudiness index of WASP-49b, we determine its atmosphere to be cloud free at the altitudes probed by the sodium lines. WASP-49b is close to the border of the evaporation desert and exhibits an enhanced thermospheric signature with respect to a farther-away planet such as HD 189733b.

Based on observations made at ESO 3.6 m telescope at the La Silla Observatory under ESO program 096.C-0331....

Volume
602
Start page
A36
Uri
Url
Issn Identifier
0004-6361
Ads BibCode
2017A&A...602A..36W
Rights
open.access
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