Journal
ASTRONOMY & ASTROPHYSICS
Volume 602, Issue -, Pages -Publisher
EDP SCIENCES S A
DOI: 10.1051/0004-6361/201630063
Keywords
planets and satellites: atmospheres; planets and satellites: individual: WASP-49b; techniques: spectroscopic; instrumentation: spectrographs; methods: observational
Categories
Funding
- Swiss National Science Foundation (SNSF)
- SNSF [200020_152721, 200020_166227]
- Swiss National Science Foundation (SNF) [200020_152721, 200020_166227] Funding Source: Swiss National Science Foundation (SNF)
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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% (D-2) and 1.8 +/- 0.7% (D-1) require the presence of hot neutral sodium (2950(-500)(+400) K) at high altitudes (similar to 1.5 planet radius or similar to 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.
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