The GTC exoplanet transit spectroscopy survey. V. A spectrally-resolved Rayleigh scattering slope in GJ 3470b
Abstract
Aims: As a sub-Uranus-mass low-density planet, GJ 3470b has been found to show a flat featureless transmission spectrum in the infrared and a tentative Rayleigh scattering slope in the optical. We conducted an optical transmission spectroscopy project to assess the impacts of stellar activity and to determine whether or not GJ 3470b hosts a hydrogen-rich gas envelop.
Methods: We observed three transits with the low-resolution Optical System for Imaging and low-Intermediate-Resolution Integrated Spectroscopy (OSIRIS) at the 10.4 m Gran Telescopio Canarias, and one transit with the high-resolution Ultraviolet and Visual Echelle Spectrograph (UVES) at the 8.2 m Very Large Telescope.
Results: From the high-resolution data, we find that the difference of the Ca II H+K lines in- and out-of-transit is only 0.67 ± 0.22%, and determine a magnetic filling factor of about 10-15%. From the low-resolution data, we present the first optical transmission spectrum in the 435-755 nm band, which shows a slope consistent with Rayleigh scattering.
Conclusions: After exploring the potential impacts of stellar activity in our observations, we confirm that Rayleigh scattering in an extended hydrogen-helium atmosphere is currently the best explanation. Further high-precision observations that simultaneously cover optical and infrared bands are required to answer whether or not clouds and hazes exist at high-altitude.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- April 2017
- DOI:
- 10.1051/0004-6361/201630228
- arXiv:
- arXiv:1703.01817
- Bibcode:
- 2017A&A...600A.138C
- Keywords:
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- planetary systems;
- planets and satellites: individual: GJ 3470b;
- planets and satellites: atmospheres;
- techniques: spectroscopic;
- Astrophysics - Earth and Planetary Astrophysics;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- 12 pages, 11 figures, accepted for publication in A&