Article (Scientific journals)
WASP-80b has a dayside within the T-dwarf range
Triaud, Amaury H. M. J.; Gillon, Michaël; Ehrenreich, David et al.
2015In Monthly Notices of the Royal Astronomical Society, 450, p. 2279-2290
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Keywords :
planets and satellites: atmospheres; planets and satellites: individual: WASP-80b; binaries: eclipsing; brown dwarfs; Hertzsprung-Russell and colour-magnitude diagrams; stars: late-type
Abstract :
[en] WASP-80b is a missing link in the study of exoatmospheres. It falls between the warm Neptunes and the hot Jupiters and is amenable for characterization, thanks to its host star's properties. We observed the planet through transit and during occultation with Warm Spitzer. Combining our mid-infrared transits with optical time series, we find that the planet presents a transmission spectrum indistinguishable from a horizontal line. In emission, WASP-80b is the intrinsically faintest planet whose dayside flux has been detected in both the 3.6 and 4.5 μm Spitzer channels. The depths of the occultations reveal that WASP-80b is as bright and as red as a T4 dwarf, but that its temperature is cooler. If planets go through the equivalent of an L-T transition, our results would imply that this happens at cooler temperatures than for brown dwarfs. Placing WASP-80b's dayside into a colour-magnitude diagram, it falls exactly at the junction between a blackbody model and the T-dwarf sequence; we cannot discern which of those two interpretations is the more likely. WASP-80b's flux density is as low as GJ 436b at 3.6 μm; the planet's dayside is also fainter, but bluer than HD 189733Ab's nightside (in the [3.6] and [4.5]Spitzer bands). Flux measurements on other planets with similar equilibrium temperatures are required to establish whether irradiated gas giants, such as brown dwarfs, transition between two spectral classes. An eventual detection of methane absorption in transmission would also help lift that degeneracy. We obtained a second series of high-resolution spectra during transit, using HARPS. We reanalyse the Rossiter-McLaughlin effect. The data now favour an aligned orbital solution and a stellar rotation nearly three times slower than stellar line broadening implies. A contribution to stellar line broadening, maybe macroturbulence, is likely to have been underestimated for cool stars, whose rotations have therefore been systematically overestimated.
Disciplines :
Space science, astronomy & astrophysics
Author, co-author :
Triaud, Amaury H. M. J.;  Centre for Planetary Sciences, University of Toronto at Scarborough, 1265 Military Trail, Toronto, ON M1C 1A4, Canada ; Department of Astronomy & Astrophysics, University of Toronto, Toronto, ON M5S 3H4, Canada ; Kavli Institute for Astrophysics & Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
Gillon, Michaël  ;  Université de Liège > Département d'astrophys., géophysique et océanographie (AGO) > Origines Cosmologiques et Astrophysiques (OrCa)
Ehrenreich, David;  Observatoire Astronomique de l'Université de Genève, Chemin des Maillettes 51, CH-1290 Sauverny, Switzerland
Herrero, Enrique;  Institut de Ciències de l'Espai (CSIC-IEEC), Campus UAB, Facultat de Ciències, Torre C5 parell, 2a pl, E-08193 Bellaterra, Spain
Lendl, Monika ;  Université de Liège > Département d'astrophys., géophysique et océanographie (AGO) > Origines Cosmologiques et Astrophysiques (OrCa)
Anderson, David R.;  Astrophysics Group, Keele University, Staffordshire ST5 5BG, UK
Collier Cameron, Andrew;  SUPA, School of Physics & Astronomy, University of St Andrews, North Haugh, St Andrews, Fife KY16 9SS, UK
Delrez, Laetitia ;  Université de Liège > Département d'astrophys., géophysique et océanographie (AGO) > Origines Cosmologiques et Astrophysiques (OrCa)
Demory, Brice-Olivier;  Cavendish Laboratory, J J Thomson Avenue, Cambridge CB3 0HE, UK
Hellier, Coel;  Astrophysics Group, Keele University, Staffordshire ST5 5BG, UK
Heng, Kevin;  Center for Space and Habitability, University of Bern, Sidlerstrasse 5, CH-3012 Bern, Switzerland
Jehin, Emmanuel  ;  Université de Liège > Département d'astrophys., géophysique et océanographie (AGO) > Origines Cosmologiques et Astrophysiques (OrCa)
Maxted, Pierre F. L.;  Astrophysics Group, Keele University, Staffordshire ST5 5BG, UK
Pollacco, Don;  Department of Physics, University of Warwick, Coventry CV4 7AL, UK
Queloz, Didier;  Cavendish Laboratory, J J Thomson Avenue, Cambridge CB3 0HE, UK
Ribas, Ignasi;  Institut de Ciències de l'Espai (CSIC-IEEC), Campus UAB, Facultat de Ciències, Torre C5 parell, 2a pl, E-08193 Bellaterra, Spain
Smalley, Barry;  Astrophysics Group, Keele University, Staffordshire ST5 5BG, UK
Smith, Alexis M. S.;  N. Copernicus Astronomical Centre, Polish Academy of Sciences, Bartycka 18, PL-00-716 Warsaw, Poland
Udry, Stéphane;  Observatoire Astronomique de l'Université de Genève, Chemin des Maillettes 51, CH-1290 Sauverny, Switzerland)
More authors (9 more) Less
Language :
English
Title :
WASP-80b has a dayside within the T-dwarf range
Publication date :
01 July 2015
Journal title :
Monthly Notices of the Royal Astronomical Society
ISSN :
0035-8711
eISSN :
1365-2966
Publisher :
Oxford University Press, Oxford, United Kingdom
Volume :
450
Pages :
2279-2290
Peer reviewed :
Peer Reviewed verified by ORBi
Available on ORBi :
since 01 June 2015

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