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WASP-80b has a dayside within the T-dwarf range

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MNRAS_2015_Triaud_2279_90.pdf (2.588Mb)
Date
01/07/2015
Author
Triaud, Amaury H. M. J.
Gillon, Michael
Ehrenreich, David
Herrero, Enrique
Lendl, Monika
Anderson, David R.
Cameron, Andrew Collier
Delrez, Laetitia
Demory, Brice-Olivier
Hellier, Coel
Heng, Keving
Jehin, Emmanuel
Maxted, Pierre F. L.
Pollacco, Don
Queloz, Didier
Ribas, Ignasi
Smalley, Barry
Smith, Alexis Michael Sheridan
Udry, Stephane
Keywords
Planets and satellites: atmospheres
Planets and satellites: individual: WASP-80b
Binaries: eclipsing
Brown dwarfs
Hertzsprung–Russell and colour–magnitude diagrams
Stars: late-type
QB Astronomy
QC Physics
DAS
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Abstract
WASP-80b is a missing link in the study of exo-atmospheres. It falls between the warm Neptunes and the hot Jupiters and is amenable for characterisation, 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 $\mu$m 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 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. Flux measurements on other planets with similar equilibrium temperatures are required to establish whether irradiated gas giants, like 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. [abridged]
Citation
Triaud , A H M J , Gillon , M , Ehrenreich , D , Herrero , E , Lendl , M , Anderson , D R , Cameron , A C , Delrez , L , Demory , B-O , Hellier , C , Heng , K , Jehin , E , Maxted , P F L , Pollacco , D , Queloz , D , Ribas , I , Smalley , B , Smith , A M S & Udry , S 2015 , ' WASP-80b has a dayside within the T-dwarf range ' , Monthly Notices of the Royal Astronomical Society , vol. 450 , no. 3 , pp. 2279-2290 . https://doi.org/10.1093/mnras/stv706
Publication
Monthly Notices of the Royal Astronomical Society
Status
Peer reviewed
DOI
https://doi.org/10.1093/mnras/stv706
ISSN
0035-8711
Type
Journal article
Rights
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society. © 2015 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society All rights reserved.
Description
AHMJT is a Swiss National Science Foundation (SNSF) fellow under grant number P300P2-147773. MG and EJ are Research Associates at the F.R.S-FNRS; LD received the support the support of the F.R.I.A. fund of the FNRS. DE, KH, and SU acknowledge the financial support of the SNSF in the frame of the National Centre for Competence in Research ‘PlanetS’. EH and IR acknowledge support from the Spanish Ministry of Economy and Competitiveness (MINECO) and the ‘Fondo Europeo de Desarrollo Regional’ (FEDER) through grants AYA2012-39612-C03-01 and ESP2013-48391-C4-1-R.
Collections
  • University of St Andrews Research
URL
http://mnras.oxfordjournals.org/content/450/3/2279/suppl/DC1
URI
http://hdl.handle.net/10023/7458

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