Disentangling the Planet from the Star in Late-Type M Dwarfs: A Case Study of TRAPPIST-1g
Author(s)
Wakeford, HR; Lewis, NK; Fowler, J; Bruno, G; Wilson, TJ; Moran, SE; Valenti, J; Batalha, NE; Filippazzo, J; Bourrier, V; Hörst, SM; Lederer, SM; de Wit, J; ... Show more Show less
DownloadPublished version (4.281Mb)
Publisher Policy
Publisher Policy
Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use.
Terms of use
Metadata
Show full item recordAbstract
© 2018. The American Astronomical Society. All rights reserved. The atmospheres of late M stars represent a significant challenge in the characterization of any transiting exoplanets because of the presence of strong molecular features in the stellar atmosphere. TRAPPIST-1 is an ultracool dwarf, host to seven transiting planets, and contains its own molecular signatures that can potentially be imprinted on planetary transit lightcurves as a result of inhomogeneities in the occulted stellar photosphere. We present a case study on TRAPPIST-1g, the largest planet in the system, using a new observation together with previous data, to disentangle the atmospheric transmission of the planet from that of the star. We use the out-of-transit stellar spectra to reconstruct the stellar flux on the basis of one, two, and three temperature components. We find that TRAPPIST-1 is a 0.08 M ∗, 0.117 R ∗, M8V star with a photospheric effective temperature of 2400 K, with ∼35% 3000 K spot coverage and a very small fraction, <3%, of ∼5800 K hot spot. We calculate a planetary radius for TRAPPIST-1g to be R p = 1.124 R ⊕with a planetary density of ρ p = 0.8214 ρ ⊕. On the basis of the stellar reconstruction, there are 11 plausible scenarios for the combined stellar photosphere and planet transit geometry; in our analysis, we are able to rule out eight of the 11 scenarios. Using planetary models, we evaluate the remaining scenarios with respect to the transmission spectrum of TRAPPIST-1g. We conclude that the planetary transmission spectrum is likely not contaminated by any stellar spectral features and are able to rule out a clear solar H2/He-dominated atmosphere at greater than 3σ.
Date issued
2018-12Department
Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary SciencesJournal
Astronomical Journal
Publisher
American Astronomical Society
ISSN
1538-3881