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Disentangling the Planet from the Star in Late-Type M Dwarfs: A Case Study of TRAPPIST-1g
Name
Wakeford_2019_AJ_157_11.pdf
Description
Published version
Size
4.28 MB
Format
Adobe PDF
Checksum (MD5)
65884aab2e71bcfe551947ab15e35cb5
Author(s)
Wakeford, HR
Lewis, NK
Fowler, J
Bruno, G
Wilson, TJ
Moran, SE
Valenti, J
Batalha, NE
Filippazzo, J
Bourrier, V
Date Issued
2018
Journal
Astronomical Journal
Publisher
American Astronomical Society
Version
Final published version
Abstract
© 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.
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DOI of Published Version
10.3847/1538-3881/AAF04D
