The Transit Light Source Effect: False Spectral Features and Incorrect Densities for M-dwarf Transiting Planets
AffiliationUniv Arizona, Steward Observ, Dept Astron
Univ Arizona, Dept Planetary Sci
planets and satellites: atmospheres
planets and satellites: fundamental parameters
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PublisherIOP PUBLISHING LTD
CitationThe Transit Light Source Effect: False Spectral Features and Incorrect Densities for M-dwarf Transiting Planets 2018, 853 (2):122 The Astrophysical Journal
JournalThe Astrophysical Journal
Rights© 2018. The American Astronomical Society. All rights reserved.
Collection InformationThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at firstname.lastname@example.org.
AbstractTransmission spectra are differential measurements that utilize stellar illumination to probe transiting exoplanet atmospheres. Any spectral difference between the illuminating light source and the disk-integrated stellar spectrum due to starspots and faculae will be imprinted in the observed transmission spectrum. However,. few constraints exist for the extent of photospheric heterogeneities in M dwarfs. Here we model spot and faculae covering fractions consistent with observed photometric variabilities for M dwarfs and the associated 0.3-5.5. mu m stellar contamination spectra. We find that large ranges of spot and faculae covering fractions are consistent with observations and corrections assuming a linear relation between variability amplitude, and covering fractions generally underestimate the stellar contamination. Using realistic estimates for spot and faculae covering fractions, we find that stellar contamination can be more than 10x. larger than the transit depth changes expected for atmospheric features in rocky exoplanets. We also find that stellar spectral contamination can lead to systematic errors in radius and therefore the derived density of small planets. In the case of the TRAPPIST-1 system, we show that TRAPPIST-1 ' s rotational variability is consistent with spot covering fractions f(spot) = 8(7)(+18)% and faculae covering fractions f(fac) = 54(-46)(+16)%. The associated stellar contamination signals alter the transit depths of the TRAPPIST-1 planets at wavelengths of interest for planetary atmospheric species by roughly 1-15x. the strength of planetary features, significantly complicating JWST follow-up observations of this system. Similarly, we find that stellar contamination can lead to underestimates of the bulk densities of the TRAPPIST-1 planets of Delta(rho) = -8(-20)(+7)%, thus leading to overestimates of their volatile contents.
VersionFinal published version
SponsorsNational Science Foundation Graduate Research Fellowship Program [DGE-1143953]; Max Planck Institute for Astronomy, Heidelberg; NASA's Science Mission Directorate