0 Assigned ID: 169 ----- Attempting Submission 1 (Thu Apr 04 06:13:43 GMT 2019) ----- Starspots pose a major challenge to exoplanet transmission spectroscopy observations. Spots break our common simplifying assumption that a transiting planet blocks light along a chord whose spectrum is representative of the star as whole. They can therefore cause the apparent transit depth of the planet to vary with wavelength. Spots can be a particularly egregious problem for cool stars, where water features in the spotted stellar photosphere can introduce spurious features that are easily mistaken for water absorption in a planet's transmission spectrum. Here, we propose an archival investigation aimed at constructing an accurate probabilistic model for this troublesome "transit light source effect" by shining new light on the complicated photospheres of cool stars. For M dwarf exoplanet host stars observed by WFC3, we will recycle archival out-of-transit spectra into long-term spectrophotometric light curves sensitive to spots rotating in and out of view on the star. By directly measuring the way a rotating starspot modulates the stellar spectrum, we hope to construct more accurate predictive models for the effect of starspots on transit depths and therefore enable more reliable retrievals of the properties of transiting exoplanet atmospheres. The transit light source effect will be increasingly relevant for transmission spectroscopy in the JWST era. The methodological approach taken in this project would potentially also be applicable to multi-visit transmission spectroscopy observations with JWST, providing an avenue to mitigate this persnickety problem. Prof. Zach Berta-Thompson has expertise with HST observations, WFC3 data reduction, transiting exoplanet spectrophotometry, and the interpretation of M dwarf planetary systems. Dr. Michael Gully-Santiago has expertise in constructing detailed models of spotted stellar photospheres and performing reliable inferences from complicated datasets. Prof. Caroline Morley has expertise with the theory of exoplanet atmospheres and has developed well-trusted models for exoplanet transmission spectroscopy. Prof. Elisabeth Newton has expertise with observations of cool stars from both the ground and space, with a particular focus on M dwarf photometric modulations caused by rotating starspots. Collectively, the team members have served as PIs on eight accepted Hubble GO or AR projects, and they have contributed as Co-I in numerous others. Planets and Planet Formation Stellar Physics 0 Regular false false false false false SUPPORTED