ACCESS I. AN OPTICAL TRANSMISSION SPECTRUM of GJ 1214b REVEALS A HETEROGENEOUS STELLAR PHOTOSPHERE

Benjamin Rackham, Néstor Espinoza, Dániel Apai, Mercedes López-Morales, Andrés Jordán, David J. Osip, Nikole K. Lewis, Florian Rodler, Jonathan D. Fraine, Caroline V. Morley, Jonathan J. Fortney

Research output: Contribution to journalArticle

21 Scopus citations

Abstract

GJ 1214b is the most studied sub-Neptune exoplanet to date. Recent measurements have shown its near-infrared transmission spectrum to be flat, pointing to a high-altitude opacity source in the exoplanet's atmosphere, either equilibrium condensate clouds or photochemical hazes. Many photometric observations have been reported in the optical by different groups, though simultaneous measurements spanning the entire optical regime are lacking. We present an optical transmission spectrum (4500-9260 of GJ 1214b in 14 bins, measured with Magellan/IMACS repeatedly over three transits. We measure a mean planet-to-star radius ratio of and mean uncertainty of in the spectral bins. The optical transit depths are shallower on average than observed in the near-infrared. We present a model for jointly incorporating the effects of a composite photosphere and atmospheric transmission through the exoplanet's limb (the CPAT model), and use it to examine the cases of absorber and temperature heterogeneities in the stellar photosphere. We find the optical and near-infrared measurements are best explained by the combination of (1) photochemical haze in the exoplanetary atmosphere with a mode particle size r = 0.1 μm and haze-forming efficiency and (2) faculae in the unocculted stellar disk with a temperature contrast K, assuming 3.2% surface coverage. The CPAT model can be used to assess potential contributions of heterogeneous stellar photospheres to observations of exoplanet transmission spectra, which will be important for searches for spectral features in the optical.

Original languageEnglish (US)
Article number151
JournalAstrophysical Journal
Volume834
Issue number2
DOIs
StatePublished - Jan 10 2017

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Keywords

  • methods: observational
  • planets and satellites: atmospheres
  • planets and satellites: individual (GJ 1214b)
  • stars: activity
  • techniques: spectroscopic

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Rackham, B., Espinoza, N., Apai, D., López-Morales, M., Jordán, A., Osip, D. J., Lewis, N. K., Rodler, F., Fraine, J. D., Morley, C. V., & Fortney, J. J. (2017). ACCESS I. AN OPTICAL TRANSMISSION SPECTRUM of GJ 1214b REVEALS A HETEROGENEOUS STELLAR PHOTOSPHERE. Astrophysical Journal, 834(2), [151]. https://doi.org/10.1088/1361-6560/aa4f6c