Access: A featureless optical transmission spectrum for WASP-19b from Magellan/IMACS

Néstor Espinoza, Benjamin V. Rackham, Andrés Jordán, Dániel Apai, Mercedes López-Morales, David J. Osip, Simon L. Grimm, Jens Hoeijmakers, Paul A. Wilson, Alex Bixel, Chima McGruder, Florian Rodler, Ian Weaver, Nikole K. Lewis, Jonathan J. Fortney, Jonathan Fraine

Research output: Contribution to journalArticlepeer-review

95 Scopus citations


The short-period (0.94-d) transiting exoplanet WASP-19b is an exceptional target for transmission spectroscopy studies, due to its relatively large atmospheric scale height (∼500 km) and equilibrium temperature (∼2100 K). Here, we report on six precise spectroscopic Magellan/IMACS observations, five of which target the full optical window from 0.45 to 0.9 μm and one targeting the 0.4-0.55 μm blue-optical range. Five of these data sets are consistent with a transmission spectrum without any significant spectral features, while one shows a significant slope as a function of wavelength, which we interpret as arising from photospheric heterogeneities in the star. Coupled with HST/WFC3 infrared observations, our optical/near-infrared measurements point to the presence of high altitude clouds in WASP-19b's atmosphere in agreement with previous studies. Using a semi-analytical retrieval approach, considering both planetary and stellar spectral features, we find a water abundance consistent with solar for WASP-19b and strong evidence for sub-solar abundances for optical absorbers such as TiO and Na; no strong optical slope is detected, which suggests that if hazes are present, they are much weaker than previously suggested. In addition, two spot-crossing events are observed in our data sets and analysed, including one of the first unambiguously detected bright-spot-crossing events on an exoplanet host star.

Original languageEnglish
Pages (from-to)2065-2087
Number of pages23
JournalMonthly Notices of the Royal Astronomical Society
Issue number2
StatePublished - 11 Jan 2019
Externally publishedYes


  • Planets and satellites: atmospheres
  • Planets and satellites: individual: WASP-19b
  • Stars: activit
  • Stars: individual: WASP-19
  • Starspots
  • Techniques: spectroscopic


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