High-resolution transmission spectroscopy of MASCARA-2 b with EXPRES

H. Jens Hoeijmakers*, Samuel H.C. Cabot, Lily Zhao, Lars A. Buchhave, Rene Tronsgaard, Allen B. Davis, Daniel Kitzmann, Simon L. Grimm, Heather M. Cegla, Vincent Bourrier, David Ehrenreich, Kevin Heng, Christophe Lovis, Debra A. Fischer

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review


We report detections of atomic species in the atmosphere of MASCARA-2 b, using the first transit observations obtained with the newly commissioned EXPRES spectrograph. EXPRES is a highly stabilized optical echelle spectrograph, designed to detect stellar reflex motions with amplitudes down to 30 cm s-1, and has recently been deployed at the Lowell Discovery Telescope. By analyzing the transmission spectrum of the ultra-hot Jupiter MASCARA-2 b using the cross-correlation method, we confirm previous detections of Fe※ I, Fe※ II, and Na※ I, which likely originate in the upper regions of the inflated atmosphere. In addition, we report significant detections of Mg※ I and Cr※ II. The absorption strengths change slightly with time, possibly indicating different temperatures and chemistry in the day- and nightside terminators. Using the effective stellar line-shape variation induced by the transiting planet, we constrain the projected spin-orbit misalignment of the system to 1.6 ± 3.1 degrees, consistent with an aligned orbit. We demonstrate that EXPRES joins a suite of instruments capable of phase-resolved spectroscopy of exoplanet atmospheres.
Original languageEnglish
Article numberA120
JournalAstronomy and Astrophysics
Number of pages17
Publication statusPublished - 2020


  • Instrumentation: spectrographs
  • Planets and satellites: atmospheres
  • Techniques: spectroscopic
  • Planets and satellites: gaseous planets

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