Detection of water absorption in the day side atmosphere of HD 189733 b using ground-based high-resolution spectroscopy at 3.2μm

J. L. Birkby*, R. J. de Kok, M. Brogi, E. J.W. de Mooij, H. Schwarz, S. Albrecht, I. A.G. Snellen

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

245 Citations (Scopus)


We report a 4.8σ detection of water absorption features in the day side spectrum of the hot Jupiter HD 189733 b. We used high-resolution (R ~ 100 000) spectra taken at 3.2 μm with CRIRES on the VLT to trace the radial-velocity shift of the water features in the planet's day side atmosphere during 5 h of its 2.2 d orbit as it approached secondary eclipse. Despite considerable telluric contamination in this wavelength regime, we detect the signal within our uncertainties at the expected combination of systemic velocity (Vsys = -3+5-6 km s-1) and planet orbital velocity (Kp = 154+14-10 km s-1), and determine a H2O line contrast ratio of (1.3± 0.2) × 10-3 with respect to the stellar continuum. We find no evidence of significant absorption or emission from other carbon-bearing molecules, such as methane, although we do note a marginal increase in the significance of our detection to 5.1σ with the inclusion of carbon dioxide in our template spectrum. This result demonstrates that ground-based, highresolution spectroscopy is suited to finding not just simple molecules like CO, but also to more complex molecules like H2O even in highly telluric contaminated regions of the Earth's transmission spectrum. It is a powerful tool that can be used for conducting an immediate census of the carbon- and oxygen-bearing molecules in the atmospheres of giant planets, and will potentially allow the formation and migration history of these planets to be constrained by the measurement of their atmospheric C/O ratios.

Original languageEnglish
Pages (from-to)L35-L39
JournalMonthly Notices of the Royal Astronomical Society: Letters
Issue number1
Publication statusPublished - 01 Nov 2013
Externally publishedYes


  • Planetary systems
  • Stars: individual: hd 189733
  • Techniques: spectroscopic

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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