We report the detection of water absorption features in the dayside spectrum of the first-known hot Jupiter, 51 Peg b, confirming the star-planet system to be a double-lined spectroscopic binary.
We used high-resolution (R~100,000), 3.2 micron spectra taken with CRIRES/VLT to trace the radial-velocity shift of the water features in the planet’s dayside atmosphere during 4 hours of its 4.23-day orbit after superior conjunction. We detect the signature of molecular absorption by water at a significance of 5.6 sigma at a systemic velocity of Vsys=-33+/-2 km/s, coincident with the host star, with a corresponding orbital velocity Kp = 133^+4.3_-3.5 km/s. This translates directly to a planet mass of Mp=0.476^+0.032_-0.031MJ, placing it at the transition boundary between Jovian and Neptunian worlds. We determine upper and lower limits on the orbital inclination of the system of 70
We find no evidence of significant absorption or emission from other major carbon-bearing molecules of the planet, including methane and carbon dioxide. The atmosphere is non-inverted in the temperature-pressure region probed by these observations. The deepest absorption lines reach an observed relative contrast of 0.9×10^-3 with respect to the host star continuum flux, at an angular separation of 3 milliarcseconds. This work is consistent with a previous tentative report of K-band molecular absorption for 51 Peg b by Brogi et al. (2013).
J. L. Birkby, R. J. de Kok, M. Brogi, H. Schwarz, I. A. G. Snellen
(Submitted on 25 Jan 2017)
Comments: 20 pages, 14 figures. Table 1 is available in full in the arXiv source file. Accepted for publication in The Astronomical Journal
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:1701.07257 [astro-ph.EP] (or arXiv:1701.07257v1 [astro-ph.EP] for this version)
From: Jayne Birkby
[v1] Wed, 25 Jan 2017 10:47:14 GMT (2213kb,D)
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