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Non-detection of L-band Line Emission from the Exoplanet HD189733b

Mandell, Avi M. and Deming, L. Drake and Blake, Geoffrey A. and Knutson, Heather A. and Mumma, Michael J. and Villanueva, Geronimo L. and Salyk, Colette (2011) Non-detection of L-band Line Emission from the Exoplanet HD189733b. Astrophysical Journal, 728 (1). Art. No. 18. ISSN 0004-637X.

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We attempt to confirm bright non-local thermodynamic equilibrium (non-LTE) emission from the exoplanet HD 189733b at 3.25 μm, as recently reported by Swain et al. based on observations at low spectral resolving power (λ/δλ ≈ 30). Non-LTE emission lines from gas in an exoplanet atmosphere will not be significantly broadened by collisions, so the measured emission intensity per resolution element must be substantially brighter when observed at high spectral resolving power. We observed the planet before, during, and after a secondary eclipse event at a resolving power λ/δλ = 27, 000 using the NIRSPEC spectrometer on the Keck II telescope. Our spectra cover a spectral window near the peak found by Swain et al., and we compare emission cases that could account for the magnitude and wavelength dependence of the Swain et al. result with our final spectral residuals. To model the expected line emission, we use a general non-equilibrium formulation to synthesize emission features from all plausible molecules that emit in this spectral region. In every case, we detect no line emission to a high degree of confidence. After considering possible explanations for the Swain et al. results and the disparity with our own data, we conclude that an astrophysical source for the putative non-LTE emission is unlikely. We note that the wavelength dependence of the signal seen by Swain et al. closely matches the 2ν_2 band of water vapor at 300 K, and we suggest that an imperfect correction for telluric water is the source of the feature claimed by Swain et al.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Mandell, Avi M.0000-0002-8119-3355
Deming, L. Drake0000-0001-5727-4094
Blake, Geoffrey A.0000-0003-0787-1610
Knutson, Heather A.0000-0002-0822-3095
Salyk, Colette0000-0003-3682-6632
Additional Information:© 2011 American Astronomical Society. Received 2010 May 27; accepted 2010 November 22; published 2011 January 14. This research was supported by the Goddard Center for strobiology and the NASA Post-doctoral Fellowship Program. The data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation. The authors recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community.We are most fortunate to have the opportunity to conduct observations from this mountain. We also thank the anonymous referee for constructive comments. Facilities: Keck:II (NIRSPEC)
Funding AgencyGrant Number
Goddard Center for AstrobiologyUNSPECIFIED
NASA Postdoctoral ProgramUNSPECIFIED
W. M. Keck FoundationUNSPECIFIED
Subject Keywords:astrobiology; infrared: planetary systems; planets and satellites: individual (HD189733b); radiative transfer; techniques: spectroscopic
Issue or Number:1
Classification Code:PACS: 97.82.-j; 95.30.Gv; 95.30.Ky
Record Number:CaltechAUTHORS:20110316-161027905
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Official Citation:Non-detection of L-band Line Emission from the Exoplanet HD189733b Avi M. Mandell et al. 2011 ApJ 728 18
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:22946
Deposited By: Jason Perez
Deposited On:29 Mar 2011 18:09
Last Modified:03 Oct 2019 02:41

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