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Warm ice giant GJ 3470b. I. A flat transmission spectrum indicates a hazy, low-methane, and/or metal-rich atmosphere

Crossfield, Ian J. M. and Barman, Travis and Hansen, Brad M. S. and Howard, Andrew W. (2013) Warm ice giant GJ 3470b. I. A flat transmission spectrum indicates a hazy, low-methane, and/or metal-rich atmosphere. Astronomy and Astrophysics, 559 . Art. No. A33. ISSN 0004-6361.

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We report our spectroscopic investigation of the transiting ice giant GJ 3470b’s atmospheric transmission, and the first results of extrasolar planet observations from the new Keck/MOSFIRE spectrograph. We measure a planet/star radius ratio of 0.0789^(+0.0021)_(-0.0019) in a bandpass from 2.09–2.36 μm and in six narrower bands across this wavelength range. When combined with existing broadband photometry, these measurements rule out cloud-free atmospheres in chemical equilibrium assuming either solar abundances (5.4σ confidence) or a moderate level of metal enrichment (50× solar abundances, 3.8σ), confirming previous results that such models are not representative for cool, low-mass, externally irradiated extrasolar planets. Current measurements are consistent with a flat transmission spectrum, which suggests that the atmosphere is explained by high-altitude clouds and haze, disequilibrium chemistry, unexpected abundance patterns, or the atmosphere is extremely metal-rich (≳200 × solar). Because GJ 3470b’s low bulk density sets an upper limit on the planet’s atmospheric enrichment of ≲300 × solar, the atmospheric mean molecular weight must be ≲9. Thus, if the atmosphere is cloud-free its spectral features should be detectable with future observations. Transit observations at shorter wavelengths will provide the best opportunity to discriminate between plausible scenarios. We obtained optical spectroscopy with the GMOS spectrograph, but these observations exhibit large systematic uncertainties owing to thin, persistent cirrus conditions. Finally, we also provide the first detailed look at the steps necessary for well-calibrated MOSFIRE observations, and provide advice for future observations with this instrument.

Item Type:Article
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URLURL TypeDescription Paper
Crossfield, Ian J. M.0000-0002-1835-1891
Barman, Travis0000-0002-7129-3002
Hansen, Brad M. S.0000-0001-7840-3502
Howard, Andrew W.0000-0001-8638-0320
Additional Information:© 2013 ESO. Article published by EDP Sciences. Received 14 July 2013; Accepted 29 August 2013; Published online 31 October 2013. We thank P. Cubillos and Dr. J. Harrington for in-depth discussions about the finer points of light-curve fitting and systematic uncertainties, Dr. H. Knutson for discussions of GJ 436b and its transmission spectrum, Dr. M. Kassis, J. Aycock, Dr. P. Hirst, and B. Walp for their assistance in obtaining our MOSFIRE and GMOS observations, and Drs. I. McLean and K. Kulas for useful discussions regarding the MOSFIRE instrument. This material is based upon work supported by NASA Origins of Solar Systems under Grant No. NNX10AH31G awarded to T.B.
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Subject Keywords:techniques: spectroscopic – techniques: photometric – planets and satellites: atmospheres – stars: individual: GJ 3470 – eclipses
Record Number:CaltechAUTHORS:20170623-154020107
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Official Citation:Warm ice giant GJ 3470b - I. A flat transmission spectrum indicates a hazy, low-methane, and/or metal-rich atmosphere Ian J. M. Crossfield, Travis Barman, Brad M. S. Hansen and Andrew W. Howard A&A, 559 (2013) A33 DOI:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:78530
Deposited By: Tony Diaz
Deposited On:27 Jun 2017 20:49
Last Modified:14 Oct 2019 21:47

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