TY - JOUR
T1 - Warm ice giant GJ 3470b I. A flat transmission spectrum indicates a hazy, low-methane, and/or metal-rich atmosphere?
AU - Crossfield, Ian J.M.
AU - Barman, Travis
AU - Hansen, Brad M.S.
AU - Howard, Andrew W.
N1 - Funding Information:
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.
PY - 2013
Y1 - 2013
N2 - 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 m 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 (5.4 confidence) or a moderate level of metal enrichment (50 solar abundances, 3.8), 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.
AB - 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 m 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 (5.4 confidence) or a moderate level of metal enrichment (50 solar abundances, 3.8), 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.
KW - Eclipses
KW - Planets and satellites: atmospheres
KW - Stars: individual: GJ 3470
KW - Techniques: photometric
KW - Techniques: spectroscopic
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U2 - 10.1051/0004-6361/201322278
DO - 10.1051/0004-6361/201322278
M3 - Article
AN - SCOPUS:84887040665
VL - 559
JO - Astronomy and Astrophysics
JF - Astronomy and Astrophysics
SN - 0004-6361
M1 - A33
ER -