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 S Barman, Brad M S Hansen, Andrew W. Howard

Research output: Contribution to journalArticle

25 Citations (Scopus)

Abstract

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.

Original languageEnglish (US)
Article numberA33
JournalAstronomy and Astrophysics
Volume559
DOIs
StatePublished - 2013
Externally publishedYes

Fingerprint

ice
methane
planet
atmospheres
atmosphere
metal
metals
extrasolar planets
wavelength
spectrographs
planets
haze
cirrus
disequilibrium
free atmosphere
bulk density
spectroscopy
high altitude
transit
wavelengths

Keywords

  • Eclipses
  • Planets and satellites: atmospheres
  • Stars: individual: GJ 3470
  • Techniques: photometric
  • Techniques: spectroscopic

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Warm ice giant GJ 3470b I. A flat transmission spectrum indicates a hazy, low-methane, and/or metal-rich atmosphere? / Crossfield, Ian J M; Barman, Travis S; Hansen, Brad M S; Howard, Andrew W.

In: Astronomy and Astrophysics, Vol. 559, A33, 2013.

Research output: Contribution to journalArticle

@article{f4e32dca54f241c6b89d2dc7050e13dd,
title = "Warm ice giant GJ 3470b I. A flat transmission spectrum indicates a hazy, low-methane, and/or metal-rich atmosphere?",
abstract = "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.",
keywords = "Eclipses, Planets and satellites: atmospheres, Stars: individual: GJ 3470, Techniques: photometric, Techniques: spectroscopic",
author = "Crossfield, {Ian J M} and Barman, {Travis S} and Hansen, {Brad M S} and Howard, {Andrew W.}",
year = "2013",
doi = "10.1051/0004-6361/201322278",
language = "English (US)",
volume = "559",
journal = "Astronomy and Astrophysics",
issn = "0004-6361",
publisher = "EDP Sciences",

}

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 S

AU - Hansen, Brad M S

AU - Howard, Andrew W.

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

UR - http://www.scopus.com/inward/record.url?scp=84887040665&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=84887040665&partnerID=8YFLogxK

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 -