TRANSMISSION SPECTRA OF TRANSITING PLANET ATMOSPHERES: MODEL VALIDATION AND SIMULATIONS OF THE HOT NEPTUNE GJ 436b FOR THE JAMES WEBB SPACE TELESCOPE

We explore the transmission spectrum of the Neptune-class exoplanet GJ 436b, including the possibility that its atmospheric opacity is dominated by a variety of nonequilibrium chemical products. We also validate our transmission code by demonstrating close agreement with analytic models that use only Rayleigh scattering or water vapor opacity. We find broad disagreement with radius variations predicted by another published model. For GJ 436b, the relative coolness of the planet's atmosphere, along with its implied high metallicity, may make it dissimilar in character compared to 'hot Jupiters'. Some recent observational and modeling efforts suggest low relative abundances of H{sub 2}O and CH{sub 4} present in GJ 436b's atmosphere, compared to calculations from equilibrium chemistry. We include these characteristics in our models and examine the effects of absorption from methane-derived higher-order hydrocarbons. To our knowledge, the effects of these nonequilibrium chemical products on the spectra of close-in giant planets have not previously been investigated. Significant absorption from HCN and C{sub 2}H{sub 2} is found throughout the infrared, while C{sub 2}H{sub 4} and C{sub 2}H{sub 6} are less easily seen. We perform detailed simulations of James Webb Space Telescope observations, including all likely noise sources, and find that we will be ablemore » to constrain chemical abundance regimes from this planet's transmission spectrum. For instance, the width of the features at 1.5, 3.3, and 7 {mu}m indicates the amount of HCN versus C{sub 2}H{sub 2} present. The NIRSpec prism mode will be useful due to its large spectral range and the relatively large number of photo-electrons recorded per spectral resolution element. However, extremely bright host stars like GJ 436 may be better observed with a higher spectroscopic resolution mode in order to avoid detector saturation. We find that observations with the MIRI low-resolution spectrograph should also have high signal-to-noise in the 5-10 {mu}m range due to the brightness of the star and the relatively low spectral resolution (R {approx} 100) of this mode.« less

[1]  W. Vacca,et al.  Accepted for publication in ApJ Preprint typeset using L ATEX style emulateapj v. 10/09/06 ATMOSPHERIC PARAMETERS OF FIELD L AND T DWARFS 1 , 2022 .

[2]  M. Holman,et al.  A SEARCH FOR ADDITIONAL PLANETS IN THE NASA EPOXI OBSERVATIONS OF THE EXOPLANET SYSTEM GJ 436 , 2009, 0909.2875.

[3]  Peter H. Hauschildt,et al.  Irradiated planets , 2001, astro-ph/0104262.

[4]  Drake Deming,et al.  Possible thermochemical disequilibrium in the atmosphere of the exoplanet GJ 436b , 2010, Nature.

[5]  J. Beaulieu,et al.  METHANE IN THE ATMOSPHERE OF THE TRANSITING HOT NEPTUNE GJ436B? , 2010, 1007.0324.

[6]  B. Fegley,et al.  Atmospheric Chemistry in Giant Planets, Brown Dwarfs, and Low-Mass Dwarf Stars. II. Sulfur and Phosphorus , 2005, astro-ph/0511136.

[7]  Debra A. Fischer,et al.  A Neptune-Mass Planet Orbiting the Nearby M Dwarf GJ 436 , 2004 .

[8]  Gautam Vasisht,et al.  The presence of methane in the atmosphere of an extrasolar planet , 2008, Nature.

[9]  A. D. Etangs,et al.  Rayleigh scattering in the transit spectrum of HD 189733b , 2008, 0802.3228.

[10]  G. Hebrard,et al.  Transit spectrophotometry of the exoplanet HD189733b. I. Searching for water but finding haze with HST NICMOS , 2009, 0907.4991.

[11]  Drake Deming,et al.  A SPITZER TRANSMISSION SPECTRUM FOR THE EXOPLANET GJ 436b, EVIDENCE FOR STELLAR VARIABILITY, AND CONSTRAINTS ON DAYSIDE FLUX VARIATIONS , 2011, 1104.2901.

[12]  C. Moutou,et al.  Detection of atmospheric haze on an extrasolar planet: the 0.55–1.05 μm transmission spectrum of HD 189733b with the Hubble Space Telescope , 2007, 0712.1374.

[13]  R. Redmer,et al.  Interior structure models of GJ 436b , 2010, 1002.4447.

[14]  A. Burrows,et al.  MODELS OF NEPTUNE-MASS EXOPLANETS: EMERGENT FLUXES AND ALBEDOS , 2009, 0909.2043.

[15]  M. Holman,et al.  Transit infrared spectroscopy of the hot Neptune around GJ 436 with the Hubble Space Telescope , 2008, 0810.5731.

[16]  D. Charbonneau,et al.  THE CLIMATE OF HD 189733b FROM FOURTEEN TRANSITS AND ECLIPSES MEASURED BY SPITZER , 2010, 1007.4378.

[17]  J. Tennyson,et al.  A H13CN/HN13C linelist, model atmospheres and synthetic spectra for carbon stars , 2008, 0807.0717.

[18]  Joseph L. Hora,et al.  THERMAL EMISSION AND TIDAL HEATING OF THE HEAVY AND ECCENTRIC PLANET XO-3b , 2010, 1001.2319.

[19]  S. Seager,et al.  Ocean Planet or Thick Atmosphere: On the Mass-Radius Relationship for Solid Exoplanets with Massive Atmospheres , 2007, 0710.4941.

[20]  M. Marley,et al.  ATMOSPHERIC CIRCULATION OF ECCENTRIC HOT NEPTUNE GJ436b , 2010, 1007.2942.

[21]  M. Holman,et al.  Accepted for publication in The Astrophysical Journal Preprint typeset using L ATEX style emulateapj v. 10/09/06 IMPROVED PARAMETERS FOR EXTRASOLAR TRANSITING PLANETS , 2008 .

[22]  I. Ribas,et al.  Primary and secondary eclipse spectroscopy with JWST exploring the exoplanet parameter space , 2010, 1008.0028.

[23]  R. Barnes.  Formation and evolution of exoplanets , 2010 .

[24]  J. Tennyson,et al.  A high-accuracy computed water line list , 2006, astro-ph/0601236.

[25]  J. Davy Kirkpatrick,et al.  New spectral types L and T , 2005 .

[26]  I. Ribas,et al.  Primary Transit of the Planet HD 189733b at 3.6 and 5.8 μm , 2007, 0711.2142.

[27]  A. P. Showman,et al.  TRANSMISSION SPECTRA OF THREE-DIMENSIONAL HOT JUPITER MODEL ATMOSPHERES , 2009, 0912.2350.

[28]  D. Ehrenreich,et al.  SEARCH FOR CARBON MONOXIDE IN THE ATMOSPHERE OF THE TRANSITING EXOPLANET HD 189733b , 2009, 0903.3405.

[29]  Mark Clampin,et al.  Discovery and Characterization of Transiting SuperEarths Using an All-Sky Transit Survey and Follow-Up by the James Webb Space Telescope , 2010 .

[30]  David A. Golimowski,et al.  THE 0.8–14.5 μm SPECTRA OF MID-L TO MID-T DWARFS: DIAGNOSTICS OF EFFECTIVE TEMPERATURE, GRAIN SEDIMENTATION, GAS TRANSPORT, AND SURFACE GRAVITY , 2009, 0906.2991.

[31]  Jonathan J. Fortney,et al.  The effect of condensates on the characterization of transiting planet atmospheres with transmission spectroscopy , 2005, astro-ph/0509292.

[32]  T. Brown,et al.  Detection of Planetary Transits Across a Sun-like Star , 1999, The Astrophysical journal.

[33]  Mark S. Marley,et al.  Synthetic Spectra and Colors of Young Giant Planet Atmospheres: Effects of Initial Conditions and Atmospheric Metallicity , 2008, 0805.1066.

[34]  Adam Burrows,et al.  PHOTOMETRIC AND SPECTRAL SIGNATURES OF THREE-DIMENSIONAL MODELS OF TRANSITING GIANT EXOPLANETS , 2010, 1005.0346.

[35]  Richard S. Freedman,et al.  A Unified Theory for the Atmospheres of the Hot and Very Hot Jupiters: Two Classes of Irradiated Atmospheres , 2007, 0710.2558.

[36]  Portugal,et al.  Accurate Spitzer infrared radius measurement for the hot Neptune GJ 436b , 2007, 0707.2261.

[37]  J. Lunine,et al.  Reflected Spectra and Albedos of Extrasolar Giant Planets. I. Clear and Cloudy Atmospheres , 1998, astro-ph/9810073.

[38]  D. Queloz,et al.  Detection of transits of the nearby hot Neptune GJ 436 b , 2007, Astronomy & Astrophysics.

[39]  R. Gilliland,et al.  Detection of an Extrasolar Planet Atmosphere , 2001, astro-ph/0111544.

[40]  T. Guillot,et al.  A Nongray Theory of Extrasolar Giant Planets and Brown Dwarfs , 1997, astro-ph/9705201.

[41]  I. Ribas,et al.  Water in HD 209458b's atmosphere from 3.6 - 8 microns IRAC photometric observations in primary transit , 2009, 0909.0185.

[42]  G. Laughlin,et al.  Discovery and Characterization of Transiting Super Earths Using an All-Sky Transit Survey and Follow-up by the James Webb Space Telescope , 2009, 0903.4880.

[43]  A. Burrows,et al.  Theory of Extrasolar Giant Planet Transits , 2001, astro-ph/0101024.

[44]  T. Barman.  Identification of Absorption Features in an Extrasolar Planet Atmosphere , 2007, 0704.1114.

[45]  S. Seager,et al.  HIGH METALLICITY AND NON-EQUILIBRIUM CHEMISTRY IN THE DAYSIDE ATMOSPHERE OF HOT-NEPTUNE GJ 436b , 2010, 1004.5121.

[46]  R. P. Butler,et al.  The M Dwarf GJ 436 and its Neptune‐Mass Planet , 2006, astro-ph/0608260.

[47]  P. McCullough,et al.  PROBING THE TERMINATOR REGION ATMOSPHERE OF THE HOT-JUPITER XO-1b WITH TRANSMISSION SPECTROSCOPY , 2010, 1002.2434.

[48]  E. Observatory,et al.  High cadence near infrared timing observations of extrasolar planets , 2009, 0905.1728.

[49]  Jonathan Tennyson,et al.  Water vapour in the atmosphere of a transiting extrasolar planet , 2007, Nature.

[50]  Carl J. Grillmair,et al.  Strong water absorption in the dayside emission spectrum of the planet HD 189733b , 2008, Nature.

[51]  M. Marley,et al.  Line and Mean Opacities for Ultracool Dwarfs and Extrasolar Planets , 2007, 0706.2374.

[52]  A. Burrows,et al.  On the Indirect Detection of Sodium in the Atmosphere of the Planetary Companion to HD 209458 , 2002, astro-ph/0208263.

[53]  M. Marley,et al.  Thermometric Soots on Warm Jupiters , 2009, 0911.0728.

[54]  AZ,et al.  Characterization of the hot Neptune GJ 436 b with Spitzer and ground-based observations , 2007, 0707.3809.

[55]  D. Sasselov,et al.  THE ATMOSPHERIC SIGNATURES OF SUPER-EARTHS: HOW TO DISTINGUISH BETWEEN HYDROGEN-RICH AND HYDROGEN-POOR ATMOSPHERES , 2008, 0808.1902.

[56]  T. Brown.  Transmission Spectra as Diagnostics of Extrasolar Giant Planet Atmospheres , 2001, astro-ph/0101307.

[57]  Drake Deming,et al.  Spitzer Transit and Secondary Eclipse Photometry of GJ 436b , 2007, 0707.2778.

[58]  K. Lodders,et al.  ATMOSPHERIC SULFUR PHOTOCHEMISTRY ON HOT JUPITERS , 2009, 0903.1663.

[59]  M. Osorio,et al.  Earth’s transmission spectrum from lunar eclipse observations , 2009, Nature.

[60]  S. Seager,et al.  A TEMPERATURE AND ABUNDANCE RETRIEVAL METHOD FOR EXOPLANET ATMOSPHERES , 2009, 0910.1347.

[61]  Princeton,et al.  Theoretical Transmission Spectra during Extrasolar Giant Planet Transits , 1999, astro-ph/9912241.

[62]  Markus Loose,et al.  Detector arrays for the James Webb Space Telescope near-infrared spectrograph , 2004, SPIE Optical Engineering + Applications.

[63]  R. P. Butler,et al.  A Transiting “51 Peg-like” Planet , 2000, The Astrophysical journal.

[64]  A. Burrows,et al.  Atomic and Molecular Opacities for Brown Dwarf and Giant Planet Atmospheres , 2006, astro-ph/0607211.

[65]  E. Lellouch,et al.  Photochemistry and diffusion in Jupiter's stratosphere: Constraints from ISO observations and comparisons with other giant planets , 2005 .

[66]  Ammonia as a tracer of chemical equilibrium in the T7.5 dwarf Gliese 570D , 2006, astro-ph/0605563.

[67]  Sara Seager,et al.  On the Insignificance of Photochemical Hydrocarbon Aerosols in the Atmospheres of Close-in Extrasolar Giant Planets , 2004 .

[68]  B. Fegley,et al.  Atmospheric Chemistry in Giant Planets, Brown Dwarfs, and Low-Mass Dwarf Stars: I. Carbon, Nitrogen, and Oxygen , 2002 .

[69]  Comparative Planetary Atmospheres: Models of TrES-1 and HD 209458b , 2005, astro-ph/0505359.

[70]  France.,et al.  Limits to the planet candidate GJ 436c , 2008, 0804.3030.

[71]  Harry Partridge,et al.  The determination of an accurate isotope dependent potential energy surface for water from extensive ab initio calculations and experimental data , 1997 .

[72]  Adam Burrows,et al.  ALBEDO AND REFLECTION SPECTRA OF EXTRASOLAR GIANT PLANETS , 1999 .