The Broadband Infrared Emission Spectrum of the Exoplanet HD 189733b

We present Spitzer Space Telescope time series photometry of the exoplanet system HD 189733 spanning two times of secondary eclipse, when the planet passes out of view behind the parent star. We estimate the relative eclipse depth in five distinct bands and find the planet-to-star flux ratio to be 0.256% ± 0.014% (3.6 μm), 0.214% ± 0.020% (4.5 μm), 0.310% ± 0.034% (5.8 μm), 0.391% ± 0.022% (8.0 μm), and 0.598% ± 0.038% (24 μm). For consistency, we reanalyze a previously published time series to deduce a contrast ratio in an additional band, 0.519% ± 0.020% (16 μm). Our data are strongly inconsistent with a Planck spectrum, and we clearly detect emission near 4 μm as predicted by published theoretical models in which this feature arises from a corresponding opacity window. Unlike recent results for the exoplanet HD 209458b, we find that the emergent spectrum from HD 189733b is best matched by models that do not include an atmospheric temperature inversion. Taken together, these two studies provide initial observational support for the idea that hot Jupiter atmospheres diverge into two classes, in which a thermal inversion layer is present for the more strongly irradiated objects.

[1]  Drake Deming,et al.  Infrared radiation from an extrasolar planet , 2005, Nature.

[2]  David Charbonneau,et al.  Theoretical Spectral Models of the Planet HD 209458b with a Thermal Inversion and Water Emission Bands , 2007, 0709.3980.

[3]  D. James,et al.  A new upper limit on the reflected starlight from τ Bootis b , 2003, astro-ph/0308413.

[4]  Drake Deming,et al.  A New Search for Carbon Monoxide Absorption in the Transmission Spectrum of the Extrasolar Planet HD 209458b , 2004, astro-ph/0412436.

[5]  T. Barman.  On the Presence of Water and Global Circulation in the Transiting Planet HD 189733b , 2008, 0802.0854.

[6]  David Charbonneau,et al.  Using Stellar Limb-Darkening to Refine the Properties of HD 209458b , 2006, astro-ph/0603542.

[7]  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.

[8]  A. P. Showman,et al.  The Influence of Atmospheric Dynamics on the Infrared Spectra and Light Curves of Hot Jupiters , 2006 .

[9]  M. Mayor,et al.  An extended upper atmosphere around the extrasolar planet HD209458b , 2003, Nature.

[10]  David W. Latham,et al.  A STELLAR COMPANION IN THE HD 189733 SYSTEM WITH A KNOWN TRANSITING EXTRASOLAR PLANET , 2006 .

[11]  C. Moutou,et al.  Searching for helium in the exosphere of HD 209458b , 2003 .

[12]  A. Boss,et al.  Protostars and Planets VI , 2000 .

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

[14]  Avi Shporer,et al.  The Transit Light Curve Project. VII. The Not-So-Bloated Exoplanet HAT-P-1b , 2007, 0707.1908.

[15]  Paul S. Smith,et al.  The Multiband Imaging Photometer for Spitzer (MIPS) , 2004 .

[16]  Drake Deming,et al.  Scientific Frontiers in Research on Extrasolar Planets , 2003 .

[17]  S. Seager,et al.  Toward Eclipse Mapping of Hot Jupiters , 2006, astro-ph/0612412.

[18]  David Charbonneau,et al.  The 3.6-8.0 μm Broadband Emission Spectrum of HD 209458b: Evidence for an Atmospheric Temperature Inversion , 2007, 0709.3984.

[19]  K. Horne,et al.  A search for starlight reflected from ν And's innermost planet , 2001 .

[20]  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.

[21]  A. Burrows,et al.  A Spitzer Spectrum of the Exoplanet HD 189733b , 2007 .

[22]  Drake Deming,et al.  Accepted for publication in the Astrophysical Journal Strong Infrared Emission from the Extrasolar Planet HD189733b , 2006 .

[23]  I. Hubeny,et al.  Theory for the Secondary Eclipse Fluxes, Spectra, Atmospheres, and Light Curves of Transiting Extrasolar Giant Planets , 2006, astro-ph/0607014.

[24]  G. Fazio,et al.  The Infrared Array Camera (IRAC) for the Spitzer Space Telescope , 2004, astro-ph/0405616.

[25]  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 .

[26]  E. Agol,et al.  Analytic Light Curves for Planetary Transit Searches , 2002, astro-ph/0210099.

[27]  Drake Deming,et al.  A Ground‐based Search for Thermal Emission from the Exoplanet TrES‐1 , 2007, 0705.4288.

[28]  R. Akeson,et al.  The Mid-Infrared Spectrum of the Transiting Exoplanet HD 209458b , 2007, astro-ph/0702593.

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

[30]  David Charbonneau,et al.  TrES-3: A Nearby, Massive, Transiting Hot Jupiter in a 31 Hour Orbit , 2007, 0705.2004.

[31]  Athena Coustenis,et al.  Search for spectroscopical signatures of transiting HD 209458b's exosphere , 2001 .

[32]  Drake Deming,et al.  The Phase-Dependent Infrared Brightness of the Extrasolar Planet ʊ Andromedae b , 2006, Science.

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

[34]  David Charbonneau,et al.  Detection of Thermal Emission from an Extrasolar Planet , 2005 .

[35]  I. Hubeny,et al.  Possible Solutions to the Radius Anomalies of Transiting Giant Planets , 2006 .

[36]  Drake Deming,et al.  Infrared Observations During the Secondary Eclipse of HD 209458b: I. 3.6-Micron Occultation Spectroscopy Using the VLT , 2002 .

[37]  Drake Deming,et al.  3.8-μm photometry during the secondary eclipse of the extrasolar planet HD 209458b , 2007, 0704.1306.

[38]  David Charbonneau,et al.  A map of the day–night contrast of the extrasolar planet HD 189733b , 2007, Nature.

[39]  E. Covino,et al.  K‐band transit and secondary eclipse photometry of exoplanet OGLE‐TR‐113b , 2006 .

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

[41]  Sara Seager,et al.  Hot Jupiter Variability in Eclipse Depth , 2006, astro-ph/0612413.

[42]  E. Turner,et al.  A search for Hα absorption in the exosphere of the transiting extrasolar planet HD 209458b , 2004, astro-ph/0404469.

[43]  David Charbonneau,et al.  An Upper Limit on the Reflected Light from the Planet Orbiting the Star τ Bootis , 1999, astro-ph/9907195.

[44]  T. Barman,et al.  Limits on the 2.2-μm contrast ratio of the close-orbiting planet HD 189733b , 2007, 0708.4300.

[45]  Michel Mayor,et al.  ELODIE metallicity-biased search for transiting Hot Jupiters. II. A very hot Jupiter transiting the bright K star HD 189733 , 2005 .

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

[47]  K. Keil,et al.  Protostars and Planets V , 2007 .

[48]  J. Fortney,et al.  Resolving the Surfaces of Extrasolar Planets with Secondary Eclipse Light Curves , 2006, astro-ph/0601092.

[49]  S. T. Megeath,et al.  A Sensitive Search for Variability in Late L Dwarfs: The Quest for Weather , 2005 .

[50]  Mark S. Marley,et al.  Analysis of Spitzer Spectra of Irradiated Planets: Evidence for Water Vapor? , 2007, 0705.2457.

[51]  Tristan Guillot,et al.  Atmospheric circulation and tides of ``51 Pegasus b-like'' planets , 2002 .

[52]  I. Hubeny,et al.  A theoretical interpretation of the measurements of the secondary eclipses of tres-1 and HD 209458b , 2005 .

[53]  I. Snellen.  High-precision K-band photometry of the secondary eclipse of HD 209458 , 2005, astro-ph/0507618.

[54]  Avi Shporer,et al.  The Transit Light Curve Project. V. System Parameters and Stellar Rotation Period of HD 189733 , 2006, astro-ph/0612224.

[55]  Drake Deming,et al.  The hottest planet , 2007, Nature.

[56]  Martin G. Cohen,et al.  Absolute Calibration of the Infrared Array Camera on the Spitzer Space Telescope , 2005, astro-ph/0507139.

[57]  R. Kuschnig,et al.  An Upper Limit on the Albedo of HD 209458b: Direct Imaging Photometry with the MOST Satellite , 2006 .

[58]  Drake Deming,et al.  A spectrum of an extrasolar planet , 2007, Nature.

[59]  L. J. Richardson,et al.  On the Dayside Thermal Emission of Hot Jupiters , 2005 .

[60]  David Charbonneau,et al.  TrES-4: A Transiting Hot Jupiter of Very Low Density , 2007, 0708.0834.

[61]  Peter H. Hauschildt,et al.  Phase-dependent Properties of Extrasolar Planet Atmospheres , 2005 .

[62]  G. Laughlin,et al.  On the Radii of Extrasolar Giant Planets , 2003 .

[63]  Drake Deming,et al.  Infrared Observations during the Secondary Eclipse of HD 209458b. II. Strong Limits on the Infrared Spectrum Near 2.2 μm , 2003, astro-ph/0307297.

[64]  I. Hubeny,et al.  Theoretical Spectra and Light Curves of Close-in Extrasolar Giant Planets and Comparison with Data , 2007, 0709.4080.

[65]  Curtis S. Cooper,et al.  Dynamics and Disequilibrium Carbon Chemistry in Hot Jupiter Atmospheres, with Application to HD 209458b , 2006 .

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

[67]  J. Fortney,et al.  The Search for an Atmospheric Signature of the Transiting Exoplanet HD 149026b , 2006, astro-ph/0609513.

[68]  E. Wright,et al.  The Spitzer Space Telescope Mission , 2004, astro-ph/0406223.

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

[70]  I. Hubeny,et al.  A Possible Bifurcation in Atmospheres of Strongly Irradiated Stars and Planets , 2003 .

[71]  L. Koesterke,et al.  Sodium Absorption from the Exoplanetary Atmosphere of HD 189733b Detected in the Optical Transmission Spectrum , 2007, 0712.0761.

[72]  R. Gilliland,et al.  Exploring the Potential of Integral Field Spectroscopy for Observing Extrasolar Planet Transits: Ground‐based Observations of the Atmospheric Na in HD 209458b , 2005, astro-ph/0509407.