INFRARED TRANSMISSION SPECTROSCOPY OF THE EXOPLANETS HD 209458b AND XO-1b USING THE WIDE FIELD CAMERA-3 ON THE HUBBLE SPACE TELESCOPE

Exoplanetary transmission spectroscopy in the near-infrared using the Hubble Space Telescope (HST) NICMOS is currently ambiguous because different observational groups claim different results from the same data, depending on their analysis methodologies. Spatial scanning with HST/WFC3 provides an opportunity to resolve this ambiguity. We here report WFC3 spectroscopy of the giant planets HD 209458b and XO-1b in transit, using spatial scanning mode for maximum photon-collecting efficiency. We introduce an analysis technique that derives the exoplanetary transmission spectrum without the necessity of explicitly decorrelating instrumental effects, and achieves nearly photon-limited precision even at the high flux levels collected in spatial scan mode. Our errors are within 6% (XO-1) and 26% (HD 209458b) of the photon-limit at a resolving power of λ/δλ ~ 70, and are better than 0.01% per spectral channel. Both planets exhibit water absorption of approximately 200 ppm at the water peak near 1.38 μm. Our result for XO-1b contradicts the much larger absorption derived from NICMOS spectroscopy. The weak water absorption we measure for HD 209458b is reminiscent of the weakness of sodium absorption in the first transmission spectroscopy of an exoplanet atmosphere by Charbonneau et al. Model atmospheres having uniformly distributed extra opacity of 0.012 cm2 g−1 account approximately for both our water measurement and the sodium absorption. Our results for HD 209458b support the picture advocated by Pont et al. in which weak molecular absorptions are superposed on a transmission spectrum that is dominated by continuous opacity due to haze and/or dust. However, the extra opacity needed for HD 209458b is grayer than for HD 189733b, with a weaker Rayleigh component.

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

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

[3]  D. Ehrenreich,et al.  GTC OSIRIS transiting exoplanet atmospheric survey: detection of sodium in XO-2b from differential long-slit spectroscopy† , 2012, 1208.4982.

[4]  Sara Seager,et al.  THE OPTICAL AND NEAR-INFRARED TRANSMISSION SPECTRUM OF THE SUPER-EARTH GJ 1214b: FURTHER EVIDENCE FOR A METAL-RICH ATMOSPHERE , 2011, 1109.0582.

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

[6]  D. Ehrenreich,et al.  Gran Telescopio Canarias OSIRIS transiting exoplanet atmospheric survey: detection of potassium in XO-2b from narrowband spectrophotometry , 2010, 1008.4795.

[7]  Joseph L. Hora,et al.  Accepted for publication in The Astrophysical Journal Preprint typeset using L ATEX style emulateapj v. 10/09/06 THERMAL EMISSION OF EXOPLANET XO-1B , 2022 .

[8]  P. Bernath,et al.  Laboratory Spectroscopy of Hot Water near 2 Microns and Sunspot Spectroscopy in the H-Band Region , 2002 .

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

[10]  A. Burrows,et al.  THEORETICAL TRANSIT SPECTRA FOR GJ 1214b AND OTHER “SUPER-EARTHS” , 2012, 1203.1921.

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

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

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

[14]  P. Gilman,et al.  Rotation of the sun measured from Mount Wilson white-light images , 1984 .

[15]  M. Asplund,et al.  Limb darkening laws for two exoplanet host stars derived from 3D stellar model atmospheres Comparison with 1D models and HST light curve observations , 2012, 1202.0548.

[16]  Thomas P. Greene,et al.  TRANSMISSION SPECTRA OF TRANSITING PLANET ATMOSPHERES: MODEL VALIDATION AND SIMULATIONS OF THE HOT NEPTUNE GJ 436b FOR THE JAMES WEBB SPACE TELESCOPE , 2010, 1010.2451.

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

[18]  Nikole K. Lewis,et al.  DOPPLER SIGNATURES OF THE ATMOSPHERIC CIRCULATION ON HOT JUPITERS , 2011, 1207.5639.

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

[20]  D. Ehrenreich,et al.  Determining Atmospheric Conditions at the Terminator of the Hot Jupiter HD 209458b , 2008, 0803.1054.

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

[22]  L. Walkowicz,et al.  PHOTOMETRIC VARIABILITY IN KEPLER TARGET STARS: THE SUN AMONG STARS—A FIRST LOOK , 2010, 1001.0414.

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

[24]  Jacob L. Bean,et al.  A ground-based transmission spectrum of the super-Earth exoplanet GJ 1214b , 2010, Nature.

[25]  A. Borysow,et al.  Collision-induced absorption coefficients of H2 pairs at temperatures from 60 K to 1000 K , 2002 .

[26]  D. Ehrenreich,et al.  TiO and VO broad band absorption features in the optical spectrum of the atmosphere of the hot-Jupiter HD 209458b , 2008, 0809.1865.

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

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

[29]  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.

[30]  Simon Albrecht,et al.  The orbital motion, absolute mass and high-altitude winds of exoplanet HD 209458b , 2010, Nature.

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

[32]  M. Penn,et al.  Solar Cycle Changes in Sunspot Umbral Intensity , 2007 .

[33]  Nicolas Crouzet,et al.  TRANSMISSION SPECTROSCOPY OF EXOPLANET XO-2b OBSERVED WITH HUBBLE SPACE TELESCOPE NICMOS , 2012, 1210.5275.

[34]  Drake Deming,et al.  Spitzer/MIPS 24 μm OBSERVATIONS OF HD 209458b: THREE ECLIPSES, TWO AND A HALF TRANSITS, AND A PHASE CURVE CORRUPTED BY INSTRUMENTAL SENSITIVITY VARIATIONS , 2012, 1202.1562.

[35]  A. Borysow,et al.  Rototranslational Collision-induced Absorption by H 2--H 2 Pairs at Temperatures from 600 to 7000 K , 1995 .

[36]  E. Ford.  QUANTIFYING THE UNCERTAINTY IN THE ORBITS OF EXTRASOLAR PLANETS , 2003, astro-ph/0305441.

[37]  Jonathan Tennyson,et al.  BLIND EXTRACTION OF AN EXOPLANETARY SPECTRUM THROUGH INDEPENDENT COMPONENT ANALYSIS , 2013, 1301.4041.

[38]  S. Aigrain,et al.  A Gaussian process framework for modelling instrumental systematics: application to transmission spectroscopy , 2011, 1109.3251.

[39]  J. Fortney,et al.  THE FLAT TRANSMISSION SPECTRUM OF THE SUPER-EARTH GJ1214b FROM WIDE FIELD CAMERA 3 ON THE HUBBLE SPACE TELESCOPE , 2011, 1111.5621.

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

[41]  Peter H. Hauschildt,et al.  TiO and H2O Absorption Lines in Cool Stellar Atmospheres , 2000, astro-ph/0008465.

[42]  M. Marley,et al.  Atmospheric Circulation of Hot Jupiters: Three-dimensional Circulation Models of HD 209458b and HD 189733b with Simplified Forcing , 2008, 0802.0327.

[43]  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.

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

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

[46]  N. Crouzet,et al.  WATER VAPOR IN THE SPECTRUM OF THE EXTRASOLAR PLANET HD 189733b. I. THE TRANSIT , 2014, 1407.2462.

[47]  P. Bernath,et al.  Water on the sun. , 1995, Science.

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

[49]  E. Bergeron,et al.  NICMOS OBSERVATIONS OF THE TRANSITING HOT JUPITER XO-1b , 2010, 1006.1953.

[50]  University of Exeter,et al.  A new look at NICMOS transmission spectroscopy of HD 189733, GJ-436 and XO-1: no conclusive evidence for molecular features , 2010, 1010.1753.

[51]  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 .

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

[53]  Aisey M Andel.  ANALYTIC LIGHTCURVES FOR PLANETARY TRANSIT SEARCHES , 2002 .

[54]  S. Albrecht,et al.  Ground-based detection of sodium in the transmission spectrum of exoplanet HD209458b , 2008, 0805.0789.

[55]  S. Aigrain,et al.  The prevalence of dust on the exoplanet HD 189733b from Hubble and Spitzer observations , 2012, 1210.4163.

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

[57]  S. Seager,et al.  ON THE INFERENCE OF THERMAL INVERSIONS IN HOT JUPITER ATMOSPHERES , 2010, 1010.4585.

[58]  K. Menou,et al.  THREE-DIMENSIONAL ATMOSPHERIC CIRCULATION MODELS OF HD 189733b AND HD 209458b WITH CONSISTENT MAGNETIC DRAG AND OHMIC DISSIPATION , 2012, 1208.2274.

[59]  Ingo P. Waldmann,et al.  OF “COCKTAIL PARTIES” AND EXOPLANETS , 2011, 1106.1989.

[60]  E. Agol,et al.  THE IMPACT OF CIRCUMPLANTARY JETS ON TRANSIT SPECTRA AND TIMING OFFSETS FOR HOT JUPITERS , 2011, 1110.4377.

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

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

[63]  S. Bloemen,et al.  Gravity and limb-darkening coefficients for the Kepler, CoRoT, Spitzer, uvby, UBVRIJHK, and Sloan photometric systems , 2011 .

[64]  P. Greenfield,et al.  INSTRUMENT SCIENCE REPORT , 1995 .