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Infrared Transmission Spectroscopy of the Exoplanets HD209458b and XO-1b Using the Wide Field Camera-3 on the Hubble Space Telescope

Deming, Drake and Wilkins, Ashlee and McCullough, Peter and Burrows, Adam and Fortney, Jonathan J. and Agol, Eric and Dobbs-Dixon, Ian and Madhusudhan, Nikku and Crouzet, Nicolas and Désert, Jean-Michel and Gilliland, Ronald L. and Haynes, Korey and Knutson, Heather A. and Line, Michael and Magic, Zazralt and Mandell, Avi M. and Ranjan, Sukrit and Charbonneau, David and Clampin, Mark and Seager, Sara and Showman, Adam P. (2013) Infrared Transmission Spectroscopy of the Exoplanets HD209458b and XO-1b Using the Wide Field Camera-3 on the Hubble Space Telescope. Astrophysical Journal, 774 (2). Art. No. 95. ISSN 0004-637X. doi:10.1088/0004-637X/774/2/95.

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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.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Deming, Drake0000-0001-5727-4094
McCullough, Peter0000-0001-9165-9799
Burrows, Adam0000-0002-3099-5024
Fortney, Jonathan J.0000-0002-9843-4354
Agol, Eric0000-0002-0802-9145
Dobbs-Dixon, Ian0000-0002-4989-6501
Madhusudhan, Nikku0000-0002-4869-000X
Désert, Jean-Michel0000-0002-0875-8401
Gilliland, Ronald L.0000-0002-1554-5578
Knutson, Heather A.0000-0002-0822-3095
Line, Michael0000-0002-2338-476X
Mandell, Avi M.0000-0002-8119-3355
Charbonneau, David0000-0002-9003-484X
Seager, Sara0000-0002-6892-6948
Additional Information:© 2013 American Astronomical Society. Received 2013 February 5, accepted for publication 2013 July 10; Published 2013 August 20. We are grateful for the excellent support of the staff at STScI for the scheduling and execution of our demanding observations, especially our contact person Shelly Meyett. We also thank an anonymous referee for insightful comments that improved this paper.
Subject Keywords:planetary systems; planets and satellites: atmospheres; techniques: photometric; techniques: spectroscopic
Issue or Number:2
Record Number:CaltechAUTHORS:20130722-101038892
Persistent URL:
Official Citation:Infrared Transmission Spectroscopy of the Exoplanets HD 209458b and XO-1b Using the Wide Field Camera-3 on the Hubble Space Telescope Drake Deming et al. 2013 ApJ 774 95
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:39492
Deposited By: Tony Diaz
Deposited On:12 Aug 2013 21:11
Last Modified:09 Nov 2021 23:45

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