Spitzer Space Telescope - General Observer Proposal #40466


Spectroscopy of the Exoplanet HD 209458b

Principal Investigator: Drake Deming
           Institution: NASA's Goddard Space Flight Center

     Technical Contact: Drake Deming, NASA's Goddard Space Flight Center

Co-Investigators: 
Sara Seager, MIT                                                      
Joseph Harrington, Univ. Central Florida                              
Carey Lisse, Johns Hopkins Applied Physics Laboratory                 
Jeremy Richardson, American Astronomical Society                      

Science Category: extrasolar planets 
 Observing Modes: IrsStare 
  Hours Approved: 28.4 

Abstract:
The spectra of two extrasolar planets (HD 209458b, and HD 189733b) have recently
been measured using Spitzer/IRS at 7 -14 microns. Both planets show a lack of
the water absorption that is expected to shape the IR spectra of these hot
Jupiters. We propose follow-up observations of HD 209458b at 5 - 8 microns (SL2
mode) to measure the large gradient in planetary flux that we know (from IRAC)
occurs over this wavelength range. Our observations will discriminate between
models wherein water is depleted chemically, versus masked by cloud opacity, and
will also provide information on the temperature gradient in the planet's
atmosphere. We also propose to repeat our 7 -14 micron spectroscopy of HD
209458b, where we detected an emission peak in the planet's spectrum at 9.7
microns. We identified this peak as due to silicate clouds. Our repeat
observations will use an improved technique, as recently developed by Grillmair
et al. for HD 189733b, which will allow us to better determine the details of
the silicate cloud composition.