Spitzer Space Telescope - General Observer Proposal #50747


As the World Turns: Discrete Observations of a Pseudo-Synchronized Eccentric
Transiting Planet

Principal Investigator: Bryce Croll
           Institution: University of Toronto

     Technical Contact: Bryce Croll, University of Toronto

Co-Investigators: 
David Lafreniere, University of Toronto                               
Ray Jayawardhana, University of Toronto                               
Jonathan Langton, University of California at Santa Cruz              
Gregory Laughlin, UCO/Lick Observatory                                
Norman Murray, Canadian Institute of Theoretical Astrophysics         

Science Category: extrasolar planets 
 Observing Modes: IracMap 
  Hours Approved: 30 

Abstract:
We propose to obtain precise IRAC 8-micron observations of the eccentric
transiting exoplanet HD 17156 b over three planetary spin periods. This newly
discovered transiting system is notable because (a) it experiences a 26-fold
increase in stellar insolation over its swing-in from apastron to periastron,
and (b) it is expected that tidal evolution has brought it in
pseudo-synchronization, with a resulting spin period of ~3.8d. This means that a
single face of the planet will be flash heated near periastron by an intense
blast of stellar irradiation that exceeds a 1000 times the solar flux at Earth.
The timescales for radiative cooling and advective transport of energy to the
other hemisphere after periastron passage have not yet been measured
observationally, and are a source of significant uncertainty in theoretical
models. Our proposed 8-micron observations will finely sample temperature
variations over one spin period of the planet near periastron, and coarsely
sample them over the preceding and following spin periods. To achieve the best
possible photometric precision, and approach the photon noise limit, we will
simultaneously observe (in full-array mode) a nearby reference star of similar
magnitude, thus minimizing systematic effects. Our observations are timely as
they require the unique high-precision mid-infrared capabilities of a cryogenic
Spitzer. These observations will allow us to determine the radiative and
advective timescales of this massive, gaseous exoplanet. An observational
constraint on these timescales for this planet will considerably advance our
understanding of the atmospheres of both eccentric gaseous and conventional hot
Jupiters.