Spitzer Space Telescope - General Observer Proposal #40325


Time-resolved observations of a roasted brown dwarf

Principal Investigator: Matt Burleigh
           Institution: University of Leicester

     Technical Contact: Matt Burleigh, University of Leicester

Co-Investigators: 
Pierre Maxted, University of Keele                                    
Ralf Napiwotzki, University of Hertfordshire                          
Paul Dobbie, Anglo-Australian Observatory                             
Carolyn Brinkworth, Spitzer Science Center                            
Donald Hoard, Spitzer Science Center                                  
Stefanie Wachter, Spitzer Science Center                              
Adam Burrows, University of Arizona                                   
Emma Hogan, University of Leicester                                   

Science Category: brown dwarfs/very low mass stars 
 Observing Modes: IracMap 
  Hours Approved: 4.2 

Abstract:
Irradiation of substellar brown dwarfs and hot Jupiters in close binaries can
increase their surface temperatures by an order of magnitude, alter their radii
and atmospheric structure, and lead to moderate mass loss. In these
synchronously rotating systems, substantial temperature diffences between the
"day" and "night" sides could lead to strong winds and jet streams transporting
heat to the "night" side. Variations between the brightness of the "day" and
"night " sides of the hot Jupiter upsilon And b have recently been detected by
Spitzer, but the contrast between star and planet prevents a more detailed
investigation. WD0137-349 is a unique close, detached binary containing a white
dwarf and a substellar secondary. The brown dwarf is clearly detected at near-IR
and mid-IR wavelengths. The hemisphere of the 0.053Msun brown dwarf facing the
16,500K white dwarf intercepts ~1% of its light and is being heated through
irradiation. K-band photometry reveals +/- 15% variations between the "day" and
"night" hemispheres. A short IRAC observation in Cycle 3 also reveals
significant variability over a period of just ten minutes. These data strongly
suggest that there are significant differences in luminosity and temperature
between the "day" and "night" hemispheres. We will obtain time-resolved IRAC
photometry of WD0137-349 in all four channels over the entire 116 minute orbital
period to make a detailed investigation of the heating effects on the brown
dwarf's atmosphere, and to accurately measure the temperature across the entire
surface. These observations will help us to understand how irradiation affects
the atmospheric structure and evolution of very cool, low mass objects, and to
develop and test new atmospheric models for irradiated brown dwarfs and hot
Jupiters.