Spitzer Space Telescope - General Observer Proposal #30070


Testing the first direct measurement of cataclysmic variable
evolution:  the search for a circumbinary disk or a low-mass companion
around NN Serpentis

Principal Investigator: Carolyn Brinkworth
           Institution: Caltech/JPL

Co-Investigators: 
Donald Hoard, Spitzer Science Center                                  
Tom Marsh, University of Warwick, UK                                  
Stefanie Wachter, Spitzer Science Center                              

Science Category: circumstellar/debris disks 
 Observing Modes: IracMap 
  Hours Approved: 1.6 

Abstract:
We obtained high time-resolution photometry using the high speed CCD
camera ULTRACAM between 2002 and 2004, which revealed a gradual
reduction in the orbital period of the pre-cataclysmic variable NN
Serpentis.  There are three possible explanations for this period
change:  firstly, we may have been successful in obtaining the first
and only direct measurement of the braking rate of a close binary
system, in which case our measured values are approximately 2 orders
of magnitude greater than predicted, and pose serious problems for the
theory of close binary evolution.  Secondly, the unusually high
braking rate may be caused by the presence of a circumbinary disk,
which would help to answer two of the outstanding problems with
current CV theory - namely the high mass-transfer rates seen in some
CVs, and the fact that the minimum observed value in the CV period
distribution is approximately 15% longer than expected.  Finally, our
observations could be explained by a light travel-time effect caused
by a third body in orbit around the binary, which would raise major
questions about the evolutionary history of the system, in particular
how a third body has managed to remain in a stable orbit throughout
periods of intense mass-loss in the central binary.  We intend to use
IRAC observations to search for a mid-infrared excess in the spectral
energy distribution of NN Ser, which would confirm the presence of
either a disk or a third body.  We then propose to use HST imaging to
attempt to resolve a third body, allowing us to discriminate between
the two possibilities.  If both methods fail to reveal any extra
system components, we will have ruled out our only remaining
alternatives to a genuinely high angular momentum loss rate in this
system, with profound implications for CV evolution.