Spitzer Space Telescope - Guaranteed Time Observer Proposal #30319


Exploring the Time Domain:  IRAC Photometric Monitoring of the Serpens
Cloud Core

Principal Investigator: Giovanni Fazio
           Institution: Harvard-Smithsonian Astrophysical Observatory

Co-Investigators: 
John Stauffer, SSC/JPL                                                
Luisa Rebull, SSC                                                     
S. Tom Megeath, CfA                                                   
Lori Allen, CfA                                                       
David Barrado y Navascues, LAEFF, Spain                               

Science Category: young stellar objects 
 Observing Modes: IracMap 
  Hours Approved: 15.4 

Abstract:
In the past year, several programs have demonstrated that IRACcan
provide extremely accurate and stable time-series photometry.  This
scientific capability has so far been used to detect the thermal
emission of extra-solar planets and to attempt to detect cloud
formations in the photospheres of brown dwarfs (brown dwarf
"weather").  We believe there is another topic where IRAC's very
stable photometry can break new ground.  We propose to use IRAC to
monitor a set of 50-100  very young PMS stars in the embedded
star-forming region of the Serpens cloud core.  Most of the stars in
this region are too embedded to monitor at optical wavelengths.
Monitoring could be done from the ground in the near-IR, but we
believe the much better stability (both photometric and PSF
width/shape) provided by IRAC will allow fundamentally different
science to be considered with our Spitzer data.  The variability of
PMS stars has been the subject of considerable effort in the optical
and in the near-IR, but this will be the first significant attempt
with IRAC and by far the most sensitive PMS star monitoring program
ever attempted in the mid-IR.  Based on previous optical and near-IR
efforts, we expect to see variability due to rotational modulation and
flaring.  We hope in addition we will be able to measure or place
limits on the time variability of the accretion onto the star as
reflected by the contribution to the system light of the inner disk
wall.  We regard this as an exploratory program - if we detect
variability in a significant fraction of the Serpens members and if we
can tie that variability to specific mechanisms that provide new
insight into how stars are assembled, then we expect our observations
will encourage others to propose similar programs for other regions.