Spitzer Space Telescope - Guaranteed Time Observer Proposal #50027


IRAC Imaging of Star-Cloud Collisions in the Pleiades

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

     Technical Contact: John Stauffer, Spitzer Science Center

Co-Investigators: 
Luisa M. Rebull, SSC                                                  
Patrick Lowrance, SSC                                                 
Inseok Song, SSC                                                      

Science Category: ISM 
 Observing Modes: IracMap 
  Hours Approved: 1.2 

Abstract:
The blue Palomar sky survey plate of the Pleiades region provides clear evidence
that there is considerable dust close to the bright stars of the Pleiades.
However, the network of dust filaments does not provide any unambiguous signpost
for the kinematics of the dust (and gas). Radial velocity measures of
interstellar absorption lines towards the bright Pleiades stars indicates that
the gas is moving towards the Pleiades at a relative velocity of about 10 km/s,
indicating that the gas/dust are not resident in the Pleiades but are instead
transiting through the cluster. White & Bally (1993) concluded that the Pleiades
was impacting the cloud from the East - and leaving a wake behind, visible in
the IRAS 60 and 100 micron images of the region. Herbig & Simon (2001) imaged
the brightest portion of the Merope nebula with HST, and concluded that the
shape of the nebula could only be explained by the gas impacting the Pleiades
from the south-southeast. Their conclusion was that the transiting cloud was an
outlyer from the Taurus molecular cloud. The two explanations are not
consistent. As part of a GTO program, we have obtained shallow IRAC imaging of
the center of the Pleiades and have identified two stars which appear to be
impacting cloud condensations at the current epoch, with extended circumstellar
dust prominent at 8 um. An additional star with similar characteristics has been
identified from FEPS data. A or F stars impacting moderate-density clouds should
carve paraboloidal cavities in the cloud (Artymowicz and Clampin 1997), with the
detailed shape of the cavity rim indicating the direction of relative motion of
the star and gas. We propose deep IRAC imaging of the three stars impacting the
passing cloud in order to define better the shape of their extended emission,
and hence determine the motion of the gas and dust relative to the Pleiades
stars.