Cool Stars 14 - Submitted Abstract # 108
This version created on 05 October 2006

The Dust and Gas Around beta Pictoris


Christine Chen, NOAO
Aigen Li, University of Missouri
Chris Bohac, University of Rochester
Kyoung Hee Kim, University of Rochester
Dan Watson, University of Rochester
Jeff van Cleve, Ball Aerospace
Jim Houck, Cornell
Karl Stapelfeldt, JPL
Michael Werner, JPL
George Rieke, University of Arizona
Kate Su, University of Arizona
Dana Backman, SOFIA/SETI Institute
Chas Beichman, Michelson Science Center
Giovanni Fazio, Harvard-Smithsonian Center for Astrophysics
Lee Hartmann, University of Michigan
Tom Megeath, University of Toledo

We have obtained Spitzer IRS 5.5 - 35 micron spectroscopy of the
debris disk around beta Pictoris.  In addition to the 10  micron
silicate emission feature originally observed from the ground, we for
the first time also detect the silicate emission bands at longer
wavelengths.  The IRS dust emission spectrum is well reproduced by a
dust model consisting of fluffy cometary and crystalline olivine
aggregates, with an additional population of warm dust to account for
the emission at lambda < 15 micron.  We searched for line emission
from molecular hydrogen and atomic S I, Fe II, and Si II gas but
detected none.  We place a 3 sigma upper limit of < 17 earth masses on
the molecular hydrogen S(1) gas mass, assuming an excitation
temperature of Tex= 100  K, suggesting that there is less gas in this
system than is required to form the envelope of Jupiter.  We
hypothesize that the atomic Na I gas observed in Keplerian rotation
around beta Pictoris may be produced by photon-stimulated desorption
from circumstellar dust grains.

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