9930(  1) - 04/04/03 10:21  - [  1]

    PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS   ST ScI Use Only
                                                       ID:      9930
                                                       Version: 1
                                                       Check-in Date: 04-Apr-2003
                                                                      10:21:21

1.Proposal Title:
Models of Gas in Disks of Classical T Tauri Stars
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2. Proposal For  3. Cycle
AR               11
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4. Investigators
                                                                                     Contact?
    PI: Gregory Herczeg                   University of Colorado at Boulder
   CoI: Mr. Matthew Browning              University of Colorado at Boulder             N
   CoI: Dr. Jeffrey Linsky                University of Colorado at Boulder             N

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5. Abstract

The formation of planets and planetessimals is very sensitive to the presence and
structure of gas in the environment. While models of dust in disks of Classical T
Tauri Stars (CTTSs) have reproduced the observed IR-to-mm spectral energy
distibutions (SEDs) to determine dust masses, grain sizes, and disk lifetimes, until
now the gas in disks has not been modelled at radii where planets actually form. Gas
can significantly affect accretion onto giant planets, dampen eccentricities of
terrestrial planets, and cause planetary migration. While typically gas is assumed
to trace the dust, this assumption may not be appropriate because the excitation
level of molecular hydrogen, the primary constituent of the gas in disks, is
sensitive to FUV radiation, and accretion onto CTTSs produces large amounts of FUV
radiation, particularly in Ly-alpha. Results of this excitation are clearly seen in
STIS observations of CTTSs, which show strong molecular hydrogen fluorescence. We
have available a C++ code that solves for the excitation of molecular hydrogen as a
function of the UV radiation field, temperature, and gas density. We propose to
modify this code from its present state to apply to disks around young stars. With
these models and observations of the Ly-alpha and the FUV radiation fields, we will
attempt to explain existing spectra of molecular hydrogen in the UV and the IR. We
will also develop diagnostics to discriminate between disks and shocks and determine
photodissociation and photoevaporation timescales of the gas in the disk. These
results will significantly improve the understanding of the properties of gas at
radii and evolutionary period when planets are forming. This work will form a part
of Mr. Herczeg's PhD thesis.
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                                                9930(  1) - 04/04/03 10:21  - [  2]

            Summary Form for Proposal  9930

  Item                         Used in this proposal
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  Proposal Category            AR
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