SETI public: Formation and Evolution of Planetary Systems: Upper Limits the Gas Mass in HD105

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Paper: astro-ph/0506252
Date: Fri, 10 Jun 2005 22:13:27 GMT (77kb)

Title: Formation and Evolution of Planetary Systems: Upper Limits the Gas
Mass
in HD105

Authors: D. Hollenbach, U.Gorti, M.Meyer, J.S.Kim, P.Morris, J.Najita,
I.Pascucci, J.Carpenter, J.Rodmann, T.Brooke, L.Hillenbrand, E.Mamajek,
D.Padgett, D.Soderblom, S.Wolf, J.Lunine
Comments: To appear in the Astrophysical Journal
\\
We report infrared spectroscopic observations of HD 105, a nearby ($\sim 40$
pc) and relatively young ($\sim 30$ Myr) G0 star with excess infrared
continuum
emission, which has been modeled as arising from an optically thin
circumstellar dust disk with an inner hole of size $\gtrsim 13$ AU. We have
used the high spectral resolution mode of the Infrared Spectrometer (IRS) on
the Spitzer Space Telescope to search for gas emission lines from the disk.
The
observations reported here provide upper limits to the fluxes of H$_2$ S(0)
28$\mu$m, H$_2$ S(1) 17$\mu$m, H$_2$ S(2) 12 $\mu$m, [FeII] 26$\mu$m, [SiII]
35$\mu$m, and [SI] 25$\mu$m infrared emission lines. The H$_2$ line upper
limits directly place constraints on the mass of warm molecular gas in the
disk: $M({\rm H_2})< 4.6$, 3.8$\times 10^{-2}$, and $3.0\times 10^{-3}$
M$_J$
at $T= 50$, 100, and 200 K, respectively. We also compare the line flux
upper
limits to predictions from detailed thermal/chemical models of various gas
distributions in the disk. These comparisons indicate that if the gas
distribution has an inner hole with radius $r_{i,gas}$, the surface density
at
that inner radius is limited to values ranging from $\lesssim 3$ gm
cm$^{-2}$
at $r_{i,gas}=0.5$ AU to 0.1 gm cm$^{-2}$ at $r_{i,gas}= 5-20$ AU. These
values
are considerably below the value for a minimum mass solar nebula, and
suggest
that less than 1 M$_J$ of gas (at any temperature) exists in the 1-40 AU
planet-forming region. Therefore, it is unlikely that there is sufficient
gas
for gas giant planet formation to occur in HD 105 at this time.

\\ ( http://arXiv.org/abs/astro-ph/0506252 , 77kb)

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