AAS 207th Meeting, 8-12 January 2006
Session 63 From Here to Eternity: The Spitzer Legacy Programs
Poster, Tuesday, 9:20am-6:30pm, January 10, 2006, Exhibit Hall

Previous   |   Session 63   |   Next  |   Author Index   |   Block Schedule

[63.52] Formation and Evolution of Planetary Systems: Upper Limits to the Gas Mass in Disks around Intermediate-Aged Solar-type Stars

J. Najita (NOAO), D. Hollenbach (NASA/Ames), U. Gorti (UC Berkeley), M. Meyer, J. S. Kim (Steward Observatory), P. Morris (Spitzer Science Center), I. Pascucci (Steward Observatory), J. Carpenter (Caltech), J. Rodmann (MPIA Heidelberg), T. Brooke, L. Hillenbrand (Caltech), E. Mamajek (CfA), D. Padgett (Spitzer Science Center), D. Soderblom (STScI), S. Wolf (MPIA Heidelberg), J. Lunine (LPL)

We report infrared spectroscopic observations of disks around nearby, intermediate-aged (3 Myr-300 Myr) solar-type stars. We have used the high spectral resolution mode (R~700) of the Infrared Spectrometer (IRS) aboard the Spitzer Space Telescope to search for gaseous emission lines from the disk. The observations reported here provide upper limits to the fluxes of the H2 S(0) 28\mum, H2 S(1) 17\mum, [FeII] 26\mum, [SiII] 35\mum, and [SI] 25\mum infrared emission lines.

The H2 line upper limits directly constrain the mass of warm molecular gas in the disk: typically M({\rm H2})< 5, 0.1 and 0.01 MJ 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 limits are considerably below the value for a minimum mass solar nebula, and indicate that less than 1 MJ of gas (at any temperature) exists in the 1-40 AU planet-forming region. Therefore, there is insufficient gas for giant planet formation to occur in these sources at this time. Either Jupiters have already formed or will never form. However, the models also indicate that if the inner disk radius is << 1 AU, then a considerable mass of cold gas could be present in the planet formation region of the disk without violating the line flux upper limits. This seems less likely because the gas would likely extend to the stellar surface, and viscous accretion onto the star would lead to observational indicators that are not observed.

Previous   |   Session 63   |   Next

Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.