Computer Science
Scientific paper
May 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007sptz.prop40104c&link_type=abstract
Spitzer Proposal ID #40104
Computer Science
Scientific paper
Most 1 Myr old stars are surrounded by circumstellar accretion disks that undoubtedly represent the formation sites of planetary systems. Based on Spitzer and ground-based surveys from near-infrared to submillimeter wavelengths, it is becoming increasingly clear that by an age of 10 Myr, the reservoir of primordial dust grains in disks has been drastically depleted over all orbital radii for more than 90% of solar type stars. However, these observations do not constrain the lifetime of the gas, whose evolution may be decoupled from the dust. The lifetime of gas in primordial circumstellar disks has fundamental consequences for the formation of Jovian planets, dynamical evolution of terrestrial planets, and migration of planetesimals and dust grains. In a recent Spitzer photometric survey of the 5 Myr Upper Sco OB association, we identified a population of 10 A- and B- type stars surrounded by circumstellar disks with large (> 10 AU) inner holes inferred from the dust component. These disks are at an advanced evolutionary stage relative to the optically-thick, gas-rich primordial disks found around Herbig Ae/Be stars, and may represent the latter stages in the dissipation of primordial disks or the formative stages of debris systems. Given the relative youth of Upper Sco, this sample represents an important population to establish the gas dissipation time scales around A- and B- stars. We propose to obtain IRS high resolution spectra of these 10 stars to search for gas emission lines from Ne II, Ne III, S, Fe II, and molecular hydrogen. By combining these observations with our complementary ground-based survey, we can search for gas over the entire disk and determine if these disks retain sufficient mass of gas to form Jovian planets, or whether we are observing an end-stage in primordial disk evolution that establishes an upper limit on the timescale to form gas-giant planets in A- and B-type stars.
Carpenter John
Dahm Scott
Gorti Uma
Hollenbach David
Patience Jenny
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