On the road to planets: T Tauri disk evolution

Details On the road to planets: T Tauri disk evolution On the road to planets: T Tauri disk evolution

Dec 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004phdt........28m&link_type=abstract

Ph.D dissertation, 2004. 147 pages; United States -- California: University of California, Los Angeles; 2004. Publication Numbe

Computer Science

1

Circumstellar Disks, Planets, T Tauri

Scientific paper

An investigation into T Tauri disk evolution, on both a microscopic and macroscopic scale, is presented. On a microscopic scale, I search for the presence of grain growth in the optically thick disks surrounding GG Tau and HK Tau. Observations that resolve the scattered light from these disks are used to measure the phase function of the scattered light. Comparison with Monte Carlo models allow constraints to be placed on the maximum grain size in the size distribution that is responsible for the observed scattered light morphology. A multi-wavelength analysis of the scattered light disk around GG Tau in the near-infrared (1-2 mm) finds that the dust is consistent with that expected from the ISM. At longer wavelengths, where you are sensitive to larger than ISM grain sizes, we start to find evidence for grain growth. Spatially resolved 11.8 mm images of the edge-on protoplanetary disk around HK Tau B, obtained at the Keck telescope, find evidence for dust grains on the order of 1.5-3 mm in size. This is significantly larger than grain sizes expected in the ISM, implying that grain growth has occurred.
On a macroscopic size scale, the inner AU of a sample of T Tauri binary stars, with separations ranging from 28-1120 AU, is probed using high resolution mid- infrared imaging. These observations increase the sample of spatially resolved binaries with mid-infrared measurements by a factor of 5. 10% of the class II stars in the sample, showing optically thick disk emission at 10 mm, do not appear to be currently accreting and have lower K - L colors than class II stars. We define these stars to be passive disk stars; the star shows evidence for a circumstellar disk at 10 mm, but the inner edge of the disk appears disrupted and material is not actively accreting onto the star. These observations provide strong support for the 'inside out' disk evolution scenario and suggest that disk evolution is a multi-timescale process that accelerates at larger radii. The timescale for inner disk clearing, constrained by the observations of passive disks (t ~ 10 5 yrs) is at least an order of magnitude larger than the next stage of disk evolution, where the disk color transitions between 1 < K - N < 2.

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