Time Variability of the Inner Dust Rims in PMS Disk Systems

Details Time Variability of the Inner Dust Rims in PMS Disk Systems Time Variability of the Inner Dust Rims in PMS Disk Systems

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aas...211.5008s&link_type=abstract

American Astronomical Society, AAS Meeting #211, #50.08; Bulletin of the American Astronomical Society, Vol. 39, p.812

Astronomy and Astrophysics

Astronomy

Scientific paper

A decade-long program has revealed variability in the 1-5 micron emission in pre-main sequence disk systems. The variations in HD 31648 (MWC 480) and HD 163296 (MWC 275) are greatest near 3 microns, and the associated temperatures indicate that the variation must be occurring near the dust sublimation zone (DSZ) - the innermost wall of the dust disk. The silicate emission band partakes of the changes, indicating that small (less than a few microns) grains are present in this region. The variability may signal changes in the radial distance and scale height of the inner wall. Cyclic radial changes will promote annealing, sublimation, and re-condensation of grain material.
The variations die out rapidly at wavelengths longer than 11 microns, suggesting that the region just beyond the inner wall is shadowed. If there are changes in the scale height of the inner wall, the shadowing of the outer disk will change, possibly explaining the changing appearance observed in coronagraphic images of HD 163296.
In DG Tau, the silicate band is observed to transition between being in emission and absorption. The latter state requires dust be lofted above the disk, where both stellar and disk winds can transport it outward. The combination of grain processing and transport may explain the concentration of large crystalline material observed in the inner few AU of the disks, as well as the possibility of "salting" the comet-forming regions with this material.
The variability requires that surface brightness and interferometry observations should be accompanied by nearly-simultaneous spectral energy distribution observations, for proper interpretation.

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