Paper: astro-ph/0605174
Date: Fri, 5 May 2006 20:22:54 GMT (153kb)

Title: Silicate Emission Profiles from Low-Mass Protostellar Disks in the Orion
Nebula: Evidence for Growth and Thermal Processing of Grains

Authors: R. Y. Shuping, Marc Kassis, Mark Morris, Nathan Smith, & John Bally

Comments: Accepted for publication in The Astrophysical Journal Letters.
Version with full quality figures can be obtained at:

http://homepage.mac.com/rshuping/Astro/docs/ProplydSilicates_ApJL2006.pdf
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We present 8--13 micron low resolution spectra (R~100) of 8 low-mass
protostellar objects ("proplyds") in the Orion Nebula using the Long Wavelength
Spectrometer (LWS) at the W. M. Keck Observatory. All but one of the sources in
our sample show strong circumstellar silicate emission, with profiles that are
qualitatively similar to those seen in some T Tauri and Herbig Ae/Be stars. The
silicate profile in all cases is significantly flattened compared to the
profile for typical interstellar dust, suggesting that the dominant emitting
grains are significantly larger than those found in the interstellar medium.
The 11.3-to-9.8 micron flux ratio--often used as an indicator of grain
growth--is in the 0.8 to 1.0 range for all of our targets, indicating that the
typical grain size is around a few microns in the surface layers of the
attendant circumstellar disk for each object. Furthermore, the silicate
profiles show some evidence of crystalline features, as seen in other young
stellar objects. The results of our analysis show that the grains in the
photoevaporating protostellar disks of Orion have undergone significant growth
and perhaps some annealing, suggesting that grain evolution for these objects
is not qualitatively different from other young stellar objects.

\\ ( http://arXiv.org/abs/astro-ph/0605174 , 153kb)