Mitsuhiko Honda et al. 2006 ApJ 646 1024 doi:10.1086/505035
Mitsuhiko Honda1,2,3, Hirokazu Kataza1, Yoshiko K. Okamoto4, Takuya Yamashita2,3, Michiel Min5, Takashi Miyata6, Shigeyuki Sako7, Takuya Fujiyoshi2, Itsuki Sakon3 and Takashi Onaka3
Show affiliationsWe have obtained 8-13 μm spectra of 30 young (1-10 Myr) low-mass pre-main-sequence stars using COMICS on the 8.2 m Subaru Telescope to examine dust evolution in protoplanetary disks. Most spectra show silicate emission features of various strengths and shapes, indicative of dust processing during the different stages of protoplanetary disk evolution. We have analyzed the observed silicate emission features using a simple model previously applied to the more massive and luminous Herbig Ae/Be systems. We determined the feature strength and shape and derived the composition and typical size of the silicate dust grains. We confirm the previously reported dependency of the silicate feature strength and shape on the grain size of the amorphous silicate dust. We examine the relation between the derived dust properties and stellar and circumstellar disk parameters, such as systemic age, luminosity of Hα (LHα), disk mass, and opacity power-law index β at radio wavelengths. A possible relation is found between silicate feature strength (grain size indicator) and the LHα, which may be an indicator of accretion activity. It implies that the turbulence induced by accretion activity may be important for grain size evolution in the disk. No clear correlation between the crystallinity and the stellar/disk parameters is found. We find that on average 5%-20% in mass of the silicate dust grains is in crystalline form, irrespective of systemic age. This latter finding supports the idea that crystalline silicate is formed at an early evolutionary phase, probably at the protostellar phase, and is remaining during the later stages.
circumstellar matter; dust, extinction; stars: pre-main sequence
Issue 2 (2006 August 1)
Received 2005 November 25, accepted for publication 2006 April 11
Mitsuhiko Honda et al. 2006 ApJ 646 1024
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