Kessler-Silacci, J. E. and Dullemond, C. P. and Augereau, J.-C. and Merín, B. and Geers, V. C. and van Dishoeck, E. F. and Evans, N. J., II and Blake, G. A. and Brown, J. (2007) Probing protoplanetary disks with silicate emission: Where is the silicate emission zone? Astrophysical Journal, 659 (1). pp. 680-684. ISSN 0004-637X http://resolver.caltech.edu/CaltechAUTHORS:KESapj07a
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Recent results indicate that the grain size and crystallinity inferred from observations of silicate features may be correlated with the spectral type of the central star and/or disk geometry. In this paper, we show that grain size, as probed by the 10 μm silicate feature peak-to-continuum and 11.3 to 9.8 μm flux ratios, is inversely proportional to log Lsstarf. These trends can be understood using a simple two-layer disk model for passive irradiated flaring disks, CGPLUS. We find that the radius, R10, of the 10 μm silicate emission zone in the disk goes as (L*/L☉)^0.56, with slight variations depending on disk geometry (flaring angle and inner disk radius). The observed correlations, combined with simulated emission spectra of olivine and pyroxene mixtures, imply a dependence of grain size on luminosity. Combined with the fact that R10 is smaller for less luminous stars, this implies that the apparent grain size of the emitting dust is larger for low-luminosity sources. In contrast, our models suggest that the crystallinity is only marginally affected, because for increasing luminosity, the zone for thermal annealing (assumed to be at T > 800 K) is enlarged by roughly the same factor as the silicate emission zone. The observed crystallinity is affected by disk geometry, however, with increased crystallinity in flat disks. The apparent crystallinity may also increase with grain growth due to a corresponding increase in contrast between crystalline and amorphous silicate emission bands.
|Additional Information:||© 2007 American Astronomical Society. Received 2006 September 19; accepted 2006 December 13. Print publication: Issue 1 (2007 April 10). Support for this work was provided through contracts 1256316, 1224608, and 1230780 issued by the Jet Propulsion Laboratory, California Institute of Technology, under NASA contract 1407. Astrochemistry in Leiden is supported by a NWO Spinoza and NOVA grant and by the European Research Training Network, The Origin of Planetary Systems (PLANETS, contract HPRN-CT-2002-00308). The authors would like to thank the referee for many helpful comments and suggestions.|
|Subject Keywords:||circumstellar matter; infrared: ISM; ISM: lines and bands planetary; systems: protoplanetary disks; stars: formation; stars: pre-main-sequence|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Tony Diaz|
|Deposited On:||12 Jan 2009 20:07|
|Last Modified:||26 Dec 2012 10:36|
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