Ricci, L. and Trotta, F. and Testi, L. and Natta, A. and Isella, A. and Wilner, D. J. (2012) The effect of local optically thick regions in the long-wave emission of young circumstellar disks. Astronomy and Astrophysics, 540 . A6. ISSN 0004-6361 http://resolver.caltech.edu/CaltechAUTHORS:20120529-102755659
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Multi-wavelength observations of protoplanetary disks in the sub-millimeter continuum have measured spectral indices values which are significantly lower than what is found in the diffuse interstellar medium. Under the assumption that mm-wave emission of disks is mostly optically thin, these data have been generally interpreted as evidence for the presence of mm/cm-sized pebbles in the disk outer regions. In this work we investigate the effect of possible local optically thick regions on the mm-wave emission of protoplanetary disks without mm/cm-sized grains. A significant local increase of the optical depth in the disk can be caused by the concentration of solid particles, as predicted to result from a variety of proposed physical mechanisms. We calculate the filling factors and implied overdensities these optically thick regions would need to significantly affect the millimeter fluxes of disks, and we discuss their plausibility. We find that optically thick regions characterized by relatively small filling factors can reproduce the mm-data of young disks without requesting emission from mm/cm-sized pebbles. However, these optically thick regions require dust overdensities much larger than what predicted by any of the physical processes proposed in the literature to drive the concentration of solids. We find that only for the most massive disks it is possible and plausible to imagine that the presence of optically thick regions in the disk is responsible for the low measured values of the mm spectral index. For the majority of the disk population, optically thin emission from a population of large mm-sized grains remains the most plausible explanation. The results of this analysis further strengthen the scenario for which the measured low spectral indices of protoplanetary disks at mm wavelengths are due to the presence of large mm/cm-sized pebbles in the disk outer regions.
|Additional Information:||© 2012 ESO. Received 18 October 2011; Accepted 1 February 2012. Published online 14 March 2012. L.R. aknowledges the Ph.D. fellowship of the International Max-Planck-Research School. L.T. and F.T. acknowledge support from ASI under contract with INAF-Osservatorio Astrofisico di Arcetri. Support for CARMA construction was derived from the states of California, Illinois, and Maryland, the James S. McDonnell Foundation, the Gordon and Betty Moore Foundation, the Kenneth T. and Eileen L. Norris Foundation, the University of Chicago, the Associates of the California Institute of Technology, and the National Science Foundation. Ongoing CARMA development and operations are supported by the National Science Foundation under a cooperative agreement, and by the CARMA partner universities.|
|Subject Keywords:||protoplanetary disks|
|Official Citation:||The effect of local optically thick regions in the long-wave emission of young circumstellar disks L. Ricci, F. Trotta, L. Testi, A. Natta, A. Isella and D. J. Wilner A&A 540 A6 (2012) DOI: http://dx.doi.org/10.1051/0004-6361/201118296|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Jason Perez|
|Deposited On:||29 May 2012 18:30|
|Last Modified:||26 Dec 2012 15:16|
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