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Published March 1, 2014 | Published + Submitted
Journal Article Open

Large-Scale Asymmetries in the Transitional Disks of SAO 206462 and SR 21


We present Atacama Large Millimeter/submillimeter Array (ALMA) observations in the dust continuum (690 GHz, 0.45 mm) and ^(12)CO J = 6-5 spectral line emission of the transitional disks surrounding the stars SAO 206462 and SR 21. These ALMA observations resolve the dust-depleted disk cavities and extended gaseous disks, revealing large-scale asymmetries in the dust emission of both disks. We modeled these disk structures with a ring and an azimuthal Gaussian, where the azimuthal Gaussian is motivated by the steady-state vortex solution from Lyra & Lin. Compared to recent observations of HD 142527, Oph IRS 48, and LkHα 330, these are low-contrast (≾ 2) asymmetries. Nevertheless, a ring alone is not a good fit, and the addition of a vortex prescription describes these data much better. The asymmetric component encompasses 15% and 28% of the total disk emission in SAO 206462 and SR 21, respectively, which corresponds to a lower limit of 2 M_(Jup) of material within the asymmetry for both disks. Although the contrast in the dust asymmetry is low, we find that the turbulent velocity inside it must be large (~20% of the sound speed) in order to drive these azimuthally wide and radially narrow vortex-like structures. We obtain residuals from the ring and vortex fitting that are still significant, tracing non-axisymmetric emission in both disks. We compared these submillimeter observations with recently published H-band scattered light observations. For SR 21 the scattered light emission is distributed quite differently from the submillimeter continuum emission, while for SAO 206462 the submillimeter residuals are suggestive of spiral-like structure similar to the near-IR emission.

Additional Information

© 2014 American Astronomical Society. Received 2013 December 10; accepted 2014 February 3; published 2014 February 14. We thank Takayuki Muto, Carol Grady, and Katherine Follette for providing the near-IR images, and we thank Wladimir Lyra for useful discussions. A.I., J.M.C., L.M.P acknowledge support from NSF award AST-1109334. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. This Letter makes use of the following ALMA data: ADS/JAO.ALMA 2011.0.00724.S. ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada) and NSC and ASIAA (Taiwan), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ. Facility: ALMA

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Published - 2041-8205_783_1_L13.pdf

Submitted - 1402.0832v1.pdf


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