WEAK TURBULENCE IN THE HD 163296 PROTOPLANETARY DISK REVEALED BY ALMA CO OBSERVATIONS
- Van Vleck Observatory, Astronomy Department, Wesleyan University, 96 Foss Hill Drive, Middletown, CT 06459 (United States)
- Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
- Department of Earth and Planetary Science, 307 McCone Hall, University of California, Berkeley, CA 94720 (United States)
- Department of Space Studies, Southwest Research Institute, Boulder, CO 80302 (United States)
Turbulence can transport angular momentum in protoplanetary disks and influence the growth and evolution of planets. With spatially and spectrally resolved molecular emission line measurements provided by (sub)millimeter interferometric observations, it is possible to directly measure non-thermal motions in the disk gas that can be attributed to this turbulence. We report a new constraint on the turbulence in the disk around HD 163296, a nearby young A star, determined from Atacama Large Millimeter/submillimeter Array Science Verification observations of four CO emission lines (the CO(3-2), CO(2-1), {sup 13}CO(2-1), and C{sup 18}O(2-1) transitions). The different optical depths for these lines permit probes of non-thermal line-widths at a range of physical conditions (temperature and density) and depths into the disk interior. We derive stringent limits on the non-thermal motions in the upper layers of the outer disk such that any contribution to the line-widths from turbulence is <3% of the local sound speed. These limits are approximately an order of magnitude lower than theoretical predictions for full-blown magnetohydrodynamic turbulence driven by the magnetorotational instability, potentially suggesting that this mechanism is less efficient in the outer (R ≳ 30 AU) disk than has been previously considered.
- OSTI ID:
- 22521943
- Journal Information:
- Astrophysical Journal, Vol. 813, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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