Query : 2016A&A...592A..49T

2016A&A...592A..49T - Astronomy and Astrophysics, volume 592A, 49-49 (2016/8-1)

Measuring turbulence in TW Hydrae with ALMA: methods and limitations.


Abstract (from CDS):

Aims. We aim to obtain a spatially resolved measurement of velocity dispersions in the disk of TW Hya.
Methods. We obtained images with high spatial and spectral resolution of the CO J=2-1, CN N=2-1 and CS J=5-4 emission with ALMA in Cycle 2. The radial distribution of the turbulent broadening was derived with two direct methods and one modelling approach. The first method requires a single transition and derives Tex directly from the line profile, yielding a vturb. The second method assumes that two different molecules are co-spatial, which allows using their relative line widths for calculating Tkin and vturb. Finally we fitted a parametric disk model in which the physical properties of the disk are described by power laws, to compare our direct methods with previous values.
Results. The two direct methods were limited to the outer r>40au disk because of beam smear. The direct method found vturb to range from ~=130m/s at 40au, and to drop to ~=50m/s in the outer disk, which is qualitatively recovered with the parametric model fitting. This corresponds to roughly 0.2-0.4cs. CN was found to exhibit strong non-local thermal equilibrium effects outside r ~= 140 au, so that vturb was limited to within this radius. The assumption that CN and CS are co-spatial is consistent with observed line widths only within r ≤ 100 au, within which vturb was found to drop from 100m/s (~=0.4cs) to zero at 100 au. The parametric model yielded a nearly constant 50m/s for CS (0.2-0.4cs). We demonstrate that absolute flux calibration is and will be the limiting factor in all studies of turbulence using a single molecule.
Conclusions. The magnitude of the dispersion is comparable with or below that predicted by the magneto-rotational instability theory. A more precise comparison would require reaching an absolute calibration precision of about 3%, or finding a suitable combination of light and heavy molecules that are co-located in the disk.

Abstract Copyright: © ESO, 2016

Journal keyword(s): techniques: interferometric - turbulence - methods: observational - ISM: kinematics and dynamics - submillimeter: ISM

VizieR on-line data: <Available at CDS (J/A+A/592/A49): list.dat fits/*>

Simbad objects: 6

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Number of rows : 6
N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2022
1 V* DM Tau Or* 04 33 48.7336763736 +18 10 09.973460280 14.30 14.82 14.00     M2Ve 586 0
2 EM* LkCa 15 Or* 04 39 17.7911622816 +22 21 03.390090984   13.01 12.03 11.61   K5:Ve 623 1
3 HD 31648 Ae* 04 58 46.2655706952 +29 50 36.987625680 7.84 7.78 7.62 7.76 7.43 A5Vep 464 0
4 QSO B1034-293 QSO 10 37 16.0795246848 -29 34 02.815459680   16.46 16.46 17.54   ~ 303 1
5 V* TW Hya TT* 11 01 51.9053285064 -34 42 17.033218380   11.94 10.50 10.626 9.18 K6Ve 1759 1
6 HD 163296 Ae* 17 56 21.2881851168 -21 57 21.871819008 7.00 6.93 6.85 6.86 6.67 A1Vep 976 0

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