Meridional flows in the disk around a young star

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Abstract

Protoplanetary disks are known to possess a variety of substructures in the distribution of their millimetre-sized grains, predominantly seen as rings and gaps1, which are frequently interpreted as arising from the shepherding of large grains by either hidden, still-forming planets within the disk2 or (magneto-)hydrodynamic instabilities3. The velocity structure of the gas offers a unique probe of both the underlying mechanisms driving the evolution of the disk—such as movement of planet-building material from volatile-rich regions to the chemically inert midplane—and the details of the required removal of angular momentum. Here we report radial profiles of the three velocity components of gas in the upper layers of the disk of the young star HD 163296, as traced by emission from 12CO molecules. These velocities reveal substantial flows from the surface of the disk towards its midplane at the radial locations of gaps that have been argued to be opened by embedded planets4,5,6,7: these flows bear a striking resemblance to meridional flows, long predicted to occur during the early stages of planet formation8,9,10,11,12. In addition, a persistent radial outflow is seen at the outer edge of the disk that is potentially the base of a wind associated with previously detected extended emission12.

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Fig. 1: Rotation maps and the inferred 3D geometry of the disk.
Fig. 2: Measured velocity structure of the gas in the disk around HD 163296.
Fig. 3: Schematic of the meridional flow.
Fig. 4: Hydrodynamical simulations of meridional flows.

Data availability

This paper makes use of the following ALMA data: ADS/JAO.ALMA#2013.1.00366.S, ADS/JAO.ALMA#2013.1.00601.S and ADS/JAO.ALMA#2016.1.00484.L. The raw data are available from the ALMA archive (http://almascience.nrao.edu/aq/), while the imaged data and scripts are available from the DSHARP website (https://bulk.cv.nrao.edu/almadata/lp/DSHARP/). The Python packages used for the analysis of the data are available via their GitHub repositories: bettermoments (https://github.com/richteague/bettermoments) and eddy (https://github.com/richteague/eddy).

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Acknowledgements

This paper makes use of the following ALMA data: ADS/JAO.ALMA#2013.1.00366.S, ADS/JAO.ALMA#2013.1.00601.S and ADS/JAO.ALMA#2016.1.00484.L. ALMA is a partnership of the European Southern Observatory (ESO; representing its member states), the National Science Foundation (NSF; USA) and the National Institutes of Natural Sciences (Japan), together with the National Research Council (Canada), the National Science Council and the Academia Sinica Institute of Astronomy and Astrophysics (Taiwan), and the Korea Astronomy and Space Science Institute (Korea), in cooperation with Chile. The Joint ALMA Observatory is operated by ESO, Associated Universities, Inc./National Radio Astronomy Observatory (NRAO), and the National Astronomical Observatory of Japan. The NRAO is a facility of the NSF operated under cooperative agreement by Associated Universities, Inc. R.T and E.A.B. acknowledge funding from NSF grant AST-1514670 and NASA grant NNX16AB48G. J.B. acknowledges support from NASA grant NNX17AE31G, and computing resources provided by the NASA High-End Computing (HEC) Program through the NASA Advanced Supercomputing (NAS) Division at Ames Research Center and by the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by NSF grant number ACI-1548562.

Author information

R.T. devised the method and analysed the data. J.B. ran the hydrodynamic simulations. All authors wrote the manuscript and were participants in the discussion and interpretation of results, determination of the conclusions and revision of the manuscript.

Correspondence to Richard Teague.

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Competing interests

The authors declare no competing interests.

Extended data figures and tables

Extended Data Fig. 1 A comparison of emission heights inferred for the 12CO emission.

The grey points in the background represent individual measurements following ref. 15, while the red contour shows the Gaussian process model of this surface including 1σ uncertainties, as described in ref. 6. Grey lines are random samples from the parametric fit derived from modelling the line-of-sight velocity map, with their spread demonstrating the 1σ uncertainties. The dust gap locations5,28 (D10 to D145) and radial location of the velocity perturbation found7 in 12CO, the ‘CO kink’, are marked. The major axis of the beam is shown for scale at bottom right.

Extended Data Fig. 2 Measured velocity structure of HD 163296.

Top row, projected rotation velocity vϕ,proj; second row, the residual from the 10th-order polynomial fit to vϕ to highlight the small-scale structure; third row, the vR values; and fourth row, the deviation in the shifted and aligned line centre from the systemic velocity. Left and right columns show results using the parametric and non-parametric emission surface, respectively. Velocities in the lower three rows have been corrected for projection effects assuming i = 47.6°. Blue error bars show the inferred velocities assuming both vR and vϕ components, while red error bars assume vR = 0 m s−1.

Extended Data Fig. 3 Measured velocity structure of the gas in the disk around HD 163296.

a, b, As Fig. 2 but using the non-parametric emission surface to deproject the data. Structure in the emission height outside 3″ is due to higher noise in the data, as described in the text.

Extended Data Fig. 4 Gas temperature and sound speed.

The figure shows the derived gas temperature (Tgas, top panel) and the derived gas sound speed (cs, bottom panel) as a function of radius. Error bars show the 1σ uncertainty. The drop in these values in the inner ~30 au (shaded area) is due to beam dilution.

Extended Data Fig. 5 Impact of the choice of velocity baseline.

The figure shows how the choice of vϕ,mod affects the residuals from vϕ, as in the second row of Extended Data Fig. 2. The top panel shows the different underlying models compared to the unprojected data, while the bottom panel shows the residual between the model and the observations. Regardless of the vϕ,mod chosen, the structure in δvϕ = (vϕ − vϕ,mod)/vϕ persists.

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Teague, R., Bae, J. & Bergin, E.A. Meridional flows in the disk around a young star. Nature 574, 378–381 (2019) doi:10.1038/s41586-019-1642-0

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