Effect of MHD Wind-driven Disk Evolution on the Observed Sizes of Protoplanetary Disks

The Astrophysical Journal, vol. 926, pp. 61

Abstract

Abstract It is still unclear whether the evolution of protoplanetary disks, a key ingredient in the theory of planet formation, is driven by viscous turbulence or magnetic disk winds. As viscously evolving disks expand outward over time, the evolution of disk sizes is a discriminant test for studying disk evolution. However, it is unclear how the observed disk size changes over time if disk evolution is driven by magnetic disk winds. Combining the thermo-chemical code DALI with the analytical wind-driven disk-evolution model presented in Tabone et al., we study the time evolution of the observed gas outer radius as measured from CO rotational emission (R CO,90%). The evolution of R CO,90% is driven by the evolution of the disk mass, as the physical radius stays constant over time. For a constant α DW , an extension of the α Shakura–Sunyaev parameter to wind-driven accretion, R CO,90% decreases linearly with time. Its initial size is set by the disk mass and the characteristic radius R c,0, but only R c,0 affects the evolution of R CO,90%, with a larger R c,0 resulting in a steeper decrease of R CO,90%. For a time-dependent α DW , R CO,90% stays approximately constant during most of the disk lifetime until R CO,90% rapidly shrinks as the disk dissipates. The constant α DW models are able to reproduce the observed gas disk sizes in the ∼1–3 Myr old Lupus and ∼5–11 Myr old Upper Sco star-forming regions. However, they likely overpredict the gas disk size of younger (⪅0.7 Myr) disks.

Authors 4

1. Leon Trapman corresponding

   University of Wisconsin–Madison

   Affiliation as printed

   Department of Astronomy, University of Wisconsin-Madison, 475 N Charter Street, Madison, WI 53706, USA; ltrapman@wisc.edu

   Department of Astronomy, University of Wisconsin-Madison, 475 N Charter Street, Madison, WI 53706, USA

2. Benoît Tabone Aachen Leiden Observatory

   Leiden University · Leiden Observatory

   Affiliation as printed

   Leiden Observatory, Leiden University, 2300 RA Leiden, The Netherlands

3. Giovanni P. Rosotti Aachen Leiden Observatory

   Leiden University · University of Leicester · Leiden Observatory

   Affiliation as printed

   Leiden Observatory, Leiden University, 2300 RA Leiden, The Netherlands

   School of Physics and Astronomy, University of Leicester, Leicester, LE1 7RH, UK

4. Ke Zhang

   University of Wisconsin–Madison

   Affiliation as printed

   Department of Astronomy, University of Wisconsin-Madison, 475 N Charter Street, Madison, WI 53706, USA; ltrapman@wisc.edu

   Department of Astronomy, University of Wisconsin-Madison, 475 N Charter Street, Madison, WI 53706, USA