Global axisymmetric simulations of photoevaporation and magnetically driven protoplanetary disk winds

Abstract

Context. Photoevaporation and magnetically driven winds are two independent mechanisms that remove mass from protoplanetary disks. In addition to accretion, the effect of these two principles acting concurrently could be significant, and the transition between them has not yet been extensively studied and quantified. Aims. In order to contribute to the understanding of disk winds, we present the phenomena emerging in the framework of twodimensional axisymmetric, nonideal magnetohydrodynamic simulations including extreme-ultraviolet (EUV) and X-ray driven photoevaporation. Of particular interest are the examination of the transition region between photoevaporation and magnetically driven wind, the possibility of emerging magnetocentrifugal wind effects, and the morphology of the wind itself, which depends on the strength of the magnetic field. Methods. We used the PLUTO code in a two-dimensional axisymmetric configuration with additional treatment of EUV and X-ray heating and dynamic ohmic diffusion based on a semi-analytical chemical model. Results. We determine that the transition between the two outflow types occurs for values of the initial plasma beta β ≥ 10 7 , while magnetically driven winds generally outperform photoevaporation for stronger fields. In our simulations we observe irregular and asymmetric outflows for stronger magnetic fields. In the weak-field regime, the photoevaporation rates are slightly lowered by perturbations of the gas density in the inner regions of the disk. Overall, our results predict a wind with a lever arm smaller than 1.5, consistent with a hot magnetothermal wind. Stronger accretion flows are present for values of β < 10 7 .

Global three-dimensional simulations of outer protoplanetary discs with ambipolar diffusion

“…There is very significant mass loss in our simulations, with d Ṁloss /d log R comparable or exceeding accretion rate. Such significant mass loss is generally expected in magneto-thermal disk winds (Bai et al 2016), where thermal pressure plays an important role and has been observed in a number of simulations of the kind (e.g., Bai & Stone 2017;Cui & Bai 2020;Rodenkirch et al 2020). On the other hand, the exact mass loss rate is sensitive to the thermal chemistry in the wind launching region, where our treatment is highly simplified, and more realistic simulations incorporating these physics tend to yield more mild mass loss rates (Wang et al 2019;Gressel et al 2020).…”

Wind–MRI interactions in local models of protoplanetary discs – I. Ohmic resistivity

“…We are also able to conduct simulations for longer and with lower β 0 values than Suzuki et al (2010), hence showing that the slanted symmetry state would eventually take over and change the wind behaviour, which was hinted at in their snapshots by the slightly slanted fields at the mid-plane, but were not fully developed to the extent that the cycles would be shut down and morph into the slanted steady wind, due to both their shorter run time and the very high β 0 value they used. Outburst behaviour was also observed in the initial stages of the Ohmic-only global simulations of Rodenkirch et al (2020) before settling of the disc to the slanted symmetry wind state, and it would be interesting to investigate to what extent the cyclic outburst behaviour we uncovered is also present in global discs.…”

“…Others (Gressel et al 2020) have suggested that it could be a manifestation of corrugation of the mid-plane by the vertical shear instability (VSI) (Urpin 2003;Urpin & Brandenburg 1998). However, settling to the slanted symmetry state was also observed in global simulations where Ohmic and ambipolar diffusion were the only non-ideal effects present (Gressel et al 2020), and even in purely Ohmic (Rodenkirch et al 2020) or ambipolar (Riols et al 2020) discs. The latter simulation is also locally isothermal, shutting down the VSI and ruling it out as necessary for the development of the slanted symmetry.…”

“…Another advantage of a local model is that we can explore a much wider parameter space and run simulations for much longer than global ones, allowing us to access the long-term outcomes of the wind. As slanted symmetry profiles have been reported even in simulations with only Ohmic resistivity (Rodenkirch et al 2020), we restrict the non-ideal physics we consider to Ohmic resistivity only, to identify the minimum ingredients required for the disc to adopt the different wind symmetries. While Hall drift and ambipolar diffusion also have significant impact on protoplanetary disc dynamics (Lesur et al 2014;Bai 2015), their anisotropic and nonlinear nature makes it much harder to isolate and evaluate their effects, and we relegate their study to a future work.…”

Dust entrainment in photoevaporative winds: Densities and imaging

“…While current literature agrees on two major scenarios that can drive disk winds -that is magnetics-and photoevaporation-driven outflows (see e.g. Owen et al 2010;Gressel et al 2015;Bai et al 2016;Wang et al 2019;Picogna et al 2019;Wölfer et al 2019;Rodenkirch et al 2020) -it remains unclear which mechanism dominates during which evolutionary stages (see e.g. Ercolano & Pascucci 2017;Coutens et al 2019;Gressel et al 2020).…”