3D numerical simulations of photodissociated and photoionized disks

¹ Laboratório de Astrofísica Teórica e Observacional, DCET, Universidade Estadual de Santa Cruz, Rod. Ilhéus-Itabuna, km 16, Ilhéus, Bahia, Brasil
e-mail: mjvasc@uesc.br, hoth@uesc.br
² Instituto de Ciencias Nucleares, UNAM, Ap. Postal 70-543, CU, DF 04510, México
e-mail: raga@nucleares.unam.mx

Received: 23 September 2009
Accepted: 20 December 2010

Abstract

Aims. In this work we study the influence of the UV radiation field of a massive star on the evolution of a disklike mass of gas and dust around a nearby star. This system has similarities with the proplyds seen in Orion.

Methods. We study disks with different inclinations and distances from the source, performing fully 3D numerical simulations. We use the YGUAZÚ-A adaptative grid code modified to account for EUV/FUV fluxes and non-spherical mass distributions. We treat H and C photoionization in order to reproduce the ionization fronts and photodissociation regions observed in proplyds. We also incorporate a wind from the ionizing source, in order to investigate the formation of the bow shock observed in several proplyds. We examine density and Hα maps, as well as the mass loss rates in the photoevaporated winds.

Results. Our results show that a photoevaporated wind propagates from the disk surface and becomes ionized after an ionization front (IF) seen as a bright peak in the Hα maps. We follow the development of an HI region inside the photoevaporated wind which corresponds to a photodissociated region (PDR) for most of our models, except those without a FUV flux. For disks that are at a distance from the source d ≥ 0.1 pc, the PDR is thick and the IF is detached from the disk surface. In contrast, for disks that are closer to the source, the PDR is thin and not resolved in our simulations. The IF then coincides with the first grid points of the disk that are facing the ionizing photon source. In both cases, the photoevaporated wind shocks (after the IF) with the wind that comes from the ionizing source, and this interaction region is bright in Hα.

Conclusions. Our 3D models produce two emission features: a hemispherically shaped structure (associated with the IF) and a detached bow shock where both winds collide. A photodissociated region develops in all of the models exposed to the FUV flux. More importantly, disks with different inclinations with respect to the ionizating source have relatively similar photodissociation regions. If the disk axis is not aligned with the direction of the ionizing photon flux, the IF displays moderate side-to-side asymmetries, in qualitative agreement with images of proplyds, which also show such asymmetries. The mass loss rates are  ~10^-7   M_⊙ yr^-1 for face-on disks, and 5 × 10^-8 M_⊙ yr^-1 for inclined disks at distances from 0.1 to 0.2 pc from the ionizing photon sources.