Models of the Hydrodynamic Histories of post-AGB Stars. I. Multiflow Shaping of OH231.8+04.2

TL;DR

This paper develops a hydrodynamic model of the preplanetary nebula OH231.8+04.2, explaining its complex structure and evolution over 100 years, based on detailed observations and simulations of flow interactions.

Contribution

It presents a physically justified hydrodynamic model that reproduces the nebula's structure, incorporating constraints from observations and exploring the impact of different flow parameters.

Findings

The nebula's shaping involves light flows with densities lower than the surrounding AGB wind.

Clumps and sprays of different speeds sculpt the nebula's axial flow and bulbs.

The ejected mass and momentum are large but can vary significantly across models.

Abstract

We present a detailed hydrodynamic model that matches the present structure of the well-observed preplanetary nebula OH231.8+04.2. The purpose of the model is to present a physically justified and coherent picture of its evolutionary history from about 100 years of the start of the formation of its complex outer structures to the present. We have adopted a set of initial conditions that are heavily constrained by high-quality observations of its present structure and kinematics. The shaping of the nebula occurs while the densities of the flows are "light": less than the surrounding AGB-wind environment. The simulations show that pairs of essentially coeval clumps and sprays of the same extent and density but different outflow speeds sculpted both the pair of thin axial flow "or spine" and the bulbs. The total ejected mass and momentum in the best fit model are surprisingly large -- 3 M_sun and 2.2 x 10^41 gm cm s-1, respectively -- however, these values are reduced by up to a factor of ten in other models that fit the data almost as well. Our ultimate goal is to combine the present model results of masses, momenta, flow speeds, and flow geometries for OH231 with those of other models to be published in the future in order to find common attributes of their ejection histories.