Non-LTE Monte Carlo Radiative Transfer: II. Non-Isothermal Solutions for Viscous Keplerian Disks

TL;DR

This paper develops a comprehensive model for viscous Keplerian disks around hot stars, incorporating non-isothermal conditions and vertical hydrostatic equilibrium, revealing significant deviations from isothermal assumptions that impact spectral predictions.

Contribution

It presents the first self-consistent solution combining non-isothermal viscous diffusion with vertical hydrostatic equilibrium for Be star disks.

Findings

Non-isothermal models significantly differ from isothermal assumptions.

Temperature strongly influences the disk density structure.

Results impact spectral modeling of Be star disks.

Abstract

We discuss the basic hydrodynamics that determines the density structure of the disks around hot stars. Observational evidence supports the idea that these disks are Keplerian (rotationally supported) gaseous disks. A popular scenario in the literature, which naturally leads to the formation of Keplerian disks, is the viscous decretion model. According to this scenario, the disks are hydrostatically supported in the vertical direction, while the radial structure is governed by the viscous transport. This suggests that the temperature is one primary factor that governs the disk density structure. In a previous study we demonstrated, using 3-D NLTE Monte Carlo simulations, that viscous keplerian disks can be highly non-isothermal. In this paper we build upon our previous work and solve the full problem of the steady-state non-isothermal viscous diffusion and vertical hydrostatic equilibrium. We find that the self-consistent solution departs significantly from the analytic isothermal density, with potentially large effects on the emergent spectrum. This implies that non-isothermal disk models must be used for a detailed modeling of Be star disks.