A Method for the Study of Accretion Disk Emission in Cataclysmic Variables I: The Model

TL;DR

This paper introduces a new spectrum synthesis method for modeling UV emission from accretion disks in cataclysmic variables, combining detailed disk and wind models to produce synthetic spectra that match observations.

Contribution

The paper presents a novel 2.5D modeling approach that integrates disk atmosphere and wind structures to simulate UV spectra of CVs, incorporating effects of system parameters.

Findings

Synthetic spectra match observed UV line profiles at high inclinations.

Accretion rate influences wind temperature and UV line intensity.

Primary mass significantly affects P-Cygni profiles.

Abstract

We have developed a spectrum synthesis method for modeling the UV emission from the accretion disk from cataclysmic variables (CVs). The disk is separated into concentric rings, with an internal structure from the Wade & Hubeny disk-atmosphere models. For each ring, a wind atmosphere is calculated in the co-moving frame with a vertical velocity structure obtained from a solution of the Euler equation. Using simple assumptions, regarding rotation and the wind streamlines, these 1D models are combined into a single 2.5D model for which we compute synthetic spectra. We find that the resulting line and continuum behavior as a function of the orbital inclination is consistent with the observations, and verify that the accretion rate affects the wind temperature, leading to corresponding trends in the intensity of UV lines. In general, we also find that the primary mass has a strong effect on the P-Cygni absorption profiles, the synthetic emission line profiles are strongly sensitive to the wind temperature structure, and an increase in the mass loss rate enhances the resonance line intensities. Synthetic spectra were compared with UV data for two high orbital inclination nova-like CVs - RW Tri and V347 Pup. We needed to include disk regions with arbitrary enhanced mass loss to reproduce reasonably well widths and line profiles. This fact and a lack of flux in some high ionization lines may be the signature of the presence of density enhanced regions in the wind, or alternatively, may result from inadequacies in some of our simplifying assumptions.