The Impact of Accretion Disk Winds on the Optical Spectra of Cataclysmic Variables

TL;DR

This study uses Monte Carlo simulations to show that accretion disk winds in cataclysmic variables significantly influence their optical spectra, affecting emission lines and continuum features, especially at high inclinations.

Contribution

It demonstrates that standard and higher-density disk wind models can reproduce key optical spectral features and may explain observed single-peaked emission lines in CVs.

Findings

Wind models produce observable optical emission lines like Hα and He II λ4686.

Higher-density winds can fill in the Balmer jump, matching observations.

Denser winds can generate single-peaked Hα emission lines.

Abstract

Many high-state non-magnetic cataclysmic variables (CVs) exhibit blue-shifted absorption or P-Cygni profiles associated with ultraviolet (UV) resonance lines. These features imply the existence of powerful accretion disk winds in CVs. Here, we use our Monte Carlo ionization and radiative transfer code to investigate whether disk wind models that produce realistic UV line profiles are also likely to generate observationally significant recombination line and continuum emission in the optical waveband. We also test whether outflows may be responsible for the single-peaked emission line profiles often seen in high-state CVs and for the weakness of the Balmer absorption edge (relative to simple models of optically thick accretion disks). We find that a standard disk wind model that is successful in reproducing the UV spectra of CVs also leaves a noticeable imprint on the optical spectrum, particularly for systems viewed at high inclination. The strongest optical wind-formed recombination lines are H$\alpha$ and He II $\lambda4686$. We demonstrate that a higher-density outflow model produces all the expected H and He lines and produces a recombination continuum that can fill in the Balmer jump at high inclinations. This model displays reasonable verisimilitude with the optical spectrum of RW Trianguli. No single-peaked emission is seen, although we observe a narrowing of the double-peaked emission lines from the base of the wind. Finally, we show that even denser models can produce a single-peaked H$\alpha$ line. On the basis of our results, we suggest that winds can modify, and perhaps even dominate, the line and continuum emission from CVs.