Peculiarities of the Accretion Flow in the System HL CMa

TL;DR

This study analyzes the brightness variability of the dwarf nova HL CMa, revealing a consistent accretion flow geometry across states and estimating accretion parameters from multi-wavelength data.

Contribution

It introduces new insights into the variability suppression mechanisms and confirms the invariability of accretion flow geometry in HL CMa.

Findings

Variability suppression occurs above 7×10^{-3}Hz.

The accretion flow geometry remains unchanged during state transitions.

The boundary layer on the white dwarf is optically thick in all states.

Abstract

The properties of the aperiodic brightness variability for the dwarf nova HL CMa are considered. The variability of the system HL CMa is shown to be suppressed at frequencies above $7\times10^{-3}$Hz. Different variability suppression mechanisms related to the radiation reprocessing time, partial disk evaporation, and characteristic variability formation time are proposed. It has been found that the variability suppression frequency does not change when the system passes from the quiescent state to the outburst one, suggesting that the accretion flow geometry is invariable. It is concluded from the optical and X-ray luminosities of the system that the boundary layer on the white dwarf surface is optically thick in both quiescent and outburst states. The latter implies that the optically thick part of the accretion flow (disk) reaches the white dwarf surface. The accretion rate in the system, the flow geometry and temperature have been estimated from the variability power spectra and spectral characteristics in a wide energy range, from the optical to X-ray.