Far Ultraviolet Spectroscopy of Seven Nova-Like Variables

TL;DR

This study analyzes far ultraviolet spectra of seven nova-like variables to determine accretion rates, white dwarf characteristics, and flux contributions, providing insights into their evolutionary status.

Contribution

It offers the first detailed spectral analysis of multiple nova-like variables, estimating accretion rates and white dwarf properties using archival data and a synthetic spectral approach.

Findings

RW Tri has a low-mass white dwarf (~0.4 Msun) and an accretion rate of 6.3e-9 Msun/yr.

KR Aur's white dwarf has Teff=29,000K and contributes 18% to FUV flux.

Accretion disks dominate the FUV spectra of V425 Cas, HL Aqr, and V825 Her.

Abstract

We present the results of a multi-component synthetic spectral analysis of the archival far ultraviolet spectra of several key nova-like variables including members of the SW Sex, RW Tri, UX UMa and VY Scl subclasses: KR Aur, RW Tri, V825 Her, V795 Her, BP Lyn, V425 Cas and HL Aqr. Accretion rates as well as the possible flux contribution of the accreting white dwarf are included in our analysis. Except for RW Tri which has a reliable trigonometric parallax, we computed the distances to the nova-like systems using the method of Knigge (2006). Our analysis of seven archival IUE spectra of RW Tri at its parallax distance of 341 pc consistently indicates a low mass (0.4Msun) white dwarf and an average accretion rate, 6.3 E-9Msun/yr. For KR Aur, we estimate that the white dwarf has Teff=29,000K, log g = 8.4 and contributes 18% of the FUV flux while an accretion disk with accretion rate of 3 E-10Msun/yr at an inclination of 41 degrees, contributes the remainder. We find that an accretion disk dominates the far UV spectrum of V425 Cas but a white dwarf contributes non-negligibly with approximately 18% of the FUV flux. For the two high state nova-likes, HL Aqr and V825 Her, their accretion disks totally dominate with 1 E-9Msun/yr and 3 E-9Msun/yr, respectively. For BP Lyn we find an accretion rate of 1 E-8Msun/yr while for V795 Her, we find an accretion rate of 1 E-10Msun/yr. We discuss the implications of our results for the evolutionary status of nova-like variables.