# Far Ultraviolet Spectroscopy of Old Novae II: RR Pic, V533 Her and DI Lac

## TL;DR

This study analyzes FUV spectra of old novae RR Pic, V533 Her, and DI Lac, modeling their accretion disks and white dwarfs to understand their post-nova states and spectral features.

## Contribution

It provides detailed modeling of FUV spectra using high-resolution data, revealing the nature of accretion disks and white dwarfs in these old novae, with improved spectral coverage and reddening corrections.

## Key findings

- Accretion disks likely dominate the hot component in RR Pic and V533 Her.
- White dwarf photospheres are very hot and possibly larger than expected in RR Pic and V533 Her.
- DI Lac's spectrum best fits a low accretion rate disk with a 30,000K white dwarf.

## Abstract

The old novae V533 Her (Nova Her 1963), DI Lac (Nova Lac 1910) and RR Pic (Nova Pic 1891) are in (or near) their quiescent stage following their nova explosions and continue to accrete at a high rate in the aftermath of their explosions. They exhibit continua that are steeply rising into the FUV as well as absorption lines and emission lines of uncertain origin. All three have FUSE spectra which offer not only higher spectral resolution but also wavelength coverage extending down to the Lyman Limit. For DI Lac, we have matched these FUSE spectra with existing archival IUE spectral coverage to broaden the FUV wavelength coverage. We adopted the newly determined interstellar reddening corrections of Selvelli and Gilmozzi (2013). The dereddened FUV spectra have been modeled with our grids of optically thick accretion disks and hot, NLTE white dwarf photospheres. The results of our modeling analysis indicate that the hot component in RR Pic and V533 Her is likely to be the accretion disk with a mass accretion of $10^{-8}M_{\odot}$/yr and $10^{-9}M_{\odot}$/yr respectively. However, the disk cannot produce the observed absorption lines. For the WD to be the source of the absorption lines in these two systems, it must be very hot with a radius several times its expected size (since the WD in these systems is massive, it has a smaller radius). For DI Lac we find the best fit to be a disk with $\dot{M}=10^{-10}M_{\odot}$/yr with a 30,000K WD.