A long term spectroscopic and photometric study of the old nova HR Del

TL;DR

This study presents a long-term spectroscopic and photometric analysis of the old nova HR Del, revealing complex Hα line profiles, ongoing activity possibly due to residual thermonuclear burning, and orbital phase-dependent variations.

Contribution

It provides the first detailed long-term spectroscopic and photometric characterization of HR Del, highlighting the structure of the Hα line and the nature of its variability.

Findings

Hα line shows a narrow component from an accretion disk and broader wings from ejected material.

Photometric variations include orbital phase-dependent irradiation effects.

Persistent activity suggests ongoing thermonuclear processes.

Abstract

The Nova HR Del, discovered in 1967, was found to be exceptionally bright in the optical and UV during the whole lifetime of the IUE satellite (ending in 1996) and appears to be still extremely luminous today. The reason for this continuing activity is not clear; continuing weak thermonuclear burning might be involved. HR Del was thus monitored over several years, both in broad band photometry and spectroscopically in the H$\alpha$ spectral region. The profile of the H$\alpha$ line shows two components: a narrow, central component; and broader wings. The former is most easily understood as being due to an accretion disk, whose geometry might lead to it partly occulting itself. That component shows something like an S wave with an orbital phase dependance, suggesting that it could be due to a spot bright in H$\alpha$. The wide component must come from another region, with a probably non-negligible contribution from the material ejected during the 1967 outburst. Non-orbital variations of the H$\alpha$ equivalent width were found both on long and short time scales. Similar variations were found in the photometry, showing a component with a clear dependence on the orbital phase, but no obvious relation with the H$\alpha$ variations. The orbital part of the photometric variations can be explained by irradiation of the companion, while the properties of H$\alpha$ are explicable by the presence of an accretion disk and a spot bright in H$\alpha$.