The hybrid Nova Vul 2024 (=V615 Vul)

TL;DR

This paper presents comprehensive optical spectroscopy of Nova Vul 2024, revealing its hybrid nature, detailed ejecta properties, and distance estimates, contributing valuable insights into nova classifications and evolution.

Contribution

It provides the first detailed spectroscopic analysis of Nova Vul 2024, confirming its hybrid nature and offering refined estimates of its distance, reddening, and ejecta characteristics.

Findings

Nova Vul 2024 is a rare hybrid nova with Fe II and He/N features.

Ejecta expand ballistically with no neon overabundance.

Distance estimated at 5.0 +/- 1.0 kpc using maximum magnitude-rate decline relation.

Abstract

We present daily optical, absolute-fluxed spectroscopy of the heavily reddened Nova Vul 2024 (=V615 Vul), obtained in both low- and high-resolution echelle modes from discovery on 29 July 2024 through the nebular phase. Refined astrometry confirms the positional consistency with a potential progenitor. Reliable estimates of the decline time (t3=10.7 +/- 0.5 d) and reddening (E(B-V)=1.6 +/- 0.1) enabled the application of the Maximum Magnitude - Rate of Decline relation, yielding a distance of 5.0 +/- 1.0 kpc in excellent agreement with 3D Galactic extinction maps. Around maximum light, the nova displayed a Fe II-type spectrum with very broad emission lines (FWZI 5800 km s-1) and high-velocity P-Cygni absorptions. Shortly after t3, coincident with the onset of hard X-ray emission, it showed pronounced photometric oscillations driven mainly by continuum variations. At the same time, He/N features developed alongside Fe II lines, identifying V615 Vul as a rare hybrid nova. During the nebular phase, the ionization level increased up to [Fe VII] and likely [Fe X]. The ejecta show no evidence of neon overabundance and expand ballistically, as indicated by the constant line widths, stable profiles, and characteristic castellation of the high-resolution emission lines.