The hybrid Nova Vul 2024 (=V615 Vul)

¹ ANS Collaboration, c/o Astronomical Observatory, 36012 Asiago (VI), Italy
² INAF National Institute of Astrophysics, Astronomical Observatory of Padova, 36012 Asiago (VI), Italy
³ Dept. of Physics and Astronomy, University of Padova, Asiago Astrophysical Observatory, 36012 Asiago (VI), Italy

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 19 October 2025
Accepted: 16 February 2026

Abstract

Context. Among galactic novae, many remain poorly characterized due to heterogeneous data, observational challenges, or heavy reddening along the Galactic plane. A detailed characterization is particularly crucial for novae exhibiting peculiar features, such as those belonging to the hybrid class.

Aims. We present the spectroscopic and photometric evolution of the heavily reddened Nova Vul 2024 (=V615 Vul) from discovery on 29 July 2024 to well into its nebular phase.

Methods. We obtained daily optical, absolute-fluxed spectroscopy in both low- and high-resolution echelle modes, providing a detailed account of the spectral evolution. Photometric data were primarily sourced from AAVSO, while refined astrometry was performed to assess the positional coincidence with a potential progenitor. Robust determinations of t₃ and E_B − V were achieved, allowing for the application of the Maximum Magnitude–Rate of Decline (MMRD) relation; the resulting distance is in excellent agreement with 3D Galactic extinction maps.

Results. Nova Vul 2024 is a very fast nova (t₃ = 10.7 ± 0.5 d) located at a distance of 5.0 ± 1.0 kpc, suffering from a large reddening (E_B − V= 1.6 ± 0.1). Around maximum light, it exhibited a Fe II-type spectrum with very broad emission lines (FWZI ≈ 5800 km s⁻¹) and high-velocity P-Cygni absorptions. Following t₃, coinciding with the emergence of hard X-ray emission, the nova displayed pronounced photometric oscillations primarily driven by continuum variations. Simultaneously, He/N features developed alongside Fe II lines, classifying V615 Vul as a rare hybrid nova. During the nebular phase, the ionization level increased, reaching [Fe VII] and likely [Fe X]. The ejecta showed no neon overabundance and expanded ballistically, as indicated by the constant widths, profiles, and castellation of the high-resolution emission lines.