An in-depth reanalysis of the alleged type Ia supernova progenitor Henize 2-428

Abstract

Context. The nucleus of the planetary nebula Hen 2-428 is a short orbital-period (4.2 h), double-lined spectroscopic binary, whosestatus as potential supernova type Ia progenitor has raised some controversy in the literature.Aims. Aiming to resolve this debate, we carried out an in-depth reanalysis of the system.Methods. Our approach combines a refined wavelength calibration, thorough line-identifications, improved radial-velocity measure-ments, non-LTE spectral modeling, as well as multi-band light-curve fitting. Our results are then discussed in view of state-of-the-artstellar evolutionary models.Results. Besides systematic zero-point shifts in the wavelength calibration of the OSIRIS spectra also used in the previous analysis ofthe system, we found that the spectra are contaminated with diffuse interstellar bands. Our Voigt-profile radial velocity fitting method,which considers the additional absorption of these diffuse interstellar bands, reveals significantly lower masses (M1 = 0.66 ± 0.11 Mand M2 = 0.42 ± 0.07 M ) than previously reported and a mass ratio clearly below unity. Our spectral and light curve analyses leadto consistent results, though, we find higher effective temperatures and smaller radii than previously reported. Moreover, we find thered-excess that was reported before, is merely an artifact of an outdated reddening law used in the previous work.Conclusions. Our work showed that blends of He ii λ 5412 Å with DIBs have led to an overestimation of the previously reporteddynamical masses of Hen 2-428. The merging event of Hen 2-428 will not be recognized as a supernova type Ia, but most likely leadto the formation of a H-deficient star. We suggest that the system was formed via a first stable mass transfer episode, followed bycommon envelope evolution, and is now composed of a post-early asymptotic giant branch star and a reheated He-core white dwarf.