Padova-Asiago Supernova Group
Luminous Red Novae (LRNe)

One of the most spectacular transient phenomena induced by stellar binary interaction is the merging of two stars. The nature of LRNe, such as V838 Mon (Fig. 1), V4332 Sgr and M31-RV, was debated until V1309 Sco was discovered. A combination of spectroscopic data, along with a well-sampled light-curve, proved it to be a stellar merger (Tylenda et al. 2011, A&A, 528, 114; Mason et al. 2012, A&A, 544, 149).

Fig. 1 Expansion of the circum-stellar cocoon of LRN V838 Mon. Credits: NASA/ESA Hubble Space Telescope.

Although stellar mergers are common (de Mink et al. 2014, ApJ, 782, 7), only a handful of them have been discovered in the Milky Way and the Local Group. Recent discoveries of extragalactic counterparts (Blagorodnova et al. 2017, ApJ, 834, 107; Goranskij et al. 2016, AstBu, 71, 82, Smith et al. 2016, MNRAS, 458, 950) have extended the LRN zoo to much higher luminosities and masses. Common observables of these transients are their multi-peaked light curves (Fig. 2), and spectra that initially resemble those of type IIn SNe, then progressively develop a redder continuum to finally resemble those of M-type stars. In particular, late-time spectra show clear evidence of molecular bands (Fig. 3), which is an ubiquitous property of evolved LRNe.

Fig. 2 Quasi-bolometric light curves of a sample of extragalactic LRNe (from Pastorello et al. 2019a, A&A, 630, 75).

Fig. 3 Late spectra of a few LRNe, resembling those of M-type stars and showing bands of TiO and VO. The figure is from Pastorello et al. 2019a, A&A, 630, 75.

Leading researchers: A. Pastorello, E. Mason, V. Goranskij, E. Barsukova.

Main collaborators: M. Stritzinger, R. Kotak, E. Kankare, Y.-Z. Cai, N. Elias-Rosa, A. Morales-Garoffolo, P. Ochner, U. Munari (OAPd), A. Reguitti, G. Pignata, G. Valerin.