Padova-Asiago Supernova Group
Luminous Red Novae (LRN) and other types of non-degenerate stellar mergers.

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 for these ILOTs are their multi-peaked light curve, and their spectra that progressively move from those of intermediate-type stars to M-type stars. In particular, late-time spectra show clear evidence of molecular bands (Fig. 2), which is one main properties of this type of transients.

Fig. 2 Late spectra of two LRNe and a M-type star, showing bands of TiO and VO. Credits: Figure from Blagorodnova et al. 2017, ApJ, 834, 107.

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

Collaborators: R. Kotak, E. Kankare, N. Blagorodnova.