Eruptions of the V838 Mon type: stellar merger versus nuclear outburst models

Abstract

We discuss various models and scenarios proposed to explain the nature of the V838 Mon type eruptions. In this class of eruptive objects we include: M 31 RV (erupted in 1988), V4332 Sgr (erupted in 1994) and V838 Mon (erupted in 2002). We concentrate on three models: (i) thermonuclear runaway on an accreting white dwarf (nova-like event); (ii) He-shell flash in a post asymptotic giant branch star (born-again AGB); and (iii) merger of stars. We show that models (i) and (ii) cannot account for the majority of the observed properties of the objects. Most significantly, in both nuclear burning type models the object is expected to heat up before declining and fade as a very hot compact star. In the observed eruptions the objects declined as very cool giants or supergiants. We show that the stellar merger model can account for all the observed properties and conclude that presently this is the most promising model to explain the eruptions of the V838 Mon type.

The January 2015 outburst of a red nova in M 31

“…Many of them are best explained by binary star mergers (Tylenda & Soker 2006) and therefore are often referred to as stellar mergers or "mergebursts" (Tylenda et al 2011;Kochanek et al 2014). Common observational properties during the first months of the outburst are the initial slow decline and a spectrum changing towards a late-type supergiant phase with colours shifting to the red.…”

A molecular cloud within the light echo of V838 Monocerotis

“…Several different explanations of the eruption of V838 Mon have been proposed, which were critically discussed by Tylenda & Soker (2006). The most promising model appears to be that of a stellar collision followed by a merger (Soker & Tylenda 2003;Tylenda & Soker 2006).…”

“…The most promising model appears to be that of a stellar collision followed by a merger (Soker & Tylenda 2003;Tylenda & Soker 2006). A crucial point in establishing the nature of the outburst is to constrain the evolutionary status of the progenitor of V838 Mon.…”

The peculiar nova V1309 Scorpii/nova Scorpii 2008

“…However, should the red nova be explained by stellar merging phenomena, the maximum luminosity is not necessarily a stringent constraint. At the same time, V1309 Sco might represent a link (an intermediate case) between the two classes of symbiotic and red-novae, should the red-nova class be caused by a thermo-nuclear reaction on a small mass accreting white dwarf (Shara et al 2009; see also Iben & Tutukov 1992;and Shen et al 2009, for a discussion about CNe outburst on small mass accreting white dwarfs) rather than to stellar merging (Tylenda & Soker 2006, and reference therein). The most recent models (Shara et al 2009) for classical nova outburst on low mass white dwarf (∼0.5 M ) accreting at a low rate (a few 10 −11Ṁ /yr) predict that these type of novae will accumulate large amount of mass on the white…”