V1309 Scorpii: merger of a contact binary

Abstract

Context. Stellar mergers are expected to take place in numerous circumstences in the evolution of stellar systems. In particular, they are considered as a plausible origin of stellar eruptions of the V838 Mon type. V1309 Sco is the most recent eruption of this type in our Galaxy. The object was discovered in September 2008. Aims. Our aim is to investigate the nature of V1309 Sco. Methods. V1309 Sco has been photometrically observed in course of the OGLE project since August 2001. We analyse these observations in different ways. In particular, periodogram analyses were done to investigate the nature of the observed short-term variability of the progenitor. Results. We find that the progenitor of V1309 Sco was a contact binary with an orbital period of ∼1.4 day. This period was decreasing with time. The light curve of the binary was also evolving, indicating that the system evolved towards its merger. The violent phase of the merger, marked by the systematic brightenning of the object, began in March 2008, i.e. half a year before the outburst discovery. We also investigate the observations of V1309 Sco during the outburst and the decline and show that they can be fully accounted for within the merger hypothesis. Conclusions. For the first time in the literature we show from direct observations that contact binaries indeed end up by merging into a single object, as was suggested in numerous theoretical studies of these systems. Our study also shows that stellar mergers indeed result in eruptions of the V838 Mon type.

Period decrease in three SuperWASP eclipsing binary candidates near the short-period limit

“…He argues that mass may be ejected during a rapid phase of Roche-lobe overflow (or more generally, in a contact system) through L 2 , contributing to period decrease. Possible mechanisms for unstable mass transfer/loss leading to rapid period decrease in contact or near-contact binaries are also discussed in Rasio (1995), Tylenda et al (2011) andJiang et al (2012). This explanation is left as the most plausible for the observed period decreases in the objects J1743, J1331 and J2344, with further small contributions from magnetic braking and GWR.…”

“…Therefore our aim here was to determine whether any of the 53 candidate EBs showed evidence of period changes during their observation by SuperWASP. Period decreases might indicate a detached or semi-detached binary undergoing unstable mass transfer likely to end in merger, or even a contact binary approaching merger (as observed by Tylenda et al 2011). …”

The jet feedback mechanism (JFM) in stars, galaxies and clusters

“…They suggest that the ILOT V838 Mon was powered when a star swallowed three planets, one after the other (Retter et al 2006). The attribution of ILOTs to the CEE (or the onset of the CEE) but with a stellar companion followed with the ILOTs OGLE-2002-BLG-360 (Tylenda et al 2013), V1309 Sco (Tylenda et al 2011;Ivanova et al 2013a;Nandez et al 2014;Kamiński et al 2015), and M31LRN 2015(MacLeod et al 2016. Pejcha et al (2016a) and Pejcha et al (2016b) study mass loss through the second Lagrangian point L 2 or during a CEE, and found that about 5% of the kinetic energy is thermalized in the collision of equatorially ejected gas.…”

Dynamics of jets during the common-envelope phase

“…Thus, observational examples of CEs are scarce. Nonetheless, Tylenda et al (2011) and Tylenda & Soker (2006) have suggested that events like those observed in V1309 Sco and V838 Mon, among others, are the result of a CE leading to a merger. Also, MacLeod et al (2017) discussed a luminous red nova outburst in M31 as the onset of CE.…”