Wednesday, July 17, 2013

1307.4088 (Ondrej Pejcha)

Burying a Binary: Dynamical Mass Loss and an Optically-Thick Wind Explain the Candidate Stellar Merger V1309 Scorpii    [PDF]

Ondrej Pejcha
V1309 Sco is proposed to be a stellar merger and a common envelope transient based on the pre-outburst light curve of a contact eclipsing binary with a rapidly decaying orbital period. Using published data, I show that the period decay timescale P/Pdot of V1309 Sco decreased from ~1000 to ~170 years in less than about 6 years, which implies a very high value of second period derivative. I argue that this is incompatible with period-braking processes mediated by tides such as the Darwin instability and magnetic breaking, or with dynamical friction in a common envelope. Instead, I propose that V1309 Sco was observed during the onset of dynamical mass loss, which launches a wind that eventually obscures the system. The photosphere in the optically-thick wind expands as the mass-loss rate increases, explaining the ~200 day rise to optical maximum. The model yields the mass-loss rate of the primary star as a function of time and fits the observed lightcurve remarkably well. V1309 Sco is thus a prototype of a new class of stellar transients driven by dynamical mass loss. I discuss implications of these findings for stellar transients and other suggested common envelope events.
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