Binary Star V Sagittae Will Explode As a Very Bright

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Binary Star V Sagittae Will Explode As a Very Bright

V SAGITTAE WILL MERGE IN THE YEAR 2083 ± 16, BECOMING AS BRIGHT AS SIRIUS Bradley E. Schaefer, Juhan Frank, Manos Chatzopoulos Louisiana State University V SAGITTAE (V Sge) IS CURRENTLY AN INCONSPICUOUS FAINT STAR: Sagitta is the “Arrow” constellation, and the Arrow points at V Sge Vega Deneb SagiVa V Sge × Altair V SGE IS A CATACLYSMIC VARIABLE (CV): Binary: White dwarf + Main sequence star, Roche lobe overflow V SGE IS IN-SPIRALING FAST, VERY FAST V SGE IS THE MOST EXTREME CV: ~100X brighter than all other known CVs Incredibly massive stellar wind V SGE IS UTTERLY UNIQUE Mass ratio (Mcomp/MWD) is 3.9 No other CV in Local Group is known with >1 V SGE HAS A FAST SHRINKING ORBIT u Required for mass ratio >>1 u Orbital period since 1904 is decreasing fast u Brightness and accretion rate increasing with doubling time of 89 years V SGE’s INEVITABLE FATE IS A MERGER The in-spiral increases at an ever accelerating rate Mass will fall of the normal star, then be shot out as a fierce stellar wind The final death spiral will come to a cusp, with ~2 solar-masses falling in the last week or so. The ‘explosion’ will be somewhere between a nova and a supernova V Sge will appear as a sudden ‘guest star’, lasting roughly a month near peak brightness V SGE WILL APPEAR AS BRIGHT AS SIRIUS IN THE SKY Hard to get accurate estimates Best estimates give peak brightness in range from around Sirius to around Venus WHEN IS THE MERGER OF V SGE? 1 Mdot RLOF 0 2083 Mdot wind -1 -2 NOW -3 [Mdot] Msun/year -4 10 -5 Log -6 1900 1950 2000 2050 ★ Merger in the year 2083 ± 16 ★ This in-spiral year is robust on variations of all inputs and observed target measures ★ The ±16 year error bar is almost entirely from measurement uncertainties in the doubling time scale. CONCLUSIONS: ★ V Sge is in-spiraling very fast, now brightening at an accelerating rate ★ Merger in the year 2083 ± 16 ★ We will see a ‘new star’ appearing in Sagitta (the Arrow) ★ The ‘new star’ will be roughly as bright as Sirius or Venus.

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