The Unique Cataclysmic Variable V Sge is Increasing

The Unique Cataclysmic Variable V Sge is Increasing Its Accretion With a Doubling Timescale of 89 Years and Will In-spiral and Merge in the Year 2083 ± 16 Bradley E. Schaefer, Juhan Frank, Manos Chatzopoulos Louisiana State University V SGE IS A CATACLYSMIC VARIABLE (CV): Binary: White dwarf + Main sequence star, Roche lobe overflow Eclipsing binary Double-lined spectroscopic binary V SGE IS THE MOST EXTREME CV: MV = -2. 2 Stellar wind up to 2. 3 x 10 -5 M /year V SGE IS UTTERLY UNIQUE IN THE LOCAL GROUP: Mass ratio (Mcomp/MWD) is 3. 9 No other CV in Local Group is known with >1

V SGE IS IN-SPIRALING VERY FAST ★ ★ ★ Mcomp/MWD = 3. 9 Unstable Runaway Accretion = -2. 4 x 10 -10 days/cycle Orbit fast in-spiraling d. V/dt = -0. 84 ± 0. 10 mag/century Flux doubling timescale of 89 years Accretion rising exponentially

V SGE’s INEVITABLE FATE IS A MERGER ★ ★ ★ Orbit in-spirals, accretion increases exponentially Massive winds, common-envelope Dynamical instability culminates with transfer of ~2 M in the last week -Fast increase in brightness -Appearing like a supernova or nova ★ Final merger between WD and remaining core of companion -Time scale of one day or faster ★ Merger releasing huge amount of gravitational energy -System will brighten by more than a nova and less than a supernova -Peak brightness for mergers are expected to last perhaps a month -Estimates of peak magnitude must be approximate -Three greatly different methods give estimated Vpeak from -0. 7 to -5. 1 mag. -That is, V Sge at peak will appear roughly from Sirius-to-Venus in brightness ★ When single star system settles down, it will be a simple red giant -Degenerate C/O core, -Surrounded by a hydrogen burning layer -Surrounded by hydrogen-rich mantle

HOW TO CALCULATE THE YEAR OF THE MERGER ★ ★ Literature & all past experience: Not applicable. MESA: cannot work for this unique CV Analytic calculations: too complex for analytic solutions Semi-analytic solution: propagate system properties forward year-by-year to day-by-day

WHEN IS THE MERGER OF V SGE? 2083 ★ ★ ★ 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: 2083 ★ ★ 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