The spectral evolution and ejecta of recurrent nova U Sco in the 2010 outburst

Synoptic spectroscopic observations of the U Sco 2010 outburst from maximum light to quiescence as well as a contemporaneous X-ray observation are presented and analyzed. The X-ray spectrum 52 days after outburst indicates a hot source (kTbb ~ 70 eV). . Narrow line components from the irradiated companion atmosphere were observed in hydrogen and helium optical recombination lines. The formation of a nebular spectrum is seen for the first time in this class of recurrent novae, allowing a detailed study of the ejecta using photoionization models. Unusual [OIII] auroral-to-nebular line ratios were found and possible scenarios of their origin are discussed. The modeling of the emission line spectrum suggests a highly heterogeneous ejecta with mass around or above 3 x 10-6 Msun

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1×10 -12

2×10 -12

3×10 -12 ISCaIIK+H Hδ Hγ HeI4471 CIII4650+NIII4640+OII4649 OII4591 Hβ NII5679+NaI5686 ISNaID+HeI5876+NII5940 OI8446 HeI7065 Hα NII5001+HeI5015 FeII(49) (t-t0 ) = 0.9 d (t-t0 ) = 2.0 d (t-t0 ) = 9.0 d (t-t0 ) = 23 d0 2×10 -12

4×10 -12 6×10 -12 0. 0 6. 0 ×10 -14 1. 2 ×10 -13 1. 8 ×10 -13 HeII5412 HeII4686 HeII4200 Hε HeII8237 3500 4000 4500 5000 5500 6000 6500 7000 7500 8000 8500 wavelength(Å)0 3×10 -15 6×10 -15 9×10 -15 HeII4540 H8 HeII4199 NV4945 HeII4025 OVI5291 0 2×10 -16 4×10 -16 6×10 -16 (t-t0 ) = 75 d 0. 0 4. 0 ×10 -16 8. 0 ×10 -16 1. 2 ×10 -15 [OIII]5007 +4959 [NII]5755 [OIII]4363 [NeIII]3868 Hα+[NII]6548,83 (t-t0 ) = 51 d HeII4686 HeII5412 3500 4000 4500 5000 5500 6000 6500 7000 7500 8000 8500 wavelength (Å) 0. 0

5.0×10 -17 1. 0 ×10 -16 1. 5 ×10 -16 (t-t0 ) = 163 d -500 0 500 HeII 4686 velocity (km/s) -500 0 500 Hα 10 -4 10 -3 0.0 1 0. 1 10. 5 -10 1 Energy (keV) 0.0 1 0. 1 5×1 0 -3 0.0 2 0.0 5 0.5 -10 1 Energy (keV) Counts/s/keV Counts/s/keV 0.9 (a) (b) χ χ 10 -7 10 -6 10 -5 shell mass (Msun )353637 38 Hα log[L*](erg/s)353637 38 total