The 1999 Outburst of the Recurrent Nova U Scorpii

Abstract

The optical spectra of the recurrent nova U Sco obtained in five epochs 0.45-42.35 days after the 1999 outburst maximum are presented here. For the first time, an outburst spectrum of U Sco has been obtained as early as 0.45 days after maximum. The spectral evolution is broadly similar to the 1979 and 1987 outbursts. The mass of the ejected shell is estimated to be ~10-7 Msolar. Based on the Mg I b 5174 Å and the Fe I+Ca I 5270 Å absorption indices in the late-decline phase spectrum of day 42.35, we estimate the secondary to be a K2 subgiant star.