The spectrum of the recurrent nova U Scorpii during the 1999 outburst (original) (raw)

A&A 387, 1013-1021 (2002)

Astronomical Observatory of Padova, Asiago Section, Osservatorio Astrofisico, 36012 Asiago (Vi), Italy

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Received: 10 May 2001
Accepted: 25 February 2002

Abstract

An optical spectrum covering the range λ λ_4300–6900 Å of the recurrent nova U Sco in outburst was taken on February 26th 1999, only 16 hours after maximum. Broad emission lines of H I, He I, N II, N III were seen on the spectrum, while the emission line of He II λ_4686 was not yet seen. The FWHM of the emission component of H_α was 8000 km s-1 and the FWZI was roughly 12000 km s-1. The emission line of H_α had blue (-3250 km s-1), central (+30 km s-1), and red (+2770 km s-1) peaks, among which the red one was the most prominent. A narrow absorption component of H_α_ blue-shifted by -4850 km s-1 was seen. The other prominent lines had a main emission peak red-shifted by km s-1 and a weak secondary peak blue-shifted by km s-1. Most of He I and N II lines were flanked by a narrow absorption component blue-shifted by about -4300 km s-1 which was a good clue for the detailed identification of these lines. These absorption components and some emission lines of N II faded very rapidly and nearly disappeared one day after our observation. The widths of the emission lines decreased with time. The radial velocities of three emission peaks of H_α_ were -1560 km s-1, +60 km s-1 and +1800 km s-1on March 14th, 17 days after maximum, when the blue one became stronger than the others. The helium abundance by the number of atom of the ejecta is estimated as N(He)/N(H) which is much lower than those found in previous works, and is not different from those of normal classical novae. Adopting the distance 6 kpc, the mass of the ejecta is estimated as .

Key words: stars: individual: U Sco / novae, cataclysmic variables

© ESO, 2002