Astronomy and Astrophysics – Astrophysics
Scientific paper
Jul 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999a%26a...347l..43k&link_type=abstract
Astronomy and Astrophysics, v.347, p.L43-L46 (1999)
Astronomy and Astrophysics
Astrophysics
52
Stars: Binaries: Close, X-Rays: Stars, Stars: Evolution, Stars: White Dwarfs, Stars: Individual: U Scorpii
Scientific paper
BeppoSAX detected luminous 0.2-2.0 keV supersoft X-ray emission from the recurrent nova U Sco ~ 19-20 days after the peak of the optical outburst in February 1999. U Sco is the first recurrent nova to be observed during a luminous supersoft X-ray phase. Non-LTE white dwarf atmosphere spectral models (together with a ~ 0.5 keV optically thin thermal component) were fitted to the BeppoSAX spectrum. We find that the fit is acceptable assuming enriched He and an enhanced N/C ratio. This implies that the CNO cycle was active during the outburst, in agreement with a thermonuclear runaway scenario. The best-fit temperature is ~ 9x 10(5\) K and the bolometric luminosity (0.16-1.2)x 10(36) \ erg\ s(-1) \ (d/kpc)(2) . These values are in agreement with those predicted for steady nuclear burning on a WD close to the Chandrasekhar mass. The fact that U Sco was detected as a supersoft X-ray source is consistent with steady nuclear burning continuing for at least one month after the outburst. This means that only a fraction of the previously accreted H and He was ejected during the outburst and that the WD can grow in mass, ultimately reaching the Chandrasekhar limit. This makes U Sco a candidate type Ia supernova progenitor.
Hartmann H. W.
Kahabka Peter
Negueruela Ignacio
Parmar Arvind N.
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