U Scorpii 2010 outburst: a new understanding of the binary accretion disk and the secondary star
We present optical and near-infrared (NIR) spectroscopic observations of
<ASTROBJ>U Sco</ASTROBJ> 2010 outburst. From the analysis of lines
profiles we identify a broad and a narrow component and show that the
latter originates from the reforming accretion disk. We show that the
accretion resumes shortly after the outburst, on day +8, roughly when
the super-soft (SSS) X-ray phase starts. Consequently <ASTROBJ>U
Sco</ASTROBJ> SSS phase is fueled (in part or fully) by accretion and
should not be used to estimate m<SUB>rem</SUB>, the mass of accreted
material which has not been ejected during the outburst. In addition,
most of the He emission lines, and the He ii lies in particular, form in
the accretion flow/disk within the binary and are optically thick, thus
preventing an accurate abundance determination. A late spectrum taken in
quiescence and during eclipse shows Ca ii H&K, the G-band and Mg ib
absorption from the secondary star. However, no other significant
secondary star features have been observed at longer wavelengths and in
the NIR band.
Based on observations carried out at the European Southern Observatory,
under programs 084.A-9003 & 284.D-5041.Table 1 and Appendix A are
available in electronic form at <A
href="http://www.aanda.org">http://www.aanda.org</A>