Seminars at FGG

An overview to the interacting binary class of Symbiotic Stars and the ongoing 2008-09 outburst of the system CI Cyg

Speaker: Alessandro Siviero (INAF - Osservatorio Astronomico di Padova)

Date and time: 2009-07-08 11:00

We present an overview to the interacting binary systems knows as the name of Symbiotic Stars, in which a hot compact object (very often a White Dwarf) accretes material from a late type giant via stallar wing or Roche overflow. In particular we discuss about the early phases of the ongoing outburst that CI Cyg, a prototype of this class, is currently undergoing after thirty years of flat quiescence. The outburst started while the accreting WD was being eclipsed by the Roche-lobe filling M giant companion, and it was discovered during the egress phase on the second half of August 2008. The outburst reached peak V-band brightness in early October 2008 and has been characterized by amplitudes up to 1.9, in B band. At maximum V-band brightness, the outbursting WD had expanded to closely resemble an F3 II/Ib star, with M_V=-3.5, T_{eff} ~ 6900 K and R=28 R_{sun}. The high ionization emission lines ([NeV], [FeVII], HeII), so prominent in quiescence, disappeared, and only lower ionization lines (Balmer, HeI, SiII, FeII, [OI]) were visible. During the outburst, Balmer and HeI emission lines declined in equivalent width but increased in absolute flux. The output radiated by the hot component during the outburst corresponds to nuclear burning proceeding at a 2.10e{-8} M_{sun}/yr rate.