The symbiotic system AG Draconis: Soft X-ray bremsstrahlung from the nebulae

Abstract

The modeling of UV and optical spectra emitted from the symbiotic system AG Draconis, adopting collision of the winds, predicts soft X-ray bremsstrahlung from nebulae downstream of the reverse shock with velocities > 150 km s −1 and intensities comparable to those of the white dwarf black body flux. At outbursts, the envelop of debris, which corresponds to the nebula downstream of the high velocity shocks (700-1000 km s −1 ) accompanying the blast wave, absorbs the black body soft X-ray flux from the white dwarf, explains the broad component of the H and He lines, and leads to low optical-UV-X-ray continuum fluxes. The high optical-UV flux observed at the outbursts is explained by bremsstrahlung downstream of the reverse shock between the stars. The depletion of C, N, O, and Mg relative to H indicates that they are trapped into dust grains and/or into diatomic molecules, suggesting that the collision of the wind from the white dwarf with the dusty shells, ejected from the red giant with a ∼1 year periodicity, leads to the U-band fluctuations during the major bursts.

Outburst activity of the symbiotic system AG Dra

“…The first outburst of this activity stage was one of the cool type and was followed by the fainter maximum of the hot type after 375 days. Contini & Angeloni (2011) mentioned that the collision of the wind from the white dwarf with the dusty shells, ejected from the red giant, leads to the fluctuations in U band during the major outburst. The long-term spectroscopic study of AG Dra was presented by Shore et al (2010).…”

The symbiotic system Z Andromedae : A spectral analysis of the anomalous 1984–1986 outburst

“…For lower velocities the SED in the soft X-ray range is the summed flux of bremsstrahlung from the nebulae and BB flux from the WD. The contribution to soft-X-rays up to the X-ray domain of bremsstrahlung from shocked nebulae was suggested for the symbiotic system AG Dra by Contini & Angeloni (2011).…”

“…Fragmentation of matter at the shock front produces dense clumps of gas and dust. Adopting C, N, O, and Si abundances lower than solar by a factor > 10 relative to H, as for AG Dra, (Contini & Angeloni 2011) would improve the fit of the Z And spectrum. However, there is no other evidence to justify this assumption.…”