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تسجيل مستخدم جديدNew outburst of the symbiotic nova AG Peg after 165 years
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AG Peg is known as the slowest symbiotic nova, which experienced its nova-like outburst around 1850. After 165 years, during June of 2015, it erupted again showing characteristics of the Z And-type outburst. The primary objective is to determine basic characteristics, the nature and type of the 2015 outburst of AG Peg. We achieved this aim by modelling the spectral energy distribution using low-resolution spectroscopy (330-750 nm), medium-resolution spectroscopy (420-720 nm; R=11000), and $UBVR_{rm C}I_{rm C}$ photometry covering the 2015 outburst with a high cadence. Optical observations were complemented with the archival HST and FUSE spectra from the preceding quiescence. During the outburst, the luminosity of the hot component was in the range of 2-11$times 10^{37}(d/0.8{rm kpc})^2$ erg/s. To generate the maximum luminosity the white dwarf (WD) had to accrete at $sim 3times 10^{-7}$ M$_{odot}yr^{-1}$, which exceeds the stable-burning limit and thus led to blowing optically thick wind from the WD. We determined its mass-loss rate to a few $times 10^{-6}$ M$_{odot}yr^{-1}$. At the high temperature of the ionising source, $1.5-2.3times 10^5$ K, the wind converted a fraction of the WDs photospheric radiation into the nebular emission that dominated the optical. A one order of magnitude increase of the emission measure, from a few $times 10^{59}(d/0.8 {rm kpc})^2$ cm$^{-3}$ during quiescence, to a few $times 10^{60}(d/0.8,{rm kpc})^2$ cm$^{-3}$ during the outburst, caused a 2 mag brightening in the LC, which is classified as the Z And-type of the outburst. The very high nebular emission and the presence of a disk-like HI region encompassing the WD, as indicated by a significant broadening and high flux of the Raman-scattered OVI 6825 AA line during the outburst, is consistent with the ionisation structure of hot components in symbiotic stars during active phases.
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Symbiotic stars often contain white dwarfs with quasi-steady shell burning on their surfaces. However, in most symbiotics, the origin of this burning is unclear. In symbiotic slow novae, however, it is linked to a past thermonuclear runaway. In June
2015, the symbiotic slow nova AG Peg was seen in only its second optical outburst since 1850. This recent outburst was of much shorter duration and lower amplitude than the earlier eruption, and it contained multiple peaks -- like outbursts in classical symbiotic stars such as Z And. We report Swift X-ray and UV observations of AG Peg made between June 2015 and January 2016. The X-ray flux was markedly variable on a time scale of days, particularly during four days near optical maximum, when the X-rays became bright and soft. This strong X-ray variability continued for another month, after which the X-rays hardened as the optical flux declined. The UV flux was high throughout the outburst, consistent with quasi-steady shell burning on the white dwarf. Given that accretion disks around white dwarfs with shell burning do not generally produce detectable X-rays (due to Compton-cooling of the boundary layer), the X-rays probably originated via shocks in the ejecta. As the X-ray photo-electric absorption did not vary significantly, the X-ray variability may directly link to the properties of the shocked material. AG Pegs transition from a slow symbiotic nova (which drove the 1850 outburst) to a classical symbiotic star suggests that shell burning in at least some symbiotic stars is residual burning from prior novae.
We present an analysis of the XMM-Newton observation of the symbiotic star AG Peg, obtained after the end of its 2015 outburst. The X-ray emission of AG Peg is soft and of thermal origin. AG Peg is an X-ray source of class beta of the X-ray sources a
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The nova outburst experienced in 2010 by the symbiotic binary Mira V407 Cyg has been extensively studied at optical and infrared wavelengths with both photometric and spectroscopic observations. This outburst, reminiscent of similar events displayed
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Optical spectroscopy study of the recent AG Peg outburst observed during the second half of 2015 is presented. Considerable variations of the intensity and the shape of the spectral features as well as the changes of the hot component parameters, cau
sed by the outburst, are discussed and certain similarities between the outburst of AG Peg and the outburst of a classical symbiotic stars are shown. It seems that after the end of the symbiotic nova phase, AG Peg became a member of the classical symbiotic stars group.
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