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Post Info TOPIC: Z Andromedae


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Title: Measuring the orbital inclination of Z Andromedae from Rayleigh scattering
Authors: A. Skopal, N. Shagatova

The orbital inclination of the symbiotic prototype Z And has not been established yet. At present, two very different values are considered, i ~ 44 degrees and i >~ 73 degrees. The correct value of i is a key parameter in, for example, modelling the highly-collimated jets of Z And. The aim of this paper is to measure the orbital inclination of Z And. First, we derive the hydrogen column density (nH), which causes the Rayleigh scattering of the far-UV spectrum at the orbital phase phi = 0.961 plus/minus 0.018. Second, we calculate nH as a function of i and phi for the ionisation structure during the quiescent phase. Third, we compare the nH(i,phi) models with the observed value. The most probable shaping of the HI/HII boundaries and the uncertainties in the orbital phase limit i of Z And to 59 -2/+3 degrees. Systematic errors given by using different wind velocity laws can increase i up to ~74 degrees. A high value of i is supported independently by the orbitally related variation in the far-UV continuum and the obscuration of the OI] 1641 A emission line around the inferior conjunction of the giant. The derived value of the inclination of the Z And orbital plane allows treating satellite components of H-alpha and H-beta emission lines as highly-collimated jets.

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Title: The symbiotic system Z Andromedae : a spectral analysis of the anomalous 1984-1986 outburst
Authors: M. Contini

The visual magnitude profile of the symbiotic system Z And during the 1984-1986 activity period appears double peaked and the flux intensity is low compared to outbursts in other epochs. The detailed modelling of the observed spectra, accounting for the shells ejected by the red giant star, shows that the outburst is intrinsically single but distorted by the collision at different phases of the white dwarf wind with two close shells.

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ZAndb.gif
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The symbiotic variable star Z Andromedae is in outburst.
The star is currently at magnitude 9.0

The cataclysmic variable star is a prototype for symbiotic variables (ZANDs). The system consists of a primary white dwarf and a secondary M giant star.

Apparent magnitude: (V) 10.53
Max magnitude: 8
Spectral type: M6.5

Position (2000): RA 23h 33m 39.9505s, Dec +48 49' 05.947"

light curve

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Title: Activity cycle of the giant star of Z Andromedae and its spin period
Authors: Elia M. Leibowitz, Liliana Formiggini (The Wise Observatory-Tel Aviv University-Israel)

We have reanalysed the long-term optical light curve (LC) of the symbiotic star Z Andromedae, covering 112--yr of mostly visual observations. Two strictly periodic and one quasi-periodic cycles can be identified in this LC. A P1=7550 d quasi periodicity characterizes the repetition time of the outburst episodes of this symbiotic star. Six such events have been recorded so far. During quiescence states of the system, i.e. in time intervals between outbursts, the LC is clearly modulated by a stable coherent period of P2=759.1 d. This is the well known orbital period of the Z And binary system that have been measured also spectroscopically. A third coherent period of P3=658.4 d is modulating the intense fluctuations in the optical brightness of the system during outbursts. We attribute the trigger of the outbursts phenomenon and the clock that drives it, to a solar type magnetic dynamo cycle that operates in the convection and the outer layers of the giant star of the system. We suggest that the intense surface activity of the giant star during maximum phases of its magnetic cycle is especially enhanced in one or two antipode regions, fixed in the atmosphere of the star and rotating with it. Such spots could be active regions around the North and the South poles of a general magnetic dipole field of the star. The P3 periodicity is half the beat of the binary orbital period of the system and the spin period of the giant. The latter is then either 482 or 1790 d. If only one pole is active on the surface of the giant, P3 is the beat period itself, and the spin period is 352 d. It could also be 5000 d if the giant is rotating in retrograde direction. We briefly compare these findings in the LC of Z And to similar modulations that were identified in the LC of two other prototype symbiotics, BF Cyg and YY Her.

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Z Andromedae (HD 221650) is a symbiotic variable star with an hourglass shaped nebula (like the Homonculus Nebula or Supernova 1987A).

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Spectral type: M6.5
Magnitude range 8.4 - 11.5 V


Z Andromedae

Position(2000): RA 23h 33m 39.9505 Dec +48 49' 05.947''

Z Andromedae.kmz
Google Sky File (1 kb, kmz)



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