Z Andromedae

Starbox begin
name=Z Andromedae Starbox image


caption = Z Andromedae Starbox observe
epoch=J2000
ra=23^h 33^m 39.9505^s
dec= +48° 49′ 05.947″
appmag_v=10.53
constell=Andromeda Starbox character
class=M6.5
b-v=1.1
u-b=
variable=symbiotic variable star Starbox astrometry
radial_v=3
prop_mo_ra=-6.72
prop_mo_dec= -6.21
parallax=2.34
p_error=2.91
absmag_v=11.88 Starbox detail
mass=0,6
radius=0,5
luminosity=0,04 | temperature=26000
metal=
rotation=
age=

Starbox catalog
names=EM* MWC 416, HIP 116287, SAO 53146, AG+48° 2087, GCRV 14773, IRAS 23312+4832, HV 193, AN 41.1901, JP11 3636, TYC 3645-2066-1, BD+48° 4093, GSC 03645-02066, 2MASS J23333994+4849059, AAVSO 2328+48, 2E 2331.6+4834, HD 221650, PLX 5697, 2E 4735, HIC 116287, PPM 64386. Starbox reference
Simbad=HD+221650
ARICNS =

Z Andromedae is a symbiotic variable star with an hourglass shaped nebula (like the Homonculus Nebula or Supernova 1987A) [ [http://www.aavso.org/vstar/vsots/1000.shtml AAVSO: Z And, October 2000 Variable Star Of The Month ] ] . It is the prototype for symbiotic variables, which are a subset of cataclysmic variables [ [http://www.daviddarling.info/encyclopedia/Z/Z_Andromedae_star.html Z Andromedae star ] ] . " " Our photometric observations of the symbiotic binary Z And during its recent (2000-2003) active phase revealed a minimum in the U, B and V light curves (LC) at the position of the inferior conjunction of its cool component (the orbital phase φ= 0). This fact and the behaviour of colour indices suggest that the minimum was due to the eclipse of the active hot object by the red giant. Physically plausible fit of the eclipse profile and a precise analysis of the spectral energy distribution (SED) in the ultraviolet continuum suggest a disk-like structure for the hot object during active phases. The present knowledge of fundamental parameters of the system limits the orbital inclination i to 76°-90°. " " - SKOPAL A.
" " The 0.06" separation between the peak of the extended emission and the central peak implies that the ejected material was moving with a velocity of at least ~ 200 - 300 km/s. The extended emission faded on a time scale of months. We discuss this possible jet in the context of other symbiotic jet sources, and compare our observations to previous radio maps of this source by H. Kenny. " " - SOKOLOSKI J.L.; BROCKSOPP C.; KAISER C.; SEYMOUR N.
" "Visual observations of the variable star Z And for the period 1993-1996 were analyzed from the perspective of dynamical systems theory. Background noise and signal detection were estimated by the use of an Autoregressive model and Singular Spectrum Analysis. The results suggest this time series possesses an attractor with a correlation dimension d_s=9.33±0.06." " - GALLEGO M.C., GARCIA J.A., VAQUERO J.M. and SANCHEZ-BAJO F.
" "The amplitude was typically 2-5 mmag, and it was correlated with the optical brightness during a relatively small outburst of the system. The most natural explanation is that the oscillation arises from the rotation of an accreting magnetic (BS{>~}105G) white dwarf." " - SOKOLOSKI J.L.; BILDSTEN L.
" "The Raman scattering process. At the initial stages of the outburst the hot object was characterized by the two-temperature spectrum (a warm stellar radiation and a strong nebular emission) with signatures of a mass-outflow at moderate (~100-200km/s) and very high (=~1000-2000km/s) velocities. The corresponding structure of the hot object consists of an optically thick, slowly-expanding disk-like material encompassing the accretor at the orbital plane and a fast optically thin wind over the remainder of the star. The disk-like shell persisted around the central star until 2002 August as was indicated by the eclipse effect. Then, a significant dilution of the optically thick material and evolution of a fast wind from the hot star, concentrated more at the orbital plane, were detected. A striking similarity of [FeVII] λ6087 and Raman λ6825 profiles at/after the dilution of the disk suggests their origin within the interaction zone where the winds from the binary components collide. " " - SKOPAL A., VITTONE A.A., ERRICO L., OTSUKA M., TAMURA S., WOLF M. and ELKIN V.G.

Combination nova

" "The 2 year long event had three distinct stages. During the first stage, the optical rise closely resembled an earlier, small outburst that was caused by an accretion disk instability. In the second stage, the hot component ejected an optically thick shell of material. In the third stage, the shell cleared to reveal a white dwarf whose luminosity remained on the order of 104 L{sun}for approximately 1 yr. The eruption was thus too energetic to have been powered by accretion alone. We propose that the initial burst of accretion was large enough to trigger enhanced nuclear burning on the surface of the white dwarf and the ejection of an optically thick shell of material. This outburst therefore combined elements of both a dwarf nova and a classical nova. Our results have implications for the long-standing problem of producing shell flashes with short recurrence times on low-mass white dwarfs in symbiotic stars. " " - SOKOLOSKI J.L., KENYON S.J., ESPEY B.R., KEYES C.D., McCANDLISS S.R., KONG A.K.H., AUFDENBERG J.P., FILIPPENKO A.V., LI W., BROCKSOPP C., KAISER C.R., CHARLES P.A., RUPEN M.P. and STONE R.P.S.

Activity cycle and its spin period

"Two strictly periodic cycles and one quasi-periodic cycle can be identified in this LC (light curve). 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, that is, 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 Andromedae binary system that has 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 outburst 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 Pole and the South Pole 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 a retrograde direction. We briefly compare these findings in the LC of Z Andromedae to similar modulations that were identified in the LC of two other prototype symbiotics, BF Cyg and YY Her." " - LEIBOWITZ E.M.; FORMIGGINI L

References

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* [http://aladin.u-strasbg.fr/AladinPreview?-c=23+33+39.9505%2B48+49+05.947&ident=V*+Z+And&submit=Aladin+previewer Image Z Andromedae]
* [http://www.aavso.org/charts/AND/Z_AND/ZAND-B.gifChart Z Andromedae]
* [http://www.aavso.org/images/zand.jpgChart Z Andromedae]
* [http://www.aavso.org/images/LTzand.gifview the long-term light curve of Z And]
* [http://www.aavso.org/vstar/vsots/1000.shtml www.aavso.org/]
* [http://webviz.u-strasbg.fr/viz-bin/VizieR-S?HIC%20116287 HIC 116287]
* [http://www.springerlink.com/content/h94v63g762038330/ A model for symbiotic star Z Andromedae]