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Z Andromedae: Quiescence and Activity

Published online by Cambridge University Press:  12 April 2016

A. Cassatella ,
T. Fernandez-Castro  and
N. Oliversen
A. Cassatella
Affiliation:
IUE Observatory, ESA, P.O. Box 54065, 28080 Madrid, Spain
T. Fernandez-Castro
Affiliation:
Planetario de Madrid, Parque Tierno Galvan 28045 Madrid, Spain
N. Oliversen
Affiliation:
Astronomy Programs, Computer Sciences Corporation NASA Goddard Space Flight Center, Greenbelt, Maryland 20771, U.S.A.

Extract

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Z Andromedae, often considered as the prototype of symbiotic stars, experimented, after several years of quiescence, a small outburst in March-April 1984, followed by a larger one in September-October 1985. The imminence of a new activity phase was predicted by Viotti et al. (1982). Z And is, together with AG Draconis, the only symbiotic star observed both during quiescence and activity with the IUE satellite. The early photometric and spectroscopic history of Z And has been recently reviewed by Kenyon (1986).

The behaviour of Z And in the ultraviolet during quiescence has been studied by Fernåndez-Castro et al. (1988), on the basis of data obtained by the International Ultraviolet Explorer from 1978 to 1982. In that period of time, the UV continuum and the emission line fluxes varied quasiperidically with a period of about two years, in phase with the Hα variability found by Altamore et al. (1979), with the UBV photometry by Belyakina (1985) and also in agreement with the ephemeris given by Kenyon and Webbink (1984). The electron density derived from Si III/C III] flux ratio, also varied in phase with the UV flux. In particular, a correlation was found between the electron density variations, and the UV continuum flux at 2900 A. This fact, together with the presence of a Balmer jump in emission, indicates that the principal contributor at those wavelengths is nebular emission, mainly free-bound transitions.

Type
Session 3. Physics of Individual Objects
Information
International Astronomical Union Colloquium , Volume 103: The Symbiotic Phenomenon , 1988 , pp. 181 - 186
Copyright
Copyright © Kluwer 1988

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