Abstract. The recent 1994-1995 active phase of AG Draconis has given us for the first time the opportunity to follow the full X-ray behaviour of a symbiotic star during two successive outbursts and to compare with its quiescence X-ray emission. With ROSAT observations we have discovered a remarkable decrease of the X-ray flux during both optical maxima, followed by a gradual recovering to the pre-outburst flux. In the UV the events were characterized by a large increase of the emission line and continuum fluxes, comparable to the behaviour of AG Dra during the 1980-81 active phase. The anticorrelation of X-ray/UV flux and optical brightness evolution is shown to very likely be due to a temperature decrease of the hot component. Such a temperature decrease could be produced by an increased mass transfer to the burning compact object, causing it to slowly expand to about twice its original size.
No abstract
Dissertation A directed by: Dr. WOLFGANG WENZEL. Sonneberg Date of graduation:1989 June 1For the period of the symbiotic nova AG Pegasi a number ofdifferent values ranging from 733 to 830 days was published. Knowledge of the correct period is necessary to calculate the orbital elements of a binary system. AG Peg had an outburst of about 3 mag in 1855. Since then its brightness is slowly decreasing and its spectrum underwent a radical change from Be after the outburst to a typical symbiotic spectrum (M3 + WN6). Additionally, the slope in magnitude is superimposed by small variations in brightness of about 0.S mag (in u ) with a period of about 800 days. The radial velocities of the spectral lines show variations with a cycle length of nearly the Same value.Analysis of all available observational data should find out the correct period and give an explanation for the differences in the periods published.The light curve composed by visual estimations and photoelectrical measurements shows a shortening of the period since 1975 from 827 to 760 days -a phenomenon difficult to explain.The photoelectric light curve from 1960 to 1985 provided a period of 812.6 days for the whole range of time, but different sections led to different values: 853, 803, and 747 days. From this we conclude that the photometric period is variable. The variation in brightness is not only caused by the orbital motion of the star, but also by other factors,The period determined by radial velocities of the absorption lines amounts to 829.5 days. This is in accordance with the period of the photographic light curve 1930 to 1981. We assume that this period is the correct orbital period of the binary system AG Pegasi, because it also agrees with the average of the photometric period (827 days) over a long time scale.Using the reduced radial velocity curve of the absorption lines, the following orbital elements of the M-star were determined:The radial velocities of the emission lines were reduced on the basis of this period. The amplitudes and phases regarding the absorption lines split the emission lines of AG Peg into three groups:
The photometric period of AG Pegasi has been determined to be 813 days on the basis of 165 photoelectrical observations from 1961 to 1986. When splitting the interval different periods were found.
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