CH Cyg was observed visually by Professor Władysław DziewulsKi in the years 1930–1940 at the Vilno Observatory, with the 15 cm refractor using Argelander’s method. As a sKillful and experienced observer he achieved the accuracy of his single measurement of about 0.05 mag. The series of his 652 estimates of CH Cyg has been recently reduced and is discussed in this paper.

Apparently in those years the star was in relatively quiet state (like in the years 1970–1977), when in the visual region the light of only the red giant component of this binary is visible. We deduce it from:

1. a) absence of any emission lines in spectra taKen by A. Joy in 1930 (Joy 1942)

2. b) visual brightness of the star almost never exceeding 7.0 mag. what is typical for the quiet state of pure M6III spectrum

3. c) red color, resulting from comparison of our visual brightnesses and the photographic ones published by S. Gaposchkin (1952)

Mikołajewski et al.(1987) quoted convincing arguments that CH Cygni is eclipsing binary system:

1. 1. Photometric minima in U light were separated by 57004÷5780 days which is very close to the spectroscopic period (P=5750±250d) found by Yamashita and Maehara (1979).

2. 2. Variations of Hβ and Hγ profiles during both minima can be succesfully interpreted as an eclipse of a rotating disk or envelope from which these profiles originate (see also Fernie et al.,1986).

3. 3. The flickering activity was absent during the 1985 minimum while observed before and after the minimum.

4. 4. Only forbidden lines were unaffected by the minimum. Recently, additional arguments for the eclipsing nature of CH Cygni have been found:

5. 5. Deep minimum in the IUE integrated flux was coincided with the minimum detected in U light (Mikołajewska et al., 1987a).

6. 6. Changes of Balmer decrement and Balmer continuum emission measure suggest a presence of relatively small dense region occulted during the minimum and extended low density region coinciding with the radio jets (Mikołajewska et al., 1987b).

7. 7. Radial velocity of the jet spatially resolved by Solf (1987) in the [OIII]5007 line suggests the jet is practically perpendicular to the line of sight.

In the period 1982–1986, new 98 radial velocities (RVs) were determined (at the figures denoted by □). All spectrograms were obtained at the Toruń Observatory. RVs were measured at the Skalnaté Pleso Observatory. The main results are summarized in the figures 1-3. The phase is determined from the middle position of the hot component eclipse (JD 2 446 272) and from the minima difference observed in U light curve (5700d) (Mikolajewski et al., 1987).

Slow changes of the RVs of the absorption components of ionized metals reflect the orbital motion of the hot component only between the phases 0.7 and 0.0. The rapid changes are observed mainly between the phases 0.8 and 0.9. They are created by combination of the emission red wing with the absorption component (Skopal et al., 1987). RVs of the cool component are in antiphase (Tomov and Luud, 1984).

The period of maximum brightness of CH Cygni which started in mid 1981 finished at the end of July 1984, when sudden drop by about 1 mag was observed (Fig.1). At the same time a radio outburst has occured and the jet structure has developed (Taylor et al.1986). The Toruń Observatory has recorded the spectra of CH Cygni just at this moment. Significant spectral variations, especially development of wide wings in Balmer emission lines have been found (Mikołajewski and Tomov 1985).

Mikołajewski et al. (1987) showed that the “shell” absorption lines roughly reflect the orbital motion of a hot companion of the M giant. Figure 1 presents radial velocities of these absorption lines of ionized and neutral metals (mainly TiII, FeI) together with the v.rad. followed from possible orbital solution suggested by Mikołajewski et al. About 3-4 days after the drop started the RVs of the “shell” absorption lines very quickly (during 3 days) got out of a deep local minimum (ΔV ∼15–20 km/s) preceding the drop by a mounth. The FeII emission lines, which are formed in the outer regions, do not show so large radial velocity variations ( Fig.1 ).

The spectacular changes of CH Cyg spectrum during the last period of activity and the flickering in short wavelength light suggest the possibility of rapid line variations (Walker et al.,1969). In November 1982 a series of spectral observations has been accomplished at Rozhen Observatory to investigate the subject.

In that period the spectrum of CH Cyg is dominated by type A shell lines. They are supposed to originate in an accretion disk surrounding the hot star of the binary system. The flickering in the optical wavelengths is characteristic for CH Cyg during periods of activity. Evidently it is related with the mass transfer. The investigation of its origin and relations with the other observational characteristics of the star could elucidate the accretion mechanism in this system.

Our wide-band polarimetric observations of CH Cyg began in 1974 and continued In 1976 and 1984. During the first two observational seasons the star was in quiet phase between two outbursts, in 1984 the latest outburst that began in 1977 was declining. Figure shows mean values of the degree of polarization P and the position angle θ for the different observational periods. Standard errors calculated by photon noise statistics are 0.02–0.04% for P and 1–5% for θ.

In 1974 (October 12 - December 1) polarization parameters did not change significantly. Sharp increase of the degree of polarization in the shortwave region of the spectrum and change with wavelength of the degree of polarization are typical for many cool luminous stars and indicate existence of an asymmetric circumstellar envelope around CH Cyg. Interstellar polarization in the direction of CH Cyg should be quite small [1,2],as its distance is 330 pc and colour-excess EB-V does not exceed 0.07m.

Following the discovery of the radio outburst and jet formation from CH Cygni in 1984, continued radio monitoring has been carried out with the Very Large Array. We present the preliminary results of these observations, including a high resolution image of the jet in 1986 – 1.5 years after the initial outburst. The star has remained active in the radio, undergoing at least one additional outburst. The radio jet has continued to expand and shows evidence of multiple episodes of ejection along the same axis.

The most spectacular episode in the history of CH Cyg was undoubtedly a sudden drop of brightness (by about 1 mag) during the last weak of July 1984, coinciding with the ejection of two collimated jets (Taylor et al. 1985) perpendicular to the line of sight (Solf 1987) and the orbital plane (Luud et al. 1986). Supercritical accretion cannot be responsible for the jet ejection mechanism, because the luminosity of the accreting component was always about 2 orders of magnitude lower than the Eddington limit (Mikolajewska et al. 1987). This mechanism is also inconsistent with the rapid drop of brightness coinciding with the ejection of material. Simultaneously, it is conspicuous that the increase of brightness to optical maximum was also rapid (∼1 mag from July to September 1981; e.g. Kaler et al. 1983).

The spatially resolved nebula that characterizes the D–type symbiotic R Aquarii has afforded investigators a unique opportunity to probe the extended emission line regions. Its extensive and complex radio morphology, that includes SiO emission from the only symbiotic associated with maser emission, has provided important clues concerning the mass expulsion process in interacting binary radio stars. Infrared, radio, optical, UV and X-ray observations of the system are discussed in context with models which have been proposed to explain the appearance of the brilliant jet.

The UV spectrum of the peculiar star RX Puppis has afforded symbiotic star investigators a wealth of information for unraveling its mysteries. RX Pup and R Aqr, both being of the D-type variety, are now better understood as result of an extended coverage of observations at different wavelengths including radio observations using the VLA. These stars present challenges to our understanding of the symbiotic phenomenon and clues to other astrophysical phenomena like jets. Resolution of the question whether RX Pup has a jet system and an associated system of rings/extended disk or, alternatively, a colliding winds region will be resolved by high resolution radio observations or future observations using the Hubble Space Telescope.

The dust-rich (D-type) symbiotic stars appear always to comprise a mira variable and a star of temperature ∼ 105 K which ionizes the mira’s circumstellar envelope. On timescales of decades they change little, save for the slow pulsation of the mira at infrared wavelengths. RX Puppis is a striking exception to this generalization, however, since it undergoes extraordinary changes.

RX Pup drifts between two extremes, exhibiting intermediate states. Table I summarises the known characteristics in the extreme states. Because of its variability, models of RX Pup are more highly constrained, giving us a chance to understand one of the D-type symbiotics.

Optical spectra of RX Pup from the Anglo-Australian Telescope. Tie breadth of the lines in 1976 may be due to lower spectral resolution.

Symbiotic star AG Peg (HD 207757), which is still declining from the outburst in the last century, appears to be related to the very slow RT Serpentis type novae: binary stars consisting of a cool M giant and a hot component, which underwent outburst.

AG Peg was ninth magnitude star before the year 1850. Then it slowly rised in brightness and reached fifth magnitude in 1885. After the sudden drop of brightness in 1892 due to the dust formation in expanding envelope, the star returned to the sixth magnitude and then it was continuously decreasing in brightness (Lundmark, 1921; Rigollet, 1947; Belyakina, 1968). Nowadays the decrease of brightness is 0.021 mag/yr (Fernie, 1985).

The light curves in UBVRI and profiles of the emission lines of Hα, HeII 5411 and HeI 5876, 6678 obtained during 1985–87. The radial velocities of the emission lines HeI 6678 and HeII 5411 demonstrated clear periodic variations in antiphase with the radial velocity defined for the absorption line.

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.

It can be shown that the long–term periodic variations in the U band, distinctly observed in AG peg by UBV photometry (Belyakina 1970) from the early 1960’s with amplitude increasing, over since, have in fact two principal reasons for their existence. One of these is transparency of the envelope to the Lc-emission of the hot component in AG Peg arisen in the 1950’s and increasing since then. The second one is connected with the changes of the transparency of the compact part of the gas envelope located close to the hot component when in moves along its orbit (Yudin 1987). It is interesting to note that for the orbital solution with non-zero eccentricity (Hunchings et al. 1975) the transparency minimum and consequently the flux emission maximum for the gas envelope in AG Peg are observed in the moment when the hot component is close to its apoastron. The amplitude of the periodic variations in V increases due to the existence in AG Peg of the effect of noticeable heating of the cool component’s hemisphere facing its hot companion. Using the TiO bands in the red the cool component in AG Peg is classified as slightly earlier than M2 from illuminated side and slightly later than M3 from the opposite one (Ipatov and Yudin 1986).

Symbiotic star AG Peg consists of a hot subdwarf with a WN6 spectrum and a cool M3 giant, which is not filling its Roche lobe (Boyarchuk 1967, 1985). A detailed study of profiles, equivalent widths and radial velocities of emission lines in optical spectra allowed Hutchings et al. (1975) to conclude that a hot subluminous star approximately 1 M⊙ rotates rapidly and ejects material which streams towards the cool M giant with the mass 3-4 M⊙. UV observations seems to support this model.

UV observations provided from the databank of the IUE satellite were obtained in 1978–81 by different observers. The observational material consists of 12 high dispersion SWP spectra and covers the region 1200 – 2100 A. The spectra were reduced at Trieste observatory using standard IUESIPS package. The radial velocities of emission lines were measured on tracings and corrected for the motion of Earth and satellite.

Precise cross-correlation absorption-line velocities have been derived using high resolution near infrared coude’ spectra for the symbiotic nova AG Pegasi. A revised weighted orbital solution is presented based on both extant photographic and the new absorption-line velocities.

A small number of symbiotic stars are characterized by a single nova-like outburst with a very slow time evolution and several years of permanence at maximum. We describe in detail RR Tel and discuss the main properties of these objects.

Since 1979 a team consisting of T.S.Belyakina, N.I.Bondar’, K.K.Chuvaev, Yu.S.Efimov, R.E.Gershberg, V.I.Krasnobabtsev, E.P.Pavlenko, P.P.Petrov, I.S.Savanov, N.I.Shakhovskaya, N.M.Shakhovskoj, A.G.Shcherbakov and V.I.Shenavrin from the Crimea, Dr. V.Piirola from Finland and Drs D.Chochol, L.Hric and J.Grygar from Czechoslovakia are carrying out a coordinated study of pecular Kuwano-Honda (PU Vul) object, and this short report is made on behalf of the team.

PU Vul flared up from 14m to 9m in 1978 and up to date maintains the high brightness. Our studies include the optical and IR photometry, spectroscopy, spectrophotometry, polarimetry and UV observations with the space station Astron. The general character of brightness variations and time distribution of our observations are given in Fig.1.

Evidence for formation and subsequent expansion of an A–F supergiant envelope in the very slow symbiotic nova PU Vul caused by quasiperiodic injections of matter from M giant to the A–F supergiant is given.