Nebulae surrounding isolated Pop I WR stars provide observational constraints on as yet poorly determined chemical surface abundances and FUV energy distributions of their central stars. An integral of the mass loss history and the chemical evolution is stored in those parts of the nebulae that have suffered only very little mixing with the ISM (cf. Kwitter 1984). Effective temperatures in the Lyman continuum region are reflected in the ionization structure of oxygen and sulfur (cf. Mathis 1982). For intrinsic problems involved refer to the papers cited above.

Being one of the brightest lines in emission in the optical region of Wolf-Rayet (WR) stars, the λ4686 line of He II has attracted the attention of many investigators (Sahade, 1958; Ganesh and Bappu, 1967). Here, the binaries with subgroup WN components have been chosen, with periods ranging from 1.64d to 21.63d, for understanding the effect of the companion on the formation of this line.

A recently developed non-LTE code for realistic semi-empirical models of Wolf-Rayet atmospheres is used to calculate synthetic helium lines. From the resulting line strenghts it can be concluded that if He I lines are present, the effective temperatures of these stars have to be less than an upper limit. This limit depends on the stellar radius and is approximately 40kK for R* = 20 R⊙ to 60kK for R* = 5 R⊙.

The effects of using different treatments of the surface boundary conditions are investigated in the context of the mass of He White Dwarfs. We find that since the White Dwarf progenitor is a star with a very extended atmosphere, the results are sensitive to the degree of accuracy implemented in the handling of the boundary conditions.

HR 8752 is a G5 hypergiant in the Cep OBI association. It is an SRd variable according to the GCVS. The V and B-V curves of the star are plotted in Figure 1. One point in the figure is the mean of all measurements made in a ten-day interval. The circles contain the observations of Arellano Ferro (1985) which show large deviation in two cases. Neglecting these circles, it is clear from Figure 1 that HR 8752 has alternating brighter and fainter maxima, the difference between them being some hundredth of magnitude, A possible explanation will be outlined for this phenomenon.

The X-Ray (EXOSAT) and ultraviolet (IUE) observations of R Aqr and its jet are discussed in the light of a proposed model.

Optical spectroscopy is used to derive the electron temperature and density of the jet of R Aqr. We present polarimetric data which shows that the degree of polarization in R Aqr can vary by up to two orders of magnitude and that this variation is correlated with the phase of the Mira. The polarization angle also varies with the phase of observation.

R Aquarii is a very interesting symbiotic system. There is an emission nebulosity close to the star which extends in North-South direction and a “jet” feature of about 6″ with a position angle of 29° has also been observed (Sopka et al. 1982; Mauron et al. 1985; Kafatos et al. 1983). Polarization measurements are important to understand the peculiar geometry of the circumstellar material around the central objects. Wavelength and time dependence of polarization can be used to put constraints on the geometry of the object and to identify the mechanism(s) responsible for polarization. In view of this linear polarization measurements of R Aquarii were carried out by us in UBVRI bands. Observations were made during November-December 1984 on 1 meter telescope of Indian Institute of Astrophysics, Bangalore, with a dual channel photo polarimeter discussed elsewhere (Deshpande et al. 1985). Measured values of percent polarization and position angle at different phases alongwith the earlier observations of Serkowski (1974) and Ladbeck (1985) are plotted in Figure 1.

First results on the peculiar Mira variable star R Aquarii obtained by the Infrared Astronomical Satellite (IRAS) in the far-infrared region (12–100 microns) are presented. A simple radiative transfer model for plane, isothermal and homogeneous layer is given to interpret the far-infrared excess radiation in terms of circumstellar dust emission. A two dust shell model with silicate grains is proposed to explain the observed fluxes. This model explains as well the low-resolution spectra (LRS) in the 8–20 micron region from IRAS. The equivalent sizes of the emitting regions (shells) in R Aquarii are found to be 0.1 arc sec and 3 arc sec at temperatures of 800 ± 80 K and 87 ± 8 K respectively. Silicate grains of size 1 micron seem to be compatible with the observations. There is no clear indication for the presence of an isolated dust cloud in R Aquarii to support the eclipsing-cloud hypothesis for explaining the minima observed at 44 yr interval.

RX Puppis is a southern symbiotic star (R.A. 08h12m 28s.2, Dec. −41°33'18“ B1950). For almost a century it has been seen to have had a violent history at optical wavelengths. In 1974 it was discovered, at 5 GHz, to be a weak radio source. Shortly after, its radio spectrum was found to be of the optically thin type, having approximately the same flux density at all frequencies between 2.7 and 22 GHz. This implied that the RX Puppis system contained dispersed, ionized gas having a linear size >1015 cm.

The light variation of AG Dra is considered as a result of a variation of free-free emission from a gaseous envelope around the hot component. The emission measure of the envelope at a light maximum is estimated to be about Ne 2V = 6.5 × 1059 cm−3. The amplitude of the light variation in the U band should be less than 1.4 mag. which is consistent with the observed results. The emission measure of the envelope might vary according to a variation of mass transfer rate in an elliptical binary system.

We present the first results of an ongoing survey of the linear polarization properties of symbiotic stars. With these multifilter optical measurements, we aim to obtain a statistically significant sample from which to study the nature and geometrical arrangement of their circumstellar matter and its relationship to the stellar components. Up to now, the observations show.

CH Cyg is a binary (P∼5750 days) consisting of a normal M6-7 giant and an unseen companion. During active phase its spectrum is similar to that of a symbiotic star - the strong B-A continuum and numerous low-excitation emission lines dominate the visual and UV spectrum. The last outburst, started in 1977, is conspicuous by the highest brightness level observed since monitoring begun in 1935. In mid 1984, a drop in brightness was accompanied by large continuum and emission line changes and correlated with a radio outburst and two expanding jets appearance (Taylor et al. 1985).

R Aquarii is the closest symbiotic variable that shows extended emission with multiple jet components. A number of other symbiotics also show jet activity and this phenomenon may be common, particularly among D-type symbiotics.

KX And (HD 218393) belongs to well-known and often observed Be stars. The periodicity of spectroscopic characteristics as well as other observations led to the conclusion that the star is a peculiar interacting binary (Harmanec et al. 1980). The aim of this paper is to present the phase-dependent behaviour of the UV spectrum of the star.

We have observed 117 faint planetary nebulae in the J, H, K, and sometimes L and M bands. The objects are all listed in the Perek-Kouteck (PK) catalogue and were observed by IRAS.

In the course of a sensitive search for atomic hydrogen emission associated with planetary nebulae having high velocities relative to Galactic HI (Schneider et al. 1986), we detected absorption in the spectrum of IC 4997 (PK 58-10.1). This is only the second definite detection of HI associated with a PN. The velocity of the feature coincides precisely with that expected if the gas is expanding with the measured optical expansion velocity of 14 km s−1 (Sabbadin 1984), strongly suggesting an association.

The photometric behaviour of AGK3-0°965, the central star of the bipolar planetary nebula NGC 2346, has been monitored photometrically for several months at the Observatorio Astronómico Nacional at Tonantzintla and San Pedro Mértir, Mexico. A model is proposed in which the eclipses were caused by the passage of an elongated cool dust cloudlet of size ~ 2–5 × 1012 cm and total mass ~ 10−12 M⊙. This model can explain most of the observations. The velocity of the cloud in the direction of the major axis of the projected central binary orbit is vp = 0.14 km s−1. Another warmer (T ≲ 1000 K) circumstellar cloud is responsible for the infrared excess at wavelengths from 3 to 12 μm. Its emission, as seen from the Earth, has not changed significantly at λ > 3 μm during the past twelve years, as shown by new infrared observations also reported. Its most relevant physical properties are still to be determined. The present results provide the first evidence of a dense circumstellar cloudlet of mass similar to that of a minor planet which is probably the result of the fragmentation of a disk or toroid around the central star of NGC 2346. Although the presence of many other similar cloudlets in its vicinity is expected, the probability of similar events occurring in the next few hundred years is very small.

The details of the present work will be published in the Revista Mexicana de Astronomía y Astrofísica.

We report the first detection of millimeter CO emission in two highly evolved planetary nebulae: NGC 6720 and NGC 7293. The CO is a useful probe of the structure and kinematics of the molecular gas in the nebulae, and provides an estimate of the mass of material which remains un-ionized by the central star.

We obtained high resolution spectra of the red [NII]-lines in the bipolar nebula Mz-3, This object probably is a protoplanetary nebula (see e.g. Lopez and Meaburn, 1983 and Meaburn and Walsh, 1985). The spectra were taken in July and September 1982 at La Silla using the Coudé Auxiliary Telescope (CAT) combined with the Coudé Echelle Spectrograph (CES). The resolution depending on the slit width was 30000 and 100000, respectively. Fig. 1 shows the [NII]-lines at 6583.6 and 6548.3 Å together with Hα. The structure of the 6583.6 Å line, which is quite complicated in detail, is dominated by two narrow peaks, similar to the profiles of circumstellar O H-masers. The profile varies strongly with the slit width and shows substantial differences between the observations in July and September. - The most striking result of our observations is that the intensity ratio 6584/6548 deviates strongly from the canonical value of 3 as shown in Fig. 2.