Burrell (1976) performed an abundance analysis of the southern R CrB star UW Cen and reported a metal deficiency by a factor of 660 compared to the sun. However, his analysis was made employing very uncertain gf values, which resulted in lower estimates for Texc and Tion etc. We have reanalysed his data using new values and model atmospheres calculated by Schönberner (1975). Our analysis shows that the star has nearly solar abundance.

The spectrophotometric observations obtained in the wavelength range 3400A to 8000A during 1974, 1972 minima of R CrB have been fitted with Mie scattering calculations assuming sperical graphite particles and various size distributions. Power law type distributions fit the observations fairly well, and indicate that there is decrease in mean particle size as the star comes out of minimum.

Fourier analysis of the light curves of RCrB in V band near maximum shows that in addition to several significant short periods there is a modulation of the visual light with a period around 1170 day, similar to that of L band flux, noticed by strecker. This indicates that there is some contribution to the visual light variations of the star from the pulsating circumstellar dust. Radial velocities of R CrB obtained at Kavalur during February-May 1985 show variations with a period around 47 days.

During light minimum phase, R CrB shows a broad emission line spectrum of He I including λ10830, λ7065, λ7281, λ3889, λ6678 and λ3188. But λ5876 is very weak. The observed intensity ratios of I(λ3889)/I(λ5876) and I(λ7065)/I(λ5876) were greater than 1. The anomalous intensities of these lines appear to be due to optical depth efects. Peliminary analysis is presented to derive the physical conditions of the emitting gas.

The circumstellar dust in R CrB stars is often thought to be due to graphite, because of the high carbon abundance in the stars. Further, the spectra of these stars in the infrared show feature-less smooth continuum (Forrest 1974, Roche and Aitken 1984) which was also thought to be characteristic of graphite. However, the recent comparison of the ultraviolet spectra obtained at maximum and minimum light of R CrB showed an extinction peak in the region of 2400 to 2500A (Holm, Wu & Doherty 1982, Hecht et al. 1984) which was identified as due to amorphous or glassy carbon particles. According to Duley and Williams (1981,83) amorphous carbon is supposed to show spectral features in the 3.3-3.4 μm region. Further many dust emission features are also supposed to appear in the spectral region 3 to 3.5 μm (Aikten 1981). The previous studies in this spectral region in R CrB (Forrest 1974) and in the hotter star V348 Sgr (Allen et al. 1982) showed smooth continuum. V348 Sgr shows spectroscopically many similarities with other WC 11 stars and was grouped with CPD-56°8032, He 2-113 and M4-18 (Webster and Glass 1974). All these three stars show strong dust emission features at 3.3, 8.6 11.25 μm. With a view to search for weaker dust spectral features we obtained the spectrum of R CrB and V348 Sgr with higher resolution than employed before.

The L magnitude of the RCB star, RY Sgr, varies with an amplitud of up to 2.0 mag on a time scale of about 1500 days. The last two deep optical minima have occurred approximately one year after a maximum in L. This behaviour may be characteristic of the star and may allow the time of onset of the next deep minimum to be predicted, in which case it will occur in the second half of 1986.

The absorption line splitting reported by Cottrell and Lambert has been shown to be associated with the semi-regular pulsations. The event has a time scale of about 10 days (0.23 of a period) occuring about the radial velocity reversal at minimum radius. The velocity reversal is more rapid than indicated in an earlier radial velocity analysis by Alexander et al. There is evidence that the phase of the line splitting event is similar to the phase of the onset of the obscurational light declines.

Our idea of the evolutionary state of the hot R CrB-star V348 Sgr is seriously restricted by our ignorance of its effective temperature. A direct determination from photospheric lines is very difficult, owing to contamination by emission lines. Using Johnson photometry, Houziaux (1968) estimated a spectral type of BO or Bl. This result was, however, based on the assumption that V348 Sgr behaves photometrically as a main sequence star. V348 Sgr appears, however, to be an extreme helium star since hydrogen absorption lines are completely absent (Houziaux, 1968). This conclusion has been strengthened by a study of Heber et al. (1984) in which IUE-spectra (low resolution) of V348 Sgr are compared with those of well-known extreme helium stars. From the similarity between these spectra, it was concluded that V348 Sgr must be a helium supergiant with an effective temperature of about 16000 K, though its (dereddened) spectral flux distribution differs in a peculiar way from that of HD 124448 which has about the same temperature. It should, however, be noted that the dereddening was performed by eliminating the λ = 2200 Å dip with Seaton’s law for the interstellar reddening. Obviously, the latter is not applicable when describing the extinction towards V348 Sgr.

In this short note, an attempt has been made to estimate mass and luminosity of the unique object, V348 Sgr, which appears to be a “Rosetta Stone” for our understanding of late stages of stellar evolution, as

1. i) its photosphere is virtually hydrogen-free and carbon-rich as with an extreme helium star,

2. ii) it fades irregularly as does a R CrB-star and

3. iii) it is surrounded by a nebular shell similar to that surrounding Planetary Nebulae.

We know a great deal more about the above-mentioned objects than about V348 Sgr and this knowledge can be used to obtain estimates on mass and luminosity of the latter.

The star HV12842 is one of the 5 R CrB stars listed in the catalogue of variable stars in the LMC (Payne-Goposchkin 1971) and is located 4 deg. to the north of 30 Doradus. At this location it falls in the north-eastern part of one of two standard LMC fields used by the UK 1.2 m Schmidt Telescope. Since 1976 a series of I-plates (normally 90 minute exposures of hypersensitized Kodak IV-N emulsion through a Schott RG 715 filter) has been obtained on both the standard fields (LMC (N) and LMC (S)). This paper describes the behaviour of HV 12842 during the period 1976-1985 as it appears on the 38-I-plates of LMC(N) taken with the UK 1.2 m Schmidt Telescope. Earlier, the UBV magnitude at maximum light are given as V=13.65, B−V=0.51, U−B=−0.11 (Sherwood 1974) and the spectral type as F (Feast 1979).

Hydrogen-poor and helium-rich stars are easy to produce in interacting binaries. Thus they should be found among Population I binaries, in which a large-scale mass transfer has occurred between the components (possibly associated with mass loss from the system). For in such cases, those layers are now on the surface of the “loser” (and, most likely, also on the surface of the “gainer”) that were subject to hydrogen burning and the associated mixing of processed material. Helium overabundance in these objects will be accompanied by an overabundance of nitrogen and underabundance of carbon, as a result of the CNO process. All the Algol-like semidetached binaries should be mild helium stars; so far this has been demonstrated only in β Lyrae, for the He/H ratio is not extreme in such cases. Extreme helium stars require a more complex process, with two stages of mass transfer and/or loss (“case BB”); υ Sagittarii and KS Persei seem to be good examples of this process. The optically invisible components of these two stars seem to have been detected with the IUE. Good model atmospheres do not exist yet, so caution must be exercised in interpreting the UV data.

The hydrogen-deficient star CPD-58°2721 (=LSS1922) has been observed to show radial velocity variations with a range of 140 km s−1. It shows light and colour variations with amplitudes of 0T07 on a timescale of about 9 days. The absorption spectrum is nitrogen-rich and is seen to vary on a short timescale (4 days). CPD-58°2721 therefore appears to be a hydrogen-deficient binary similar to KS Per and v sgr. The photometric variability is attributed to radial pulsation.

A study was carried out for 309 Algol systems to show that most of the secondary components of low mass-ratio systems are hydrogen deficient stars. This hydrogen deficiency is evident from their positions on a Δ log L - Δ log T plot, where Δ is the difference between the observed quantity, log L or log Te, and the value of the same quantity for a star of the same mass on the empirical Main Sequence. The secondary components are shown to occupy the region of mass losing helium dwarfs on this plot. A correlation has also been obtained between the excess of effective temperature and the mass ratio of the system.

Intermediate helium stars are defined by

nHe/nH being the number ratio of He over H. The upper bound which separates the intermediates from the extremes is well-defined (see Sect. 7), whereas the lower bound is rather soft.

The first intermediate helium star discovered was Sigma Ori E (Greenstein and Wallerstein, 1956). Since then, 23 intermediates with V ≤ 1lm have been found (see the list of Walborn, 1983 and also the Annex), mostly through surveys such as that by McConnell et al. (1970) and McConnell (1972). (To this list, the newly discovered object SB 939, Langhans and Heber, 1985, should be added.) It is anticipated that a substantial fraction has as yet escaped detection. The spectral type centres around B2V while nHe/nH is typically of the order of unity.

The intermediate helium stars are exceedingly rare hot analogs of the classical Ap stars, and are the earliest type stars to possess observable global ordered magnetic fields. A recent discovery is the existence of stellar winds which have large scale magnetospheric structure embedded within them. The nature and geometry of the detected fields are summarized, and the modulation of the circumstellar material by the field is illustrated for two examples: the rapid rotator σ Ori E, and the slow rotator HD 184927. The complex variety of stellar wind phenomenology which may be encountered is displayed by a sample of ten helium strong stars. A few of these objects show Hα emission, and thus are the only known magnetic Be stars.

The hydrogen and helium line equivalent widths from stellar atmosphere models for early B stars are presented. The models, which range in helium number fraction from 0.10 to 0.85, result from the non-LTE statistical equilibrium code of Mihalas.

High resolution and signal-to-noise spectra (0.22 A; S/N ≥ 50) of the H-alpha and He I 6678 A lines have been obtained over most of the cycle of the intermediate helium strong star HD 37017 with the Coude spectrograph and CCD camera at KPNO. These spectra are modeled with the non-LTE code of Mihalas to derive properties of the star. Both of the observed lines show small equivalent width variations on the previously known timescale of 0.901 days. The profiles can be simulated by a model with temperature 20,000K, log g=3.4, and helium number fraction 0.25, and which has a helium-rich spot of radius 40° and helium number fraction of 0.60 on the equator. Other possible models are discussed, as well as a model of the weak emission on the wings of H-alpha.

SB 939 was analyzed spectroscopically for the basic atmospheric parameters Teff, log g and helium content. It was shown to be an intermediate helium star (helium abundance = 22% by number) situated unusually far away from star-forming regions.

The peculiar F star HD 60435 exhibits broadband light oscillations of low amplitude with periods between 15 and 4 minutes. Photographic spectra obtained in January/February 1985 using the University of Toronto 0.6 m telescope on Las Campanas, Chile, reveal that the star also undergoes slow spectral variations like those observed in many Ap stars. The data further suggest that Sr II maximum may coincide with maximum amplitude of light oscillations. According to the oblique pulsator model (Kurtz 1982) for such variables, this implies that Sr II is concentrated near at least one of the magnetic poles of HD 60435.

In this review we will discuss the hottest subluminous H-deficient stars, namely those with Teff > 30000 K. In the absence of reliable distance determinations for hot subluminous stars, the best way to discuss their properties and evolutionary status is to find their positions on the log g - log Teff diagram. In the last few years, after extensive computational work, first in Kiel and more recently also in Munich, it has become possible to obtain log g and Teff, together with the surface He abundance, directly by fitting the observed H and He absorption line profiles with theoretical profiles obtained from non-LTE model atmospheres and associated line formation codes. The non-LTE models are plane-parallel, in hydrostatic and radiative equilibrium, and the atmosphere is assumed to consist of H and He only. A recent paper by Groth et al. (1985) gives most of the references on the application of this non-LTE model atmosphere approach to the study of all kinds of hot subluminous stars.