Jacques Chauville

NEW LAMBDA BOOTIS STARS WITH A SHELL

We publish here the second part of our spectroscopic survey at high dispersion of some known and suspected λ Bootis stars with a view to detecting circumstellar shell features. Eight stars of our sample exhibit such features. These stars are fast rotators, a result which is in line with Hohlweger and Rentzsch-Holms study (1995). The analysis of the photometric data has allowed us to confirm the exclusion of a few stars misclassified from the λ Bootis group.

A 10-h period revealed in optical spectra of the highly variable WN8 Wolf-Rayet star WR 123

Aims. What is the origin of the large-amplitude variability in Wolf-Rayet WN8 stars in general and WR123 in particular? A dedicated spectroscopic campaign targets the ten-hour period previously found in the high-precision photometric data obtained by the MOST satellite. Methods. In June-August 2003 we obtained a series of high signal-to-noise, mid-resolution spectra from several sites in the {\lambda}{\lambda} 4000 - 6940 A^{\circ} domain. We also followed the star with occasional broadband (Johnson V) photometry. The acquired spectroscopy allowed a detailed study of spectral variability on timescales from \sim 5 minutes to months. Results. We find that all observed spectral lines of a given chemical element tend to show similar variations and that there is a good correlation between the lines of different elements, without any significant time delays, save the strong absorption components of the Hei lines, which tend to vary differently from the emission parts. We find a single sustained periodicity, P \sim 9.8 h, which is likely related to the relatively stable pulsations found in MOST photometry obtained one year later. In addition, seemingly stochastic, large-amplitude variations are also seen in all spectral lines on timescales of several hours to several days.

EVOLUTION OF THE CIRCUMSTELLAR SHELL OF PLEIONE (1981-94)

Three spectra of Pleione (1981, 1987-88, 1994), obtained in the blue wavelength range, show strong long-term changes which indicate that the surrounding shell, first rather cool and close to the central star, then expands gradually in the equatorial plane of the star and towards the poles. From 1981 to 1987-88, the spectrum of Pleione is that of the central star, with a cool shell which globally mimics a late-type star. The year 1994 is marked by a pure and stronger Be spectrum, with no shell line.

Long-Term Spectroscopic and Polarimetric Variations of the Be Star к Dra

The bright Be star к Dra (HD 109387, B5 III, v.sini=249 km/s) is one of the rare mid B type stars which have presented FeII emission lines during strong emission phases. Spectroscopic variations were previously reported by many authors over different time scales: years, days and hours. Juza et al. (1991) proposed that к Dra was the primary component of a binary system with Porb. = 61.55 days. Short-term and long-term variations in the linear optical polarization were also reported by Arsenijevic et al. (1986). We have tried, with our extensive joint material, to search for correlation between long-term spectroscopic and polarimetric variations with the aim of obtaining information on the behaviour of the circumstellar envelope.