We report the recovery of a spectroscopic event in h Carinae in 1997/1998 after a prediction by Damineli in 1996. A true periodicity with days (0.2% uncertainty) is obtained. The line intensities and the P = 2020 ‫ע‬ 5 radial velocity curve display a phase-locked behavior, implying that the energy and dynamics of the event repeat from cycle to cycle. This rules out S Doradus oscillation or multiple shell ejection by an unstable star as the explanation of the spectroscopic events. A colliding-wind binary scenario is supported by our spectroscopic data and by X-ray observations. Although deviations from a simple case exist around periastron, intensive monitoring during the next event (mid-2003) will be crucial to our understanding of the system.

Abstract.We have extensively monitored the Luminous Blue Variable AG Car (HD 94910) spectroscopically. Our data cover the years 1989 to 1999. In this period, the star underwent almost a full S Dor cycle from visual minimum to maximum and back. Over several seasons, up to four months of almost daily spectra are available. Our data cover most of the visual spectral range with a high spectral resolution (λ/∆λ ≈ 20 000). This allows us to investigate the variability in many lines on time scales from days to years. The strongest variability occurs on a time scale of years. Qualitatively, the variations can be understood as changes of the effective temperature and radius, which are in phase with the optical light curve. Quantitatively, there are several interesting deviations from this behaviour, however. The Balmer lines show P Cygni profiles and have their maximum strength (both in equivalent width and line flux) after the peak of the optical light curve, at the descending branch of the light curve. The line-width during maximum phase is smaller than during minimum, but it has a local maximum close to the peak of the visual light curve. We derive mass-loss rates over the cycle from the Hα line and find the highest mass loss rates (logṀ /(M yr −1 ) ≈ −3.8, about a factor of five higher than in the minimum, where we find logṀ/(M yr −1 ) ≈ −4.5) after the visual maximum. Line-splitting is very commonly observed, especially on the rise to maximum and on the descending branch from maximum. The components are very long-lived (years) and are probably unrelated to similar-looking line-splitting events in normal supergiants. Small apparent accelerations of the components are observed. The change in radial velocity could be due to successive narrowing of the components, with the absorption disappearing at small expansion velocities first. In general, the linesplitting is more likely the result of missing absorption at intermediate velocities than of excess absorption at the velocities of the components. The Hei lines and other lines which form deep in the atmosphere show the most peculiar variations. The Hei lines show a central absorption with variable blue-and red-shifted emission components. Due to the variations of the emission components, the Hei lines can change their line profile from a normal P Cyg profile to an inverse P Cyg-profile or double-peak emission. In addition, very broad (±1500 km s −1 ) emission wings are seen at the strongest Hei lines of AG Car. At some phases, a blue-shifted absorption is also present. The central absorption of the Hei lines is blue-shifted before and red-shifted after maximum. Possibly, we directly see the expansion and contraction of the photosphere. If this explanation is correct, the velocity of the continuum-forming layer is not dominated by expansion but is only slightly oscillating around the systemic velocity.

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Abstract. We present chemical abundances for four main sequence B stars in the young cluster NGC 2004 in the Large Magellanic Cloud (LMC). Apart from H ii regions, unevolved OB-type stars are currently the only accessible source of present-day CNO abundances for the MCs not altered by stellar evolution. Using UVES on the VLT, we obtained spectra of sufficient resolution (R = 20 000) and signal-to-noise (S/N ≥ 100) to derive abundances for a variety of elements (He, C, N, O, Mg and Si) with NLTE line formation. This study doubles the number of main sequence B stars in the LMC with detailed chemical abundances. More importantly and in contrast to previous studies, we find no CNO abundance anomalies brought on by e.g. binary interaction or rotational mixing. Thus, this is the first time that abundances from H ii regions in the LMC can sensibly be cross-checked against those from B stars by excluding evolutionary effects. We confirm the H ii-region CNO abundances to within the errors, in particular the extraordinarily low nitrogen abundance of ε(N) 7.0. Taken at face value, the nebular carbon abundance is 0.16 dex below the B-star value which could be interpreted in terms of interstellar dust depletion. Oxygen abundances from the two sources agree to within 0.03 dex. In comparison with the Galactic thin disk at MC metallicities, the Magellanic Clouds are clearly nitrogen-poor environments.

Abstract.After the description and time series analysis of the variability of the circumstellar and stellar lines, respectively, in Papers I and II of this series, this paper sets out to model the stellar variability in terms of multimode nonradial pulsation (nrp), but also adds another 109 echelle spectra to the database, obtained in 1999. While the near-circumstellar emission has faded further, the six periods and the associated line profile variabilities (lpv) have remained unchanged. For the modeling, P1 of the periods P1-P4 close to 0.5 day, and P5 of the two periods P5 and P6 near 0.28 day were selected, because they have the largest amplitude in their respective groups, which are characterized by their own distinct phase-propagation pattern. Permissable ranges of mass, radius, effective temperature, projected equatorial rotation velocity, and inclination angle were derived from calibrations and observations available in the literature. A total of 648 different combinations of these parameters were used to compute a number of trial series of line profiles for comparison with the observations. Next to reproducing the observed variability, the primary constraint on all models was that the two finally adopted solutions for P1 and P5 had to be based on only one common set of values of these quantities. This was, in fact, accomplished. Townsend's (1997b) code Bruce was deployed to model the pulsational perturbations of the rotationally distorted stellar surface. With the help of Kylie, from the same author, these perturbations were converted into observable quantities. The local flux and the atmosphere structure were obtained from a grid of Atlas9 models with solar metallicity, while the formation of 5967 spectral lines was calculated with the LTE code of Baschek et al. (1966). An initial coarse grid of models using all these ingredients was computed for all 12 nrp modes with ≤ 3 and m = 0. Comparison with the observed variability of C ii 4267, which is the best compromise between contamination by circumstellar emission and significance of the variability, yielded ( = 2, m = +2) for P1 (and, by implication, P2-P4) and ( = 3, m = +3) for P5 (and P6) as the best matching nrp modes. At 9 M / 3.4 R and 440 km s −1 , respectively, the mass-to-radius ratio and the equatorial velocity are on the high side, but not in fundamental conflict with established knowledge. The photometric variations of all six modes combine at most to a maximal peak-to-peak amplitude of 0.015 mag, consistent with the non-detection of any of the spectroscopic periods by photometry. Without inclusion of additional physical processes, present-day linear nrp models are fundamentally unable to explain major red-blue asymmetries in the power distribution, which however seem to be limited to only some lines and the modes with the highest amplitudes. Nevertheless, the model reproduces very well a wide range of observed details. Most notable among them are: (i) Although all modeling was done on the residuals from the mean profiles only, the mean spect...