The absorption‐line spectra of early B‐type supergiants show significant broadening that implies that an additional broadening mechanism (characterized here as ‘macroturbulence’) is present in addition to rotational broadening. Using high‐resolution spectra with signal‐to‐noise ratios of typically 500, we have attempted to quantify the relative contributions of rotation and macroturbulence, but even with data of this quality significant problems were encountered. However, for all our targets, a model where macroturbulence dominates and rotation is negligible is acceptable; the reverse scenario leads to poor agreement between theory and observation. Additionally, there is marginal evidence for the degree of broadening increasing with line strength, possibly a result of the stronger lines being formed higher in the atmosphere. Acceptable values of the projected rotational velocity are normally less than or equal to 50 km s−1, which may also be a typical upper limit for the rotational velocity. Our best estimates for the projected rotational velocity are typically 10–20 km s−1 and hence compatible with this limit. These values are compared with those predicted by single star evolutionary models, which are initially rapidly rotating. It is concluded that either these models underestimate the rate of rotational breaking or some of the targets may be evolving through a blue loop or are binaries.

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Abstract. High-resolution observations of five OB-type main-sequence stars in the Large Magellanic Cloud (LMC) have been obtained with the UCLéchelle spectrograph on the 3.9-m Anglo-Australian Telescope. These spectra have been analysed using LTE model-atmosphere techniques, to derive stellar atmospheric parameters and chemical compositions. As these stars are located within the hydrogen burning main-sequence band, their surface abundances should reflect those of the present-day interstellar medium. Detailed line-by-line differential analyses have been undertaken relative to Galactic comparison stars. We conclude that there exists a general metal deficiency of −0.31 ± 0.04 dex within the LMC, and find no significant abundance variations between cluster and field stars. There is also tentative evidence to suggest a lower oxygen to iron abundance ratio, and an over-deficiency of magnesium relative to the other α-elements. These are discussed in terms of previous abundance analyses and models of discontinuous (or bursting) star formation within the LMC. Finally, there is some evidence to suggest a greater chemical enrichment of material within the H  region LH 104.

Abstract. High-resolution spectroscopic VLT/UVES observations are presented for the B-type main-sequence star, AV 304, in the Small Magellanic Cloud (SMC). These spectra have been analysed using LTE model-atmosphere techniques, to derive stellar atmospheric parameters and chemical compositions. As AV 304 is located within the hydrogen burning main-sequence band, its chemical composition should reflect that of the SMC interstellar medium (ISM). A detailed line-by-line differential analysis has been undertaken relative to a Galactic comparison star. A general metal deficiency for the α-process elements O, Si & S of −0.43 ± 0.05 dex is found for AV 304, with iron having a similar underabundance. Oxygen may be relatively overabundant by ∼0.1 dex and carbon and aluminium underabundant by ∼0.2 dex. A large nitrogen underabundance (of −1.2 dex relative to hydrogen and −0.7 dex relative to iron) is found. This is interpreted in terms of the CNO bi-cycle having been suppressed in the SMC. Furthermore, the large nitrogen deficiency is in excellent agreement with that found for SMC H  regions. Indeed, this represents a first for stellar astrophysics -confirming the low base-line nitrogen composition of the SMC ISM (viz. 12+log(N/H) ∼ 6.66 ± 0.10 dex).

Abstract. High spectral resolution and signal-to-noise observations of the absorption and emission line spectra in two postasymptotic-giant-branch (PAGB) stellar candidates, LSIV −12 111 and HD 314617 are discussed. The absorption line spectra have been analysed using non-LTE model atmosphere techniques to determine stellar atmospheric parameters and chemical compositions, both in absolute terms and relative to a standard star, HD 13841. The atmospheric parameters differ from previous estimates based on LTE model atmospheres, probably due to non-LTE effects. In turn these imply stellar masses that are generally larger than have been previously estimated. Both PAGB candidates have relative uniform underabundances of metals with mean values of −0.35 dex for LSIV −12 111 and −0.50 dex for HD 314617. Furthermore, their abundance patterns are remarkably similar to that observed for optically bright, F-type PAGBs. From the emission spectra, the plasma parameters and angular size of the circumstellar material are constrained, and these are consistent with previous estimates and with a PAGB evolutionary stage.