We investigate the effects of radiation pressure on the atmospheres of A, F and G-supergiants by calculating hydrodynamical model atmospheres for stars with 5500 ≤ Teff ≤ 9500 K. In the subsonic part of the wind, the radiation pressure by continuum and lines from Kurucz (1992) is taken into account. In the supersonic part of the wind, the radiation pressure is expressed in terms of the force mu...

Stellar evolution calculations predict the flux-weighted gravity g/T 4 eff and absolute bolometric magnitude of blue supergiants to be strongly correlated. We use medium resolution multi-object spectroscopy of late B and early A supergiants in two spiral galaxies, NGC 300 and NGC 3621, to demonstrate the existence of such a relationship, which proves to be surprisingly tight. An analysis of hig...

NGC 330 is the brightest SMC young cluster and contains many bright supergiants. This cluster has aroused special interest, since the earlier abundance determinations indicated an abundance lower by a factor ∼5 than in the SMC field young population. Taking advantage of our previous high resolution analysis of a sample of type K supergiants in the SMC field (Paper I and II), we analyse 6 cool s...

We compare our latest single and binary stellar model results from the Cambridge STARS code to several sets of observations. We examine four stellar population ratios, the number of blue to red supergiants, the number of Wolf-Rayet stars to O supergiants, the number of red supergiants to Wolf-Rayet stars and the relative number of Wolf-Rayet subtypes, WC to WN stars. These four ratios provide a...

We present a classification of 267 new variable Btype stars discovered by Hipparcos. We have used two different classification schemes and they both result in only a few new β Cephei stars, a huge number of new slowly pulsating B stars, quite some supergiants with αCyg-type variations and variable CP stars, and further some new periodic Be stars and eclipsing binaries. Our results clearly point...

We present a study of the photometric variability of spectroscopically confirmed supergiants in NGC 300, comprising 28 epochs extending over a period of five months. We find 15 clearly photometrically variable blue supergiants in a sample of nearly 70 such stars, showing maximum light amplitudes ranging from Based on observations obtained with the 2.2m ESO/MPI telescope at the European Southern...

We present two classes of stars with yet unknown evolutionary phase: the B[e] supergiants and the so-called unclassified B[e] stars. While the B[e] supergiants are luminous post-main sequence stars with high mass progenitors, not much is known of the unclassified stars. We discuss how it might be possible to determine their evolutionary phases in the area of new large telescopes.

FifteenO andB supergiants have been observedwith the Very Large Array (VLA) at 4.85, 8.45, and 14.95 GHz in order to make a detailed comparative study of the mass loss rates evaluated from Hα and radio continuum observations and reveal and quantify possible departures from standardwind conditions. We detected 12 sources, 7 of which for the first time, thus increasing by 30% the total number of ...