Non-local thermodynamic equilibrium analysis of He I lines in spectra of 102 B stars is implemented in order to derive the helium abundance He/H, the microturbulent parameter V t and the projected rotation velocity v sin i. A simultaneous determination of He/H and V t for the stars is effected by analysing equivalent widths of the 4471-and 4922-Å lines primarily as indicators of He/H and the 4713-, 5016-, 5876-and 6678-Å lines primarily as indicators of V t . The rotation velocities v sin i are found from profiles of the same lines. It is shown that, when V t > 7 km s −1 , the V t (He I) values determined from He I lines are systematically overestimated as compared with the V t (O II, N II) values derived from O II and N II lines. This discrepancy is especially appreciable for hot evolved B giants with V t (He I) = 16-23 km s −1 and may indicate a failure of classical model atmospheres to represent the strong He I lines for these stars.Two programme stars, HR 1512 and 7651, are found to be helium-weak stars. The remaining 100 stars are divided into three groups according to their masses M. The microturbulent parameter V t (He I) is low for all stars of group A (M = 4.1-6.9 M ) and for all stars with the relative ages t/t MS < 0.8 of group B (M = 7.0-11.2 M ). Their V t (He I) values are within the 0 to 5 km s −1 range, as a rule; the mean value is V t = 1.7 km s −1 . Only evolved giants of group B, which are close to the termination of the main-sequence (MS) evolutionary phase (t/t MS > 0.8), show V t (He I) up to 11 km s −1 . The helium abundance He/H is correlated with the relative age t/t MS in both groups; the averaged He/H enhancement during the MS phase is 26 per cent. For group C, containing the most massive stars (M = 12.4-18.8 M ), the V t (He I) values display a correlation with t/t MS , varying from 4 to 23 km s −1 . The He/H determination for hot evolved B giants of the group with V t (He I) > 15 km s −1 depends on a choice between the V t (He I) and V t (O II, N II) scales. The mean He/H enrichment by 67 per cent during the MS phase is found, if the abundances He/H are based on the V t (O II, N II) scale; however, two evolved giants with especially high v sin i, HR 7446 and 7993, show the He/H enhancement by about a factor of 2.5. When using the same V t scale, we found a trend of He/H with projected rotational velocities v sin i; a large dispersion for v sin i > 150 km s −1 can result from differences in masses M.A comparison with the stellar model computations with rotationally induced mixing shows that the observed helium enrichment during the MS phase can be explained by rotation with initial velocities 250-400 km s −1 . The He/H distribution on M and v sin i based on the V t (O II, N II) scale seems to be in better agreement with the theory than one based on the V t (He I) scale. The mean value He/H = 0.10 derived for stars in the zero age main sequence (ZAMS) vicinity can be adopted as the typical initial helium abundance for early B stars in the solar neighbourhood. Non-LTE computations of He ...

The following parameters are determined for 63 Galactic supergiants in the solar neighbourhood: effective temperature T eff ; surface gravity log g; iron abundance log (Fe); microturbulent parameter V t ; mass M/M ; age t and distance d. A significant improvement in the accuracy of the determination of log g, and all parameters dependent on it, is obtained through application of van Leeuwen rereduction of the Hipparcos parallaxes. The typical error in the log g values is now ±0.06 dex for supergiants with distances d < 300 pc and ±0.12 dex for supergiants with d between 300 and 700 pc; the mean error in T eff for these stars is ±120 K. For supergiants with d > 700 pc, parallaxes are uncertain or unmeasurable, so typical errors in their log g values are 0.2-0.3 dex.A new T eff scale for A5-G5 stars of luminosity classes Ib-II is presented. Spectral subtypes and luminosity classes of several stars are corrected. Combining the T eff and log g with evolutionary tracks, stellar masses and ages are determined; a majority of the sample has masses between 4 and 15 M and, hence, their progenitors were early to middle B-type main-sequence stars.Using Fe II lines, which are insensitive to departures from local thermodynamic equilibrium, the microturbulent parameter V t and the iron abundance log (Fe) are determined from highresolution spectra. The parameter V t is correlated with gravity: V t increases with decreasing log g. The mean iron abundance for the 48 supergiants with distances d < 700 pc is log (Fe) = 7.48 ± 0.09, a value close to the solar value of 7.45 ± 0.05, and thus the local supergiants and the Sun have the same metallicity.

No abstract

Using new accurate fundamental parameters of 30 Galactic A and F supergiants, namely their effective temperatures T eff and surface gravities log g, we implemented a non-LTE analysis of the nitrogen abundance in their atmospheres. It is shown that the non-LTE corrections to the N abundances increase with T eff . The nitrogen overabundance as a general feature of this type of stars is confirmed. A majority of the stars have a nitrogen excess [N/Fe] between 0.2 and 0.9 dex with the maximum position of the star's distribution on [N/Fe] between 0.4 and 0.7 dex. The N excesses are discussed in light of predictions for B-type main sequence (MS) stars with rotationally induced mixing and for their next evolutionary phase, i.e. A-and F-type supergiants that have experienced the first dredge-up. Rotationally induced mixing in the MS progenitors of the supergiants may be a significant cause of the nitrogen excesses. When comparing our results with predictions of the theory developed for stars with the mixing, we find that the bulk of the supergiants (28 of 30) show the N enrichment that can be expected (i) either after the MS phase for stars with the initial rotational velocities v 0 = 200-400 km s −1 (ii) or after the first dredge-up for stars with v 0 = 50-400 km s −1 . The latter possibility is preferred on account of the longer lifetime for stars on red-blue loops following the first dredge-up. Two supergiants without a discernible N enrichment, namely HR 825 and HR 7876, may be post-MS objects with the relatively low initial rotational velocity of about 100 km s −1 . The suggested range for v 0 is approximately consistent with inferences from the observed projected rotational velocities of B-type MS stars, progenitors of A and F supergiants.

Effective temperatures Teff, surface gravities log g and interstellar extinctions AV are found for 107 B stars. Distances d of the stars, which are based on the derived Teff, log g and AV values, show good agreement with those obtained from the Hipparcos parallaxes. Comparing the Teff and log g values with evolutionary computations, we infer masses, radii, luminosities, ages and relative ages of the stars. Empirical relations between the Teff and log g parameters, on the one hand, and the photometric indices Q, [c1] and β, on the other hand, are constructed; these relations give a fast method for the Teff and log g estimation of early and medium B stars. Inclusion of the infrared J, H and K colours into the Teff, log g and AV determination shows that (i) the Teff and log g parameters are altered only slightly; (ii) the AV value is rather sensitive to these colours, so an accuracy better than 0.05 mag in the JHK data is necessary for precise AV evaluation.