EVOLUTIONARY VARIATIONS OF NITROGEN AND H ELIUM ABUNDANCES IN EARLY B-TYPE MAIN-SEQUENCE STARS - AN ANALYSIS OF NEW DATA

The latest data on nitrogen, carbon and helium abundances in atmospher es of early B-type main-sequence (MS) stars obtained by Gies and Lambe rt and by Kilian are analyzed The results of these authors are shown l o confirm our correlation between the nitrogen abundance and the age o f stars, if some essential circumstances are taken into account (in pa rticular, if a rather strict selection of stars is made). The total in crease of nitrogen abundance during the MS phase in about 0,4 dex for a star with a mass M = 10-11 M. and almost 0,6 dex for a star with M = 12,5 M. It is shown that the helium abundance He/H increases during t he MS phase by the value 0,05, which completely corresponds to our pre vious evaluation for B-stars with masses M = 8-15 M.. Carbon shows ste ady underabundance (about 0,4 dex on the average), which is not depend ent on the age however, at the same time the condition of constancy of the total abundance C + N is not fulfill for B-type MS stars and the following stage of yellow supergiants.