Fundamental parameters and the carbon , nitrogen and oxygen abundances are determined for 22 B-type stars with distances d \leq 600  pc and slow rotation ( v \sin i \leq 66  km s ^ { -1 } ) .
The stars are selected according to their effective temperatures T _ { eff } and surface gravities \log g , namely : T _ { eff } is between 15300 and 24100Â K and \log g is mostly greater than 3.75 ; therefore , stars with medium masses of 5-11 M _ { \odot } are selected .
Theory predicts for the stars with such parameters that the C , N and O abundances in their atmospheres should correspond to their initial values .
Non-LTE analysis of CÂ II , NÂ II and OÂ II lines is implemented .
The following mean C , N and O abundances are obtained : \log \epsilon ( C ) Â =Â 8.31 \pm 0.13 , \log \epsilon ( N ) Â =Â 7.80 \pm 0.12 and \log \epsilon ( O ) Â =Â 8.73 \pm 0.13 .
These values are in very good agreement with recent data on the C , N and O abundances for nearby B stars from other authors ; it is important that different techniques are applied by us and other authors .
When excluding for the stars HRÂ 1810 and HRÂ 2938 , which can be mixed , we obtain the following mean abundances for the remaining 20 stars : \log \epsilon ( C ) Â =Â 8.33 \pm 0.11 , \log \epsilon ( N ) Â =Â 7.78 \pm 0.09 and \log \epsilon ( O ) Â =Â 8.72 \pm 0.12 ; these values are in excellent agreement with a present-day Cosmic Abundance Standard ( CAS ) of Nieva & Przybilla .

The derived mean N and O abundances in unevolved B stars are very close to the solar photospheric abundances , as well as to the protosolar ones .
However , the mean C abundance is somewhat lower than the solar one ; this small but stable carbon deficiency is confirmed by other authors .
One may suggest two possibilities to explain the observed C deficiency .
First , current non-LTE computations of CÂ II lines are still partially inadequate .
In this case the C deficiency is invalid , so one may conclude that the Sun and the local unevolved B stars have the same metallicity .
This would mean that during the Sun ’ s life ( i.e. , for the past 4.5 \cdot 10 ^ { 9 } yr ) the metallicity of the solar neighbourhood has not markedly changed ; so , an intensive enrichment of the solar neighbourhood by metals occurred before the Sun ’ s birth .
Second , the C deficiency in the local B stars is valid ; it is supposed that the Sun can migrate during its life from inner parts of the Galactic disk where it has born , so its observed chemical composition can differ from the composition of young stars in its present neighbourhood .