6 Summary and conclusions

The determination of projected rotational velocities is sullied with several effects which affect the measurement. The blend of spectral lines tends to produce an overestimated value of , whereas the lowering of the measured continuum level due to high rotation tends to lower the derived . The solution lies in a good choice of candidate lines to measure the rotational velocity. The use of the additional spectral range 4500-4600 Å, compared to the observed domain in Paper I, allows for the choice of reliable lines that can be measured even in case of high rotational broadening and reliable anchors of the continuum, for the considered range of spectral types. The is derived from the first zero of Fourier transform of line profiles chosen among 23 candidate lines according to the spectral type and the rotational blending. It gives resulting for 249 stars, with a precision of about 5%.

The systematic shift with standard stars from SCBWP, already detected in Paper I, is confirmed in this work. SCBWP's values are underestimated, smaller by a factor of 0.8 on average, according to common stars in the northern sample. When joining both intersections of northern and southern samples with standard stars from SCBWP, the relation between the two scales is about $\ensuremath{v\sin i} =1.03~{\ensuremath{v\sin i} }_{\rm SCBWP}+7.7$, using these 52 stars in common. This is approximately our findings concerning the catalogue made by Abt & Morrell (1995). They derive their from the calibration built by SCBWP, and reproduce the systematic shift.

In the aim of gathering a large and homogeneous sample of projected rotational velocities for A-type stars, the new data, from the present paper and from Paper I, are merged with the catalogue of Abt & Morrell. First, the from the latter catalogue are statistically corrected from the above mentioned systematic shift. The final sample contains for 2151 B8- to F2-type stars.

The continuation of this work will consist in determining and analyzing the distributions of rotational velocities (equatorial and angular) for different sub-groups of spectral type, starting from the .

Acknowledgements

We insist on warmly thanking Dr. M. Ramella for having provided the programme of determination of the rotational velocities. We are also very grateful to Dr. R. Faraggiana for her precious advice about the analysis of the spectra. We would like to acknowledge Dr. F. Sabatié for his careful reading of the manuscript.