1995A&A...301..155B

This paper presents new statistical studies based on a sample of 29 Herbig Ae/Be stars spectra, mostly observed with the MUSICOS echelle spectrograph at the Telescope Bernard Lyot at the Pic du Midi Observatory. The high S/N spectra cover the visible domain with a resolution of R=38000. Two major problems are investigated in detail. After a precise redetermination of the v.sin(i) of our objects, we study in detail the angular momentum evolution of these PMS stars of intermediate mass, by comparing their v.sin(i) distribution with that of A- and B-type stars in young open clusters. Our data show that, if the stars rotate as solid bodies, low mass Herbig stars (M≤2.6M☉) lose a large fraction of their angular momentum during their PMS evolution, which could be accounted for by stellar winds with mass loss rates of the order of 10^–8M☉/yr; intermediate mass Herbig stars (between 2.6 and 4 M☉) do not lose a significant fraction of their angular momentum; finally, higher mass Herbig stars (M ≥ 4M☉) seem to gain large amounts of angular momentum. Alternatively, the observed v.sin(i) distributions for Herbig stars and in young open clusters are roughly consistent with a conservation of total angular momentum at all masses if the internal rotation rate varies across the star, e.g. if {OMEGA}(r) goes as r^–2 (constant specific angular momentum). As a second major point, we analyze activity and wind tracers like CaII IR triplet, HeI 5876A and Hα lines, by estimating the excess of the observed line luminosities and surface fluxes with respect to standard photospheric models. We find that the ratio of the excess-line luminosities to the total stellar luminosities presents a maximum at spectral type A0, while the excess-line fluxes increase monotonically with effective temperature. We show that this behavior tends to contradict the suggestion that the origin of activity and winds in these stars may be linked to a boundary layer between the star and an accretion disk. No correlation was found between the various tracers and the projected rotation velocity.