Collective pulsational velocity broadening due to gravity modes as a
physical explanation for macroturbulence in hot massive stars

C. Aerts (1), J. Puls(2), M. Godart(3), M.-A. Dupret(3)

(1)Instituut voor Sterrenkunde, Katholieke Universiteit Leuven,
Celestijnenlaan 200D, B-3001 Leuven, Belgium
(2)Universit"ats-Sternwarte, Scheinerstrasse 1,
D-81679 M"unchen, Germany
(3)Institut d'Astrophysique et G'eophysique,
Universit'e de Li`ege, all'ee du Six Ao^ut 17, B-4000 Li`ege, Belgium

We aimed at finding a physical explanation for the
occurrence of macroturbulence in the atmospheres of hot massive stars, a
phenomenon found in observations since more than a decade but yet
unexplained. We computed time series of line
profiles for evolved massive stars broadened by rotation and by hundreds of
low-amplitude nonradial gravity-mode pulsations which are predicted to be
excited for evolved massive stars. In
general, line profiles based on macrotubulent broadening can mimic those
subject to pulsational broadening. In several cases, though, good fits require
macroturbulent velocities that pass the speed of sound for realistic pulsation
amplitudes. Moreover, we find that the rotation velocity can be seriously
underestimated by using a simple parameter description for macroturbulence
rather than an appropriate pulsational model description to fit the line
profiles. We
conclude that macroturbulence is a likely signature of the collective effect
of pulsations. We provide line diagnostics and their typical values to decide
whether or not pulsational broadening is present in observed line profiles, as
well as a procedure to avoid an inaccurate estimation of the rotation

Reference: Accepted for publication in Astronomy & Astrophysics
Status: Manuscript has been accepted