标题：Critical study of the distribution of rotational velocities of Be stars - I. Deconvolution methods, effects due to gravity darkening, macroturbulence, and binarity
其他标题：I. Deconvolution methods, effects due to gravity darkening,
macroturbulence, and binarity⋆
摘要：Context. Among intermediate-mass and massive stars, Be stars are the
fastest rotators in the main sequence (MS) and, as such, these stars are a cornerstone to
validate models of structure and evolution of rotating stars. Several phenomena, however,
induce under- or overestimations either of their apparent Vsini, or
true velocity V.
Aims. In the present contribution we aim at obtaining distributions of
true rotational velocities corrected for systematic effects induced by the rapid rotation
itself, macroturbulent velocities, and binarity.
Methods. We study a set of 233 Be stars by assuming they have
inclination angles distributed at random. We critically discuss the methods of Cranmer and
Lucy-Richardson, which enable us to transform a distribution of projected velocities into
another distribution of true rotational velocities, where the gravitational darkening
effect on the Vsini parameter is considered in
different ways. We conclude that iterative algorithm by Lucy-Richardson responds at best
to the purposes of the present work, but it requires a thorough determination of the
stellar fundamental parameters.
Results. We conclude that once the mode of ratios of the true velocities
of Be stars attains the value V/Vc ≃
0.77 in the main-sequence (MS) evolutionary phase, it remains unchanged
up to the end of the MS lifespan. The statistical corrections found on the distribution of
ratios V/Vc
for overestimations of Vsini, due to macroturbulent
motions and binarity, produce a shift of this distribution toward lower values of
V/Vc
when Be stars in all MS evolutionary stages are considered together. The mode of the final
distribution obtained is at V/Vc ≃
0.65. This distribution has a nearly symmetric distribution and shows
that the Be phenomenon is characterized by a wide range of true velocity ratios
0.3 ≲
V/Vc ≲
0.95. It thus suggests that the probability that Be stars are critical
rotators is extremely low.
Conclusions. The corrections attempted in the present work represent an
initial step to infer indications about the nature of the Be-star surface rotation that
will be studied in the second paper of this series.
