Issue |
A&A
Volume 368, Number 3, March IV 2001
|
|
---|---|---|
Page(s) | 912 - 931 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361:20000577 | |
Published online | 15 March 2001 |
Statistical analysis of intrinsic polarization, IR excess and projected rotational velocity distributions of classical Be stars*
1
Central Astronomical Observatory of the Russian Academy of Sciences at Pulkovo, 196140 Saint-Petersburg, Russia
2
Isaac Newton Institute of Chile, St.-Petersburg Branch, Chile
Received:
9
December
1999
Accepted:
22
December
2000
We present the results of statistical analyses of a sample
of 627 Be stars. The parameters of intrinsic polarization
, projected rotational velocity
,
and near IR excesses have been investigated.
The values of
have been estimated for
a much larger and more representative sample of Be stars
(≈490 objects) than previously.
We have confirmed that most Be stars of early spectral
type have statistically larger values of polarization and IR
excesses in comparison with the late spectral type stars.
It is found that the distributions of
diverge
considerably for the different spectral subgroups. In contrast to
late spectral types (B5-B9.5), the distribution of
for B0-B2 stars does not peak at the value
% .
Statistically significant differences in the mean projected rotational
velocities (
) are found for different spectral
subgroups of Be stars in the sense that late spectral type stars
(V luminosity class) generally rotate faster than early types,
in agreement with previously published results.
This behaviour is, however, not obvious for the III-IV luminosity
class stars. Nevertheless, the calculated values of the ratio
of the true rotational velocity, vt, to the critical
velocity for break-up, vc, is larger for late spectral
type stars of all luminosity classes. Thus, late spectral type stars
appear to rotate closer to their break-up rotational velocity.
The distribution of near IR excesses for early spectral subgroups
is bi-modal, the position of the second peak displaying
a maximum value
for O-B1.5 stars, decreasing to
for intermediate spectral types (B3-B5).
It is shown that bi-modality disappears for late spectral types (B6-B9.5).
No correlations were found between
and near IR excesses
and between
and
for the different subgroups of
Be stars. In contrast to near IR excesses, a relation between
and far IR excesses at 12 μm is clearly seen.
A clear relation between
and
(as well as between
and
) is found by
the fact that plots of these parameters are bounded by a "triangular"
distribution of
:
, with a decrease of
towards very small and very large
(and
)
values. The latter behaviour can be understood in the context of a larger
oblateness of circumstellar disks for the stars with a rapid rotation.
From the analysis of correlations between different observational
parameters we conclude that circumstellar envelopes for the majority of
Be stars are optically thin disks with the range of the half-opening angle
of
.
Key words: classical Be stars: polarization / projected rotational velocities / near IR excesses / far IR excesses
© ESO, 2001
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