Stellar and circumstellar activity of the Be star
CMa
- I. Line and continuum emission in 1996 - 2002
S. Stefl1,
D. Baade2,
Th. Rivinius2,3,
S. Otero4,5,
O. Stahl3,
A. Budovicova1,
A. Kaufer6, and
M. Maintz3
1
Astronomical Institute, Academy of Sciences,
CZ-251 65 Ondrejov, Czech Republic
2
European Southern Observatory, Karl-Schwarzschild-Str. 2, D-85748
Garching bei München, Germany
3
Landessternwarte Königstuhl, D-69117 Heidelberg, Germany
4
Liga Iberoamericana de Astronomia, Buenos Aires, Argentina
5
Centro de Estudios Astronomicos, Mar Del Plata, Argentina
6
European Southern Observatory, Casilla 19001, Santiago 19, Chile
Echelle spectroscopy and mostly unaided-eye photometry of
the southern Be star
CMa were obtained in the period
1996 - 2003. The monitoring is bracketed by two brightenings by
0.4 - 0.5 mag. The results of a literature search
suggest that such phases occur about once a decade and have various
commonalities. Along with these photometric events goes
enhanced line emission. This is due to an increased total mass of the
disk as well as to a change in its density profile. The models by
Poeckert & Marlborough (1978, 1979) imply that the
enhanced continuum flux originates from the inner disk. Higher-order
Balmer line emission is correlated with brightness. The increase in
H is retarded by some months,
possibly indicating a time delay
in filling up and ionizing the outer disk. In the (U-B) vs.
(B-V) colour diagram and the D54 vs. D34 Balmer
decrement diagram the path from the ground to the bright state is
distinct from the return path. This could result from the bulk of the
disk matter being in the outer (inner) disk during the photometric
ground (high) state, while the two transitions between the two states
are both due to changes progressing radially outward. Some
Cen-like outbursts (Rivinius
et al. 1998) seem to occur in
all phases. It is conceivable that the build-up of the inner disk is
caused by more frequent or more effective outbursts. During the
photometric bright state various other phenomena gain in prominence
and suggest this to be a phase of increased activity. Of particular
interest, but possibly only apparently related to this phase, are
absorption components at redshifts well beyond the range covered by
the combination of rotation and nonradial pulsation.
CMa
CMa were obtained in the period
1996 - 2003. The monitoring is bracketed by two brightenings by
0.4 - 0.5 mag. The results of a literature search
suggest that such phases occur about once a decade and have various
commonalities. Along with these photometric events goes
enhanced line emission. This is due to an increased total mass of the
disk as well as to a change in its density profile. The models by
Poeckert & Marlborough (1978, 1979) imply that the
enhanced continuum flux originates from the inner disk. Higher-order
Balmer line emission is correlated with brightness. The increase in
H
is retarded by some months,
possibly indicating a time delay
in filling up and ionizing the outer disk. In the (U-B) vs.
(B-V) colour diagram and the D54 vs. D34 Balmer
decrement diagram the path from the ground to the bright state is
distinct from the return path. This could result from the bulk of the
disk matter being in the outer (inner) disk during the photometric
ground (high) state, while the two transitions between the two states
are both due to changes progressing radially outward. Some
Cen-like outbursts (Rivinius
et al. 1998) seem to occur in
all phases. It is conceivable that the build-up of the inner disk is
caused by more frequent or more effective outbursts. During the
photometric bright state various other phenomena gain in prominence
and suggest this to be a phase of increased activity. Of particular
interest, but possibly only apparently related to this phase, are
absorption components at redshifts well beyond the range covered by
the combination of rotation and nonradial pulsation.