Possible HeI 6678 Emission Activity in  Cas
Ernst Pollmann1 and Berthold Stober2
1
Emil Nolde Straße 12, 51375 Leverkusen, Germany
email:
ernstpollmann@aol.com
2
Nelkenweg 1, 66907 Glan-Münchweiler, Germany
email:
dr.b.stober@dgn.de
Received: Dec 1, 2003; Accepted: May 16, 2005
I. Introduction
Spectroscopically
 Cas has been investigated mostly in the
Balmer lines, mainly in
H . Recent studies considered He and Fe lines
as well as the kinematics of the circumstellar shell
(Hanuschik 1995; Smith 1995).
It is believed that a local density
enhancement -- a one-armed density spiral -- is embedded in the circumstellar disk of
Cas. The precession of this density enhancement has been
observed interferometrically by Berio et al. (1999). They found that this
enhanced equatorial density pattern may be located at 1.5 stellar
radii from the star's surface. Stee et al. (2003) proposed that He
excitation and ionization, particularly HeI 6678, extend to 2.3
stellar radii. The probably time-dependent mass loss from the primary
component of the
Cas binary system allows us to assume that
both photospheric and disk density variations lead to the observed
double peak profile variations. Recent investigations of
Smith (1995), Harmanec et al. (2000), and Miroshnichenko et al. (2002) give detailed
information about long-term monitoring of the phase and time dependent
radial velocities and equivalent widths of the HeI 5875 and
the HeI 6678 lines.
II. Results
First spectra from Pollmann with a resolution R ~ 8500
come from May
2002 obtained with the grating spectrograph of the 200 mm
Schmidt-Cassegrain telescope of the Vereinigung der Sternfreunde Köln.
The spectra of Stober were taken with a 300 mm Newton telescope and a
Littrow grating spectrograph (R ~ 8000).
Usually, about 100 CCD spectra,
with integration times of 20--30 s were combined. Each single spectrum
has been carefully examined for cosmic rays. In case of any cosmic ray
appearence the respective spectrum has been rejected not to introduce
artificial flaws within the nightly sum spectrum. The complete data
reduction and equivalent widths measurement have been done according
to a standard procedure as already described by Pollmann (1997). The
accuracy of a EW measurement was determined in each sum spectrum
according to the method of Chalabaev & Maillard (1983). The size of the error bars
of individual data points correspond to the maximum standard deviation
of 14%. Our S/N ratio was always between 400 and 1600. To evaluate
the time behavior of emission activity and to reduce error bars, we
combined individual values of the equivalent widths of the violet
component EW(v) and the red component EW(r) to the sum EW(v+r) = EW(v)
+ EW(r) as presented in Fig. 1.
Figure 1.
Comparison of the time behavior of the HeI 6678 and
H emissions in the same time interval.
In Fig. 2 single spectra are combined as an "average normal spectrum"
for the period May 2002--March 2004 (JD 2452452--2453081).
Figure 2.
Comparison of the "average normal spectrum" to the
HeI 6678 absorption spectrum at JD 2453145 and maximum emission
spectrum at JD 2453220.
On May 19, 2004 (JD 2453145) we observed HeI 6678 only as weak
absorption of EW (v+r) = 25 mÅ but followed by a strong and short
outburst until about August 02 (JD 2453220) with a maximum of
EW (v+r) = -255 mÅ. To illustrate these two "events" the appropriate spectra
are printed together with the "average normal spectrum" in Fig. 2. For
clarification we show in Fig. 3 the extreme spectra at JD 2453145 and
JD 2453220 between 6500--6700 Å.
Figure 3.
Detail of the spectra of the "extreme events" at
JD 2453145 and JD 2453220 in the 6500--6700 Å section.
To find any correlation between HeI 6678 activity and
H
emission we show EW (v+r) and EW (H) in Fig. 1.
With our H error
bars of 5 Å we are not able to claim for any EW correlation
between these two lines within the time interval of JD 2453140--340. It
seems, that in certain exceptional cases
Cas shows a more or
less constant emission activity of the HeI 6678 line of 1--2% of the
continuum, as visible in our average normal spectrum and as seen by
Smith (1995). For this reason a further continuous monitoring seems
to be of large interest.
REFERENCES
Berio, P., Stee, Ph., Vakili, F., Bonneau, D., Mourard, D., Chesneau,
O., Thureau, N., Le Migrant, D., & Hirata, R., 1999, A&A, 345, 203
Chalabaev, A., & Maillard, J.P., 1983, A&A, 127, 279
Harmanec, P., P. Habuda, S. Stefl, P. Hadrava, D. Korcakova,
P. Koubsky, J. Krticka, J. Kubat, P. Skoda, M. Slechta, & M. Wolf, 2000,
A&A, 364, L85
Hanuschik, R. W., 1994, Proceedings of IAU Symposium 162, Eds. Balona,
L.A. et al., (Dordrecht:Kluwer), 265-266
Miroshnichenko, A.S., Bjorkman, K.S., & Krugov, V.D., 2002, PASP, 114,
1226
Pollmann, E., 1997, Be Star Newsletter, 32, 11
Smith, M. A. 1995, ApJ, 442, 812
Stee, Ph., Vakili, F., Bonneau, D., & Mourard, D., 1998, A&A, 332, 268
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