Central Bureau for Astronomical Telegrams
IAUC 5539: zeta Tau
The following International Astronomical Union Circular may be linked-to from your own Web pages, but must not otherwise be redistributed (see these notes on the conditions under which circulars are made available on our WWW site).
Read IAUC 5540
Circular No. 5539
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
Telephone 617-495-7244/7440/7444 (for emergency use only)
TWX 710-320-6842 ASTROGRAM CAM EASYLINK 62794505
MARSDEN@CFA or GREEN@CFA (.SPAN, .BITNET or .HARVARD.EDU)
zeta TAURI
D. Ballereau, J. Chauville, A. M. Hubert, and J. Zorec,
DASGAL, Observatoire de Meudon et Institut d'Astrophysique, Paris,
write: "The well known Be star zeta Tau exhibits alternating
periods of quiet and active shell phases. According to Mon et al.
(1992 Feb., Be Newslett. 25), the long-term, pseudo-periodic
variation of the radial velocities of the shell lines and of the V/R
wavelength band ratio of the double-peaked emission of the first
Balmer lines has terminated since 1980, and the star has entered a
new quiet phase. Recent spectroscopic observations (1992 Jan. 18)
by D. Ballereau, at the European Southern Observatory 1.52-m telescope
(+ echelle spectrograph + CCD camera) in the blue wavelength
range, have revealed that the quiet phase has probably ended.
Indeed, the radial velocity (VR) of the metallic shell lines (Fe II,
Ti II, Cr II) has become strongly positive, with VR(mean) = +48.9
km/s, VR(H-gamma) = +39 km/s, and VR(He I) = +38 km/s. The H-gamma
line profile presents a deep shell core flanked by a weak but sharp
blue emission (VR = -103 km/s) and possibly a very weak red emission
(VR = +209 km/s); the V/R ratio of the blue and red emission
components of the H-gamma line is quite in agreement with the
positive radial velocity value of the shell absorption core, and the
displacement of the whole emission to red wavelengths, as is generally
observed in V/R variable shell stars. Once-ionized metallic
shell absorption lines are strongly bluewinged with a very sharp
core. A weak and narrow shell feature is present in the photospheric
He I 447.1-nm line profile. The Mg II 448.1-nm line has a
different structure, with a broader and symmetric shell component,
of VR = +19 km/s. Recently, Slettebak et al. (1992, Ap.J. Suppl.
Ser., in press) have found that, from 1989 Jan. to Oct., the V/R
ratio changed slightly from 1.02 to 0.97. This situation can be
compared with that previously reported by Hack (1955, Mem. Soc.
Italiana 26, 41), who noticed changes in the V/R ratio during the
1951-1952 campaign before the start of the active phase in 1954-
1955. Thus, looking into the history of zeta Tau, we can consider
that this star has now entered a new active shell phase. It would
be desirable that this interesting shell star be monitored with
different observational techniques in order to understand better
the mechanism of production of alternating active and quiet shell
phases."
1992 June 10 (5539) Daniel W. E. Green
Read IAUC 5540
Our Web policy. Index to the CBAT/MPC/ICQ pages.
