Central Bureau for Astronomical Telegrams
IAUC 3425: omicron Cet
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Read IAUC 3426
Circular No. 3425
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
TWX 710-320-6842 ASTROGRAM CAM Telephone 617-864-5758
omicron CETI
A. Cassatella, D. Gura, D. Reimers and D. Stickland report
that extensive IUE observations of omicron Cet AB have been made at
Viispa in the range 115-330 nm. The low-resolution spectra show a
continuum falling slowly toward shorter wavelengths. The rich
emission-line spectrum includes, in order of decreasing strength, Mg II
280.0 nm, C IV 155.0 nm, [C II] 232.5 nm, [Si III] 189.2 nm, [C III]
190.9 nm and Si II 180.8-181.7 nm. A large number of absorption
lines of Fe II, mainly originating from the ground state or low-lying
metastable levels, are also present. High-resolution long-wavelength
spectra show, in the range 260-290 nm, several violet-shifted
(by -60 km/s) dish-shaped Fe II absorption lines having a
full width of ~ 270 km/s. The Fe II resonance lines have an
additional narrow component at ~ +50 km/s, which is very close to that
found for the narrow component of the Ca II K line and to the radial
velocity of the star. The upper levels of the Fe II absorption
lines from ultraviolet multiplets 62, 63 and 64 coincide with those
of the Fe II emission lines occasionally observed in the optical
range. The Mg II resonance doublet has a P-Cyg profile similar to
that observed in V1668 Cyg (Cassatella et al. 1979, A.& Ap. 74, L18)
and to that reported by Joy (1926, Ap.J, 63, 336) for the H-gamma line in
omicron Cet. The halfwidth of the emission and the violet shift of the
P-Cyg absorption components both indicate an expansion velocity of
-350 km/s in the region where the lines are formed. Like the Fe II
lines, each Mg II line has two additional absorption components
superposed on the emissions at +50 and -60 km/s. The IUE low-resolution
observations indicate that the ultraviolet fluxes vary in
phase with the optical variations of omicron Cet A. The flux-distribution
variability shortward of 290 nm can be ascribed to omicron Cet B alone,
while the larger variations observed at longer wavelengths can at
least in part be due to omicron Cet A. No variability in the gross
features of the emission lines was noticed. The shape of the ultraviolet
continuum from omicron Cet B cannot be accounted for by any standard
stellar or blackbody energy distribution. Absorption by dust,
which is observed in the infrared up to 1" from omicron Cet A, could be
responsible for the anomaly. The possibility of explaining the
observed ultraviolet energy distribution and the spectral features
with an accretion disk around omicron Cet B is being studied. Ground-based
observations obtained simultaneously with the IUE observations
(Feb. 28, Aug. 17, Oct. 12-28) or during the past minimum will be
useful for this study.
1979 November 29 (3425) Brian G. Marsden
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