COMMISSION 27 OF THE I.A.U.
                 INFORMATION BULLETIN ON VARIABLE STARS
                             Number 3263

                                                        Konkoly Observatory
                                                        Budapest
                                                        18 November 1988

                                                        HU ISSN 0374 - 0676


        OMICRON AND: ANOTHER MAJOR SHELL PHASE JUST COMING?

The bright B6IIIe shell star omicron And (1 And, HR 8762, HD 217675, SAO
52609) has been observed spectroscopically and photometrically for
nearly a century. The Be shell star is the brightest component A of a
multiple system of at least four stars (see, e.g., Hill et al. 1988,
Harmanec et al. 1987 and Harmanec 1983, plus references therein).
Component B at a distance of about 0.3" apparently revolves in a common
orbit with A - the estimated orbital period is well over 100 years.
Component B itself is a double-lined spectroscopic binary with a period
of 33.08 days composed of two B6-B8 stars. There is a faint fourth
component a at a distance of some 0.05" for which no direct spectroscopic 
evidence has been found so far. If this component is also
gravitationally bound to A, the expected orbital period is about 10
years.
   Many investigators since the end of the 19th century have helped to
accumulate evidence of the gradual variations in the spectrum of omicron
And A from B-absorption to Be, Be shell, and vice versa. Horn et al. (1982)
demonstrated that the object becomes fainter during the development of a
new shell, similar to BU Tau, 88 Her or V1294 Aql. Harmanec (1984)-
compiling and analyzing all historical photoelectric photometry and most
of the available spectroscopic records - concluded that both - the light
minima and re-appearances of the hydrogen shell lines - are cyclic or
even periodic, with a cycle length of about 8.5 years. He also pointed


                          [FIGURE 1]


out the possible connection of this cycle with the expected orbital
period of subsystem Aa. Harmanec further concluded that the short-term
light variations of omicron And are periodic, with a period of 1.571 days,
but that the light curve varies in amplitude and shape along with the
8.5-year cycle. In particular, he noted that a well-defined double-wave
light curve with a full amplitude of 0.1m in V and B, reminiscent of a
close eclipsing binary, is usually observed during the presence of the
hydrogen shell lines.
   Gulliver et al. (1980) and Koubsky (1984) have shown that the
overall behaviour of the shell may be more complicated than simply
periodic. Koubsky stressed that the 8.5-year period is in a better
agreement with those shell events when also metallic shell lines were
observed. These were recorded in 1891, 1949-53, 1974-76 and 1981-83.
Should the suspected 8-9 year cycle be preserved, the first indications
of a new major shell phase must soon re-appear.
   Since the occurrence of the last major shell in 1981, omicron And has
been monitored systematically by a large group of photometric observers
associated with the International Be Observing Campaign (Harmanec, Horn
and Koubsky 1981). The results will be published elsewhere. Here, we
wish to report first preliminary results of the UBV observations of the
star secured by us with the 0.65-m reflector of the Hvar Observatory,
Yugoslavia in July, August and October 1988. They seem to indicate that
a new major shell phase may indeed be just coming.
   Fig. 1 is a plot of our preliminary V observations versus phase of
the 1.577-day period (the best-fit seasonal value of the period) shown
separately for the data secured before HJD 2447372 (Fig. 1a), between
HJD 2447373 and ... 387 (Fig. 1b) and in October (HJD 2447443-58) - Fig.
1c. It is seen that the variations displayed in Fig. 1a are somewhat
erratic, while Figs. 1b and 1c show a double-wave light curve of a
growing amplitude. (The comparison star was HR 8733, the V magnitude of
the check, 10 Lac was 4.88m, with a 0.02m scatter.) A full amplitude of
the rapid light variations in V as large as 0.10m (as seen in Fig. 7c)
has only been observed during the major hydrogen and metallic shell
phases, for the last time in 1981-83. Our observations may therefore
indicate a rapid development of a new major shell.
   We thus alert all northern-hemisphere observers to obtain as many
as possible new photometric, polarimetric, spectroscopic and magnetic
observations of o And before the star disappears from the winter sky.
   We thank M. Malaric, who helped to secure some of the observations.


          P. HARMANEC  1,
          P. HADRAVA  1,
          Z. RUZIC  2,
          K. PAVLOVSKI  2,
          H. BOZIC  2,
          J. HORN  2,
          P. KOUBSKY 1,2.


1) Astronomical Institute, 251 65 Ondrejov, Czechoslovakia
2) Hvar Observatory, 58450 Hvar, Yugoslavia



References:

Gulliver A.F., Bolton C.T., Poeckert R. 1980 Publ. Astron. Soc. Pacific 92,
   774 [BIBCODE 1980PASP...92..774G ]
Harmanec P. 1983 Hvar Obs. Bull. 7, 55 [BIBCODE 1983HvaOB...7...55H ]
Harmanec P. 1984 Inf. Bull. Var. Stars 2506
Harmanec P., Horn J., Koubsky P. 1987 IAU Com. 29 Be Newsletter 2, 3
Harmanec P., Hill G.M., Walker G.A.H., Dinshaw N., Yang S. 1987 Publ. Astron.
   Inst. Czechosl. No. 70, 115 [BIBCODE 1987PAICz..70..115H ]
Hill, G.M., Walker, G.A.H., Dinshaw, N., Yang, A., and Harmanec, P. 1988, Publ.
   Astron. Soc. Pacific. 100, 243. [BIBCODE 1988PASP..100..243H ]
Horn J., Koubsky P., Arsenijevic J., Grygar J., Harmanec P., Krpata J., Kriz
   S., Pavlovski K., 1982 IAU Symp 98, 315 [BIBCODE 1982IAUS...98..315H ]
Koubsky P. 1984 Inf. Bull. Var. Stars 2584