COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                     Number 1363

                                   Konkoly Observatory
                                   Budapest
                                   1977 November 18


     OMICRON ANDROMEDAE: ANOTHER RECURRENT PHENOMENON ?



     Horn (1977) has reported that the absorption-shell components 
of the hydrogen lines have disappeared and that the emission 
components of Halpha have weakened and are below the continuum
level.

     We remark that this phenomenon has occurred about two
years after the appearance of the shell spectrum and of Halpha 
emissions. Furthermore, during the past shell-phase of omicron And, 
Slettebak (1952) observed a disappearance of the Halpha emissions in 1949,
three years after the beginning of the shell phase, that is at
about the middle of this phase.
     Now, if the shell features shall develop again, we may 
suppose that the dramatic changes claimed by Horn are a recurrent
phenomenon during the shell phases of omicron And. Its recurrence would
be of 28-29 years. A value close to this periodicity results from
the recurrent appearance of the shell spectrum (Fracassini and
Pasinetti, 1975). A rough value of this size is also exhibited
by a period analysis of the radial velocities from 1900 to
1976 (Fracassini et al., 1977).
     If the emphasized phenomenon is really recurrent, it may
be of interest for the right understanding of this shell phenomenon 
and for the construction of a suitable model.


    
                       M. FRACASSINI and L.E. PASINETTI
                       Osservatorio Astronomico di
                       Milano-Merate, Via Brera n. 28
                       20121 Milano, Italia

References:
Fracassini, M., Pasinetti, L.E., 1975, I.B.V.S. No. 1044
Fracassini, M., Pasinetti, L.E., Pastori, L., 1977 Astrophys.and Sp.
   Sci., 49, 145 [BIBCODE 1977Ap&SS..49..145F ]
Horn, J. 1977, IAU Circular No. 3122 [BIBCODE 1977IAUC.3122....4H ]
Slettebak, A. 1952, Astrophys. J., 115, 573 [BIBCODE 1952ApJ...115..573S ]




                   ERRATUM


In I.B.V.S. No. 1348 one of the references was incorrectly printed. 
It should read :

     Lorenzi, L.: 1977, Astron Astrophys. 55, 295