COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                  Number 1044

                            Konkoly Observatory
                            Budapest

                            1975 September 9


 CONFIRMATION OF THE PERIODICITY AND THE PERIOD (ABOUT 30 YEARS)
          OF THE SHELL OF OMICRON ANDROMEDAE


  The reappearance of the new shell of o And, reported in IAUC
n. 2802, 2810, 2814, confirms the periodicity of the shell of
o And, and the period suggested by Schmidt (1959) and by Pasinetti
(1967, 1968).
  o And was observed at Merate Observatory each year from 1961
to 1975. During this time, the Balmer lines showed sharp absorption 
cores, indicating a thin shell: The intensity of the cores
and the number of Balmer lines in which they appeared, were variable; 
sometimes the cores appeared from H_alpha to H_8. In the years
1963, 1964 the hydrogen-absorption cores completely disappeared.
The figure shows the situation of the shell (presence or absence)
of o And versus time. We constructed this graph with the simple
assumption that the time interval (about 11-12 years) between the
last presence of the shell spectrum (1951) and the complete 
disappearance of the hydrogen-absorption cores (1963), may be nearly
equal to the time interval between the observed absence of cores
and the reappearance of a new shell. Hence we suggest that the
new large shell should reappear about in 1976.
  The reported diagram has only a qualitative character, for the
observational material at our disposal presence, intensity, number 
of the Balmer absorption cores does not allow us to construct
an ordinate scale.
  From the figure we can deduce that the shell of o And has a
period of about 30 years. Our diagram is similar to that reported
by Schmidt (p. 261, Fig. 10); unfortunately this author does not
explain the meaning of the ordinate scale of his graph.
  Two spectrograms of o And obtained on July 23.966 UT 1975 in
the H_alpha-H_epsilon region with Zeiss prism-spectrograph (dispersion 35 A/mm
at H_gamma) of the 137 cm reflector, show: Balmer absorption cores

                          [FIGURE 1]

  _____ Phase surely determined; ... _ _ _ ... assumed periodicity:
 (triangle) B-type spectrum with sharp hydrogen absorption cores; X normal
 B-type spectrum, absence of Balmer cores; (triangle with line) B-type
 spectrum, the presence of Balmer cores has not been reported in the 
 literature; O shell spectrum: metallic absorption lines, sharp and deep 
 Balmer absorption cores, emission at H_alpha; (circle with line) shell
 spectrum, no emission at H_alpha.


similar to those observed in the preceding years (the cores visible
in September 1974 are sharper and deeper than those observed in
July 1975); H_alpha has a week absorption feature partly masked
from the emission dispersion at H_alpha ~ 200 A/mm ; weak metallic
absorption lines.
  The probable duplicity of o And has not been confirmed by our
diagrams of radial velocities (Galeotti and Pasinetti, 1968a, 1968b)
obtained with the photoelectric period proposed by Schmidt (1959).
No periodicity of radial velocities has been found also considering 
the period proposed by Olsen (1972). The duplicity of o And
was questioned by Detre (1966) (see Pasinetti, 1968).



                          M. FRACASSINI
                          L.E. PASINETTI
                      Osservatorio Astronomico de
                        Milano-Merate, Italy



References:

Detre, L. 1966, Private communication
Galeotti, P., Pasinetti, L.E. 1968a, Contr.Oss.Milano-Merate, n. 300
Galeotti, P., Pasinetti, L.E. 1968b, IAU I.B.V.S. No 301
Olsen, E.H. 1972, Astron.and Astrophys. 20, 167 [BIBCODE 1972A&A....20..167O ]
Pasinetti, L.E. 1967, Atti XI Riunione Soc.Astr.It., Padova
       7-9 Ottobre
Pasinetti, L.E, 1968, Mem.Soc.Astron.It. 39, 73 [BIBCODE 1968MmSAI..39...73P ]
Schmidt, H. 1959, Z. Astrophys. 48, 249 [BIBCODE 1959ZA.....48..249S ]