COMMISSION 27 OF THE I.A.U.
                INFORMATION BULLETIN ON VARIABLE STARS
                            Number 3204

                                                      Konkoly Observatory
                                                      Budapest
                                                      20 June 1988

                                                      HU ISSN 0374 - 0676


                  PLEIONE AGAIN WITHOUT SHELL

Pleione (BU Tauri = HD23862 = HR1180 = 28 Tau: B8Ve, Vsini = 341 km s^-1)
is a well known Be/shell star. It has been widely explored for nearly one
century and during this time underwent through different (Be, shell and
normal B) phases. Full description of the variations and discussion on the
observations of Pleione can be found in Gulliver (1977) and Doazan (1982).
After a shell phase from 1938 to 1954 the star entered a Be phase with strong
hydrogen emission lines exhibited in its spectrum (Morgan et al., 1973). In
the course of this Be phase emission lines of Fe II had also been present.
In December 1972 Pleione entered a new shell phase and since then the shell
strength had been found continuously increasing till 1981. Recently Goraya
et al. (1987) reported about increase of the brightness of Pleione at two
wavelengths (3300 and 3600 A) after 1981. This increase may be considered
as a first precursor of the shell phase end which is in agreement with the
conclusions of Doazan (1982) about the photometric behaviour of Pleione
in the time of previous phase changes.
   Pleione was among the stars included in the Be star observing programme
carried out in the National Astronomical Observatory "Rozhen". During the
autumn season of 1987 six plates were obtained with the coude spectrograph
of the 2m RCC telescope in NAO. Some data for them are listed in Table I.


                               Table I

Plate No.   JD_hel 2447000+   Spectral range (A)   Dispersion (A/mm)

2c2920         26.545           3350- 4900                9.0
2c2925         39.573           3450- 5000                9.0
2c2928         40.575           3450- 5000                9.0
2c2933         43.586           3450- 5000                9.0
2c2954        164.267           3350- 4900                9.0
2c2965        167.317           4800- 6800               17.8

   Our observations showed that significant changes happened to Pleione in
1987. In Figure 1 the shell spectrum of the star and its spectrum after the
shell lines had disappeared is compared. One can see that instead of the huge

                               [FIGURE 1]

 Figure 1   Density tracings of Hgamma region of Pleione's spectrum with and
 without shell lines.

                               [FIGURE 2]

 Figure 2   Radial velocities of the Balmer lines' absorption cores.


amount of sharp shell lines only a few shallow lines, mainly of singly ionized
metallic ions, have remained. There is no evidence of the broad absorption
of the Ca II K line, which was present in the star's spectrum in the time of
the last shell phase (Gulliver, 1977: Hirata and Kogure, 1976, 1977). No He
absorption lines are noticeable. Balmer absorption lines are visible up to
H_20. On all our plates they have significant asymmetry in their profiles with
the violet wing widened. One has to mention that the lower Balmer lines have
greater asymmetry than the higher. The low members also show double peaked
emission which is seen up to H_delta. Throughout the period of observations
the V component of the hydrogen emission was less than the R component. On the
2c2965 plate from 6/7, January 1988 some Fe II lines can be seen to have
P Cygni type profiles with weak red-wing emission. The strongest among them
are the Fe II lines at 4923.92, 5018.43, 5169.03, 5316,61 and 5891.36 A. It
must be noticed that Fe II emission were formerly present in the spectrum
of Pleione when hydrogen emission lines reached their maximal intensity
during the previous Be phase in 1954-1972. All our plates were measured for
radial velocities with the oscilloscopic comparator device in NAO. The radial
velocities were measured at the minima of the line profiles. On all the
plates there was found remarkably great Balmer progression with the lower
members less blueshifted (Figure 2). The observed progression is bigger than
that reported for the preceding phases (Gulliver, 1977: Ballereau, 1980).
Throughout the period of the observations no significant variations in the
radial velocities of the hydrogen and metallic spectral lines were detected.
   Even from this very preliminary results it is clear that Pleione is
undergoing quick evolution now, caused by the expansion of its shell. The
question now is how it will continue and the answer could be obtained only
from further observations.


   L. ILIEV and B. KOVACHEV                       M. RUUSALEPP

  Bulgarian Academy of Sciences,            Academy of Sciences of the
   Department of Astronomy and                     Estonian SSR,
National Astronomical Observatory,        Tartu Astrophysical Observatory,
 BG-4700 Smoljan, P.O.Box 136,             Toravere 202444, Estonian SSR,
          Bulgaria                                      USSR



References:

Ballereau, D., 1980, Astron. Astrophys. Suppl. Ser. 41, 305. [BIBCODE 1980A&AS...41..305B ]
Doazan, V., 1982, in "B Stars With and Without Emission Lines", eds. A.
   Underhill and V. Doazan, NASA SP-456, 340. [BIBCODE 1982bsww.book.....U ]
Goraya, P.S., Tur, N.S. and Rautela, B.S., 1987, Comm. 27 IAU 
   Inf.Bull.Var.Stars, 3052.
Gulliver, A.F., 1977, Astrophys. J. Suppl. Ser., 35, 441. [BIBCODE 1977ApJS...35..441G ]
Hirata, R. and Kogure, T., 1976, Publ. Astron. Soc. Japan, 28, 509. [BIBCODE 1976PASJ...28..509H ]
Hirata, R. and Kogure, T., 1977, Publ. Astron. Soc. Japan, 29, 477. [BIBCODE 1977PASJ...29..477H ]
Morgan, W. W., White, R.A. and Tapscott, J.W., 1973, Astron, J., 78, 302. [BIBCODE 1973AJ.....78..302M ]