COMMISSION 27 OF THE I. A. U.
        INFORMATION BULLETIN ON VARIABLE STARS
                    Number 1952

                                  Konkoly Observatory
                                  Budapest
                                  1981 April 10

                                  HU ISSN 0374-0676


             ANOMALOUS V/R VARIATION IN EW Lac


   Hadrava et al. (1978), Harmanec et al. (1979), and Hirata and Kogure (1979)
reported that EW Lac (HD 217050, B2 IIIpe, shell) has shown a strong change
in its spectrum and colors in 1978, after a long stable shell-star phase.
Poeckert (1980) has made a detailed study on the radial velocity and line
strength changes in 1978 - 1979.
   We have examined the spectral variation of EW Lac for the period of
1973 - 1980, on about 60 spectrograms which were obtained at the Okayama
Astrophysical Observatory. Our examination has been made mainly on the V/R
relation of violet (V) and red (R) emission components and the asymmetric
feature of spectral line profiles. As the result we have found an anomalous
V/R variation which has begun in 1975 and is still lasting in 1980.
   The results of our inspection are summarized in Table I, where V/R relation 
is shown by an equality or an inequality between V and R components.
When no emission is seen, the letter N is used instead of the respective
V and R. The letters C and Z in the column of Sp denote the high- and low-
dispersion spectrograms, respectively, obtained with the following spectrograph:
C = coude spectrograph attached to the 188-cm reflector, the dispersion being
approximately 10 A/mm for Hbeta are bluer spectral region, and 20 A/mm for H_alpha.
Z = prism spectrograph attached to the 91-cm reflector, the dispersion is
72 A/mm at H_gamma.
   The asymmetric feature of the shell absorption profiles in higher members
of the Balmer series (H10 ~ H20) is given in Table I with the designation of:
sym = symmetric, asym = asymmetric, R-fade = the wing in the red side is
fading-out, and V-fade = the wing in the violet side is fading-out. In the
last column is given the principal quantum number n_l of the upper level of
the last visible Balmer lines. The value of n_l may be thought as an indicator
of the development of the shell-line forming envelope (Kogure et al, 1978).



             Table I. V/R variation of EW Lac



Epoch       Sp           V/R relation                   Profiles           
                 H_alpha H_beta   H_gamma H_delta H8   of higher           n_1 
                                                        members
1973 V      C      -     -           -     V~R    N=N   sym.                33
     XI     C      V=R   V=R         V=R   V~R    N=N   sym.                36
1974 VIII   C      V=R   V=R         V=R   V~R    N=N   sym.                36
     X      C      V=R   V~R         V~R   V~R    N=N   sym.                40
1975 XI     C      V=R   V=R         V~R   V>=R   V>=N  slightly asym.      34
                                                        (R-fade)
     XII    Z      -     V~R         V>=R  V>=R   -     (sym.)              -
1976 VIII   Z      -     V~R         V>=R  V>=R   -      sym.               -
     XI     C      -     V<=R        V~R   -      -     -                   -
1977 VIII   C      -     -           -     V>N    V>N   asym.(R-fade)       36
     X      C      V<=R  -           -     V>N    V>N   asym.(R-fade)       36
1978 XI     C      V~R   V>R         V>R   V>N    V>N   asym.(R-fade)       37
1979 V      C      -     -           -     V>N    N<R   nearly sym.         31
     VIII   C      V>R   -           V>R   V~R    N<R   asym.(V-fade)       32
     XI     C      V>R   V>R         V~R   V<R    N<R   asym.(V-fade)       35
1980 VII    C      -     -           V<R   V<R    N<R   asym.(V-fade)       -
     IX     Z      -     V>=R        V<R   N<R    N<R   asym.(V-fade)       -
     XI     C, Z   V>R   V<R         V<R   N<R    N<R   asym.(V-fade)       36
     XII    Z      -     V<R         V<R   N<R    N<R   asym.(V-fade)       -
                         



   From Table I we readily see that the asymmetric profiles can be traced
back as early as 1975 in H_delta and H_8, and, since then EW Lac seems to have
entered a new phase of anomalous V/R variation, which is characterized by a
kind of propagation of V/R relation from higher to lower members of the Balmer
series.
   The characteristic feature of this V/R variation may be stated as follows.
(1) Successive appearance of two opposite types of V > R and V < R propagation.
The first V > R propagation has started in 1975 from H8 and reached Ha about
4 years later. The duration of the same V > R relation for each Blamer line
is 2 ~ 4 years. The second V < R propagation has started in 1979 from HS and
reached H_beta in 1980. The time scale may be the same as before.
(2) Association with the asymmetric profiles of higher members of the Balmer
series. The first V > R propagation is related with the F-fade asymmetry,
whereas the second V < R propagation is with the V-fade asymmetry.
(3) Relationship with the value of n_l The value of n_l takes its minimum at
the onset of V/R propagation (n_l = 34 in 1975 and 31 in 1979) and increases
gradually up to its maximum at the end of the same phase of V/R propagation
(n_l = 37 in 1978).
   Complicated behavior of this anomalous V/R variation offers an interesting 
theoretical problem. If we adopt the eccentric rotating ring model
suggested by Huang (1973, 1975), the successive V > R and V < R propagation
may be explained qualitatively by adopting multiple eccentric rings whose major
axes are oriented to progressively rotated directions. Quantitatively, however,
this simple model involves many difficulties. Particularly, an important point
to be explained is why EW Lac has entered a new phase of  anomalous V/R 
variation after a long stable period. Further investigations observational as 
well as theoretical are much desired.


TOMOKAZU KOGURE, YOSHIAKI ASADA       MASAKAZU SUZUKI
and KIYOSHI ICHIMOTO
Department of Astronomy, University   Kanazawa Institute of
of Kyoto,                             Technology
Kyoto 606, Japan                      Ohgigaoka
                                      Kanazawa 920, Japan 



References:


Hadrava, P., Harmanec, P., Koubsky, P., Krpata, J., Zdarsky, F. 1978, IAU
   Circular No. 3317. [BIBCODE 1978IAUC.3317....2H ]
Harmanec, P., Horn, J., Koubsky, P., Zdarsky, F., Kriz, S. and Pavlovski, K.
   1979, IBVS No. 1555.
Hirata, R. and Kogure, T. 1979, IBVS No. 1575.
Huang, Su-Shu 1973, Ap. J., 183, 541. [BIBCODE 1973ApJ...183..541H ]
Huang, Su-Shu 1975, Sky and Tel., 49, 359. [BIBCODE 1975S&T....49..359H ]
Kogure, T., Hirata, R., and Asada, Y. 1978, Publ. Astron. Soc. Japan, 30, 385. [BIBCODE 1978PASJ...30..385K ]
Poeckert, R. 1980, Publ. Dom. Ap. Obs., Victoria, XV, 357.