COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                     Number 2614

                                  Konkoly Observatory
                                  Budapest
                                  26 October 1984

                                  HU ISSN 0374 - 0676




          THE ABSENCE OF INTERCHANGES IN AC HERCULIS



  Several statements concerning AC Her published by C. Payne-Gaposchkin,
V. Brenton and S. Gaposchkin in their study of RV Tauri stars (Harvard Ann.,
113, No. 1, 1943) proved to be incorrect. These statements are "Interchanges
(between the primary and secondary light minima - G.E.) are quite uncommon,
for instance, for AC Herculis..." on page 37, the average interval between
the interchanges 50 epochs (with the total observation interval about 200
epochs) and the amplitude of fluctuation of light maxima 1.6m in the table
XVII. The statement in the paper by Preston et al. (Ap.J., 137, 401, 1963)
with reference to Harvard Annals 113, No. 1, 1943 is neither true that "...
the depth of secondary minimum for AC Her, as predicted from a uniform
ephemeris, was found to exceed that of primary minimum only five times in
a 40-year period." These statements were quoted partially by Magalashvili
and Kumsishvili (Abastumani Bull., No. 43, 1972), Nakagiri and Jamashita
(Tokyo Bull., No. 260, 1979), Baird (Ap.J,, 245, 208, 1981) and even GCVS
(1969).

   The revision of the photographic observations of AC Her from Payne-
Gaposchkin et al's paper showed that the interchanges of minima were not
detected. The period changes are small, therefore the possibility to 
miscalculate the predicted phases of primary and secondary minima can be 
excluded. The improved mean elements

         Min I=J.D. 2 435 052 + 75.439d E                      

were used. These elements were obtained by the author on the basis of 587
primary and secondary light minima. No shallow minima were observed at the 
phases of primary minima. The deepest secondary minima did not reach the
depth of primary ones. These minima are as follows.

   J.D.     I_pg   Number of obs. Phases
2 415 632   8.9        4           0.577
   16 155   8.94       1            .510 
   20 680   8.9        4            .491
   26 260   8.85       4            .457
   26 648   8.84       1            .600



The mean magnitudes of light extrema from Harvard observations are as follows:

        Min I  = 9.18m +- 0.08m
        Min II = 8.63  +- 0.10
        Max I  = 8.09  +- 0.18
        Max II = 8.28  +- 0.14

The mean quadratic deviations of the extrema are also given. The absence of
the interchanges between minima of AC Her was already noted earlier in my
paper (Variable Stars, Moscow, 18, 301, 1972). No interchanges were found
from numerous photoelectric observations of the recent years.




                        G.E. ERLEKSOVA


                      Astrophysical Institute
                   of Academy of Sciences of Tadjik SSR
                      Dushanbe, 734670, USSR