COMMISSION 27 OF THE I. A. U. .
         INFORMATION BULLETIN ON VARIABLE STARS
                     Number 1687

                                     Konkoly Observatory
                                     Budapest
                                     1979 October 16



             PERIOD CHANGES OF RT PERSEI



     The rediscussion of the period changes of the close binary
system RT Persei performed by Frieboes-Conde and Herczeg (1973)
seems to be very interesting. They postulated a sudden change of
the orbital period occurring somewhere around JD 2419550 (1912).
Thus they were able to determine a light-time orbit which was in
good agreement with the existent minima.
     Now, if we keep up the hypothesis of a third component, it
seems necessary to postulate another sudden change in the orbital
period occurring somewhere around JD 2435433 (1956). That is why,
in order to build up the corresponding O-C diagram,the following
formulae are to be used:

     Min.hel. = JD 2419550.251 + 0.8494135d * E    t<1912
     Min.hel. = JD 2419550.251 + 0.8494061d * E 1912<t<=1956
     Min.hel. = JD 2435433.296 + 0.8494033d * E' t>1956

     As is known, RT Persei is a semi-detached close binary system
and the "observed" sudden period changes could be considered as
real facts.In such cases the evaluation of the periodic variation
caused by the presence of a third body will be very difficult.
We have tried to do that and the following empirical formulae
have been established:

(O-C)_c =0.017d sin(0.0195dE+81deg) + 0.0022d sin 2(0.0195degE+73deg), t<1956
    
(O-C)_c =0.017 sin(0.0195E'+85) + 0.0022 sin 2(0.0195E'+77), t>1956
   
     If the second postulated sudden change in the orbital period
was a real one, the corresponding light-time orbit would be 
characterized by the following constants:

        P' = 43 years,    a'sin i' = 3.04 a.u.
        e' = 0.26               to = JD 2432459
      omega=17deg              m_3 = 0.5 m_Sun.


                         [FIGURE 1]

                                 
    As we can see in Figure 1, new series of observed minima are
required in order to see if there is a satisfactory agreement 
between "observed" and computed O-C differences, and to prove if
the two postulated sudden changes in the orbital period are or
are not real.




                           IOAN TODORAN
                           Astronomical Observatory
                           Cluj-Napoca





Reference:
Frieboes-Conde, H., and Herczeg, T., 1973, Astron.Astrophys.
      Suppl. 12, 1-78 [BIBCODE 1973A&AS...12....1F ]