COMMISSION 27 OF THE I. A. U.
       INFORMATION BULLETIN ON VARIABLE STARS
                   Number 2830

                                  Konkoly Observatory
                                  Budapest
                                  4 December 1985

                                  HU ISSN 0374 - 0676


            PERIOD CHANGES IN R Leo




R Leo is one of the best known Mira-variables. Since
its discovery in 1782 this star was continuously 
observed by thousands of observers.
Irregularities in the period of R Leo were first discussed 
by Argelander (1869). Since then some other authors
(e.g. Turner and Blagg, 1915) reported changes in the
period. Later instantaneous elements were introduced
in order to satisfy the observer's needs 
(for a short review on instantaneous elements, see Hoffmeister et al.,
1984). During the last few years molecules, such as SiO,
OH and H2O, have been found in the circumstellar shell
(see e.g. Hjalmarson and Olofsson, 1979) and the 
interrelations with the period (Ukita, 1982) and light variations
(Le Squeren and Sivagnanam, 1985) were discussed. 
Recently Wood (1979) and Wood and Zarro (1981) studied the
general problem of period changes in Miras in the context 
of stellar evolution.
Because of the comprehensive material published on
R Leo (see Hoeppe, 1986), this star was chosen to prepare 
a study of its long-term variations. Due to the
topical significance first results are given here.
The author collected all the literature on R Leo
available to him (see Hoeppe, 1986).
The resulting (O-C)-diagram which covers 201 years of
observation (1782-1983) is shown in Figure 1. In 
obtaining the O-C residuals, the elements as described by
Kukarkin et al. (1969) were used in the slightly 
modified form

        Max. = J.D. 2362947 + 312.57d E.


                     [FIGURE 1]


The residuals' large variations are clearly visible. As
S Her, which was studied by Wood and Zarro (1981), R Leo
shows abrupt period changes, although the amplitude of
the O-C residuals is increasing in R Leo and is smaller
than in S Her. The graph seems to be nearly linear 
between the residuals maxima (at epochs 153 and 206) and
minima (at epochs 123 and 172).
In addition to Figure 1 some other results were derived
from the data. These are given in the following 
compilation:


   mean max. brightness = 5.76m +- 0.44m (n = 116)
   mean min. brightness = 9.96m +- 0.34m (n = 81)
   mean amplitude       = 4.14m +- 0.54m (n = 51)
   mean period       = 312.96d +- 15.86d (n = 112)
   mean M-m          = 138.23d +- 13.05d (n = 64)  
   

     
In this list the second value in each row indicates the
standard deviation.
In regard to the current research on helium-shell flashes
in Miras (see Wood and Zarro, 1981) extensive and continuous 
(O-C)-diagrams will provide a useful basis for
further studies.
More data and a more extensive discussion including a
study of some other long-term variations and the 
complete list of references to Figure 1 will be given in
a forthcoming paper (Hoeppe, 1986).

Acknowledgement
It is a pleasure for me to thank Professor Dr. Voigt
(Universitatssternwarte Gottingen) for his continuous
help, the valuable suggestions and comments, and for the
permission to use the library of Gottingen Observatory.


                             G.R. HOEPPE

                          Rudolf-Herzog Weg 9
                          3430 Witzenhausen 1
                          West Germany

References:


Argelander, F.W.A.: 1869, Astron. Beob. Sternw. Bonn 7, 361
Hjalmarson, A., Olofsson, H.: 1979, Astrophys. J. 234, L199 [BIBCODE 1979ApJ...234L.199H ]
Hoeppe, G.R.: 1986, in preparation
Hoffmeister, C., Richter, G., Wenzel, W.: 1984, Veranderliche 
 Sterne, 2nd ed., Springer, Berlin, p.73 [BIBCODE 1984vest.book.....H ]
Kukarkin, B.V., Kholopov, P.N., Efremov, Yu.N., Kukarkina,
 N.P, Kurochkin., N.E, Medvedeva., G.I., Perova., N.B.,
  Fedorovich, V.P., Frolov, M.S.: 1969, General Catalogue
  of Variable Stars, 3rd ed., Moscow, Nauka
Le Squeren, A.M., Sivagnanam, P.: 1985. Astron. Astrophys. 
 152, 85 [BIBCODE 1985A&A...152...85L ]
Turner, H.H., Blagg, M.A.: 1915, Mon. Not. R. Astron. Soc.
  76, 169 [BIBCODE 1915MNRAS..76..158. ]
Ukita, N.: 1982, Astron. Astrophys. 112, 167 [BIBCODE 1982A&A...112..167U ]
Wood, P.R.: 1979, Astrophys. J. 227, 220 [BIBCODE 1979ApJ...227..220W ]
Wood, P.R., Zarro, D.M.: 1981, Astrophys. J. 247, 247 [BIBCODE 1981ApJ...247..247W ]