COMMISSION 27 OF THE I. A. U.
                INFORMATION BULLETIN ON VARIABLE STARS
                             Number 2495



                                                    Konkoly Observatory
                                                    Budapest
                                                    22 March 1984

                                                    HU ISSN 0374-0676


                          ON THE PERIOD OF AG PEGASI


  In the last time two periods of the well known symbiotic star AG Pegasi
were published, which are very different. Meinunger (1983) found a period of
827d from estimations of a large number of plates of the Sonneberg sky patrol
and from photoelectric measurements. This period is also well suitable for
reducing radial velocity data of the M-component of the star from JD ~~243 3000
to 244 2000. Slovak (1982), however, determined the period of 733d +- 30d from
visual observations of the AAVSO from JD ~~ 244 2000 to 244 4800 (1974 to 1982).
  To clarify this difference I examined further observations: visual estimations
of the AFOEV from JD ~~ 244 1000 until now and photoelectric measurements
made by the author with the Sonneberg 60 cm mirror II.
In addition to the minima of Meinunger two new minima were found:

   JD         epoch E_1  O-C_1
                        
2444650            20   -140d
5400               21   -217

The calculation of O-C_1 was carried out with the elements of Meinunger,

  (I) Min. = 242 8250 + 827d. E_1.

From E_1 = 17, JD = 2442360, a systematic negative  increase  of O-C_1 is
visible:

   JD         E_1   O-C_1  E_2   O-C_2
2442360       17   + 51d    0    -10d
   3150       18   + 14     1    +20
   3920       19   - 43     2    +30
   4650       20   -140     3      0
   5400       21   -217     4    -10



An improved representation of these minima is achieved by the following new
elements:

         (2) Min. = 244 2370 + 760d * E_2.

The other minima from E_1 = 0 to E_1 = 16 are well determined with equ. (1).
We suspect a period change near JD ~~ 244 3000. Therefore the origin of the
light variation cannot be explained simply by orbital motion, but should be
caused by a more complex mechanism. Further observations are necessary,
especially measurements of radial velocities, which should he examined with
the new elements.





                  R. LUTHARDT

                Sternwarte Sonneberg
                Zentralinstitut für
                Astrophysik der
                Akademie der 
                Wissenschaften der DDR
                64 Sonneberg, DDR





References:
                        
Meinunger, L., 1983: Mitt.Verand.Sterne 9, p. 92 [BIBCODE 1983MitVS...9...92M ]
Slovak, M.H., 1982: Journal of the AAVSO, Vol. 11, No. 2, p. 67 [BIBCODE 1982JAVSO..11...67S ]
Bull. AFOEV , No. 8 to No. 26