COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                     Number 1843

                                    Konkoly Observatory
                                    Budapest
                                    1980 September 16

                                    HU ISSN 0374-0676




           PERIOD CHANGE OF AW URSAE MAJORIS




     From a discussion of O-C for AW UMa, A-type contact binary,
Woodward et al. (1980) found that the times of minimum light obtained 
in 1978 indicated a significant period shortening. To examine 
this change of period all published photoelectric times
of minima were collected and used in calculations of elements
(References 1-4, 8-10).
     Two times of minima were determined recently in Cracow and
analysed by the procedure developed by Kwee and van Woerden (1956)
and listed in Table I. For this purpose, photoelectric observations 
in V colour were made using a 50 cm Cassegrain reflector
equipped with an EMI 9789QB and standard Schott filters.
                    Table I

           Times of minimum light for AW UMa

           J. D. hel        E_I             Observer

    2444292.5358+-0d0002   6744.5           Kurpinska
      44294.5093  0.0002   6749             Kurpinska

     In the behaviour of O-C diagram two linear parts were observed: 
one from the years 1963 to 1975 and second one from the
period 1978-1980. For these two parts linear elements of light
were determined by least-squares solutions:

I 1963-1975 JD_hel= 24 41333.51870+0.43873231.E 20phe obs.
                              +-20        +-5

II 1978-1980 JD_hel= 24 43948.79280+0.43872687.E 7phe obs.
                               +-13       +-19
     Figure 1 presents the O-C diagram calculated according to
the elements I. It can be seen in Fig.1 that the secondary minima 
show a larger dispersion than the primary ones which results
from the asymmetry of the light curve, occasionally appearing
near the secondary minimum (Dworak and Kurpinska 1975, Woodward 1980).

                         [FIGURE 1]

 Figure 1. O-C diagram for AW UMa. Filled and open circles refer to primary
 and secondary minima, respectively. Cross and cross in circle denote mean
 visual primary and secondary minima. The arrow marks the visual observations
 of Locher with O-C~~+0.04d.

     The decrease of period DeltaP=5.4d x 10^{-6} and the extremely low
mass ratio value q = 0.08, accepted by many authors, may be regarded 
as a possible proof for the relation DeltaP - q presented by
Kreiner (1977) for W UMa type stars. This relation seems to indicate 
that absolute period changes are increasing with the q
values.




                        MARIA KURPINSKA-WINIARSKA
                        Astronomical Observatory
                        of the Jagellonian University
                        31-501 Krakow,ul.Orla 171,Poland

References:
1. Diethelm, R. 1980, BBSAG 47
2. Dworak, T.Z. and Kurpinska, M., 1975, Acta Astron. 25, 417 [BIBCODE 1975AcA....25..417D ]
3. Geos EB7, List of minima
4. Kalish, M.S. 1965, Publ.Astron.Soc.Pac. 77, 36 [BIBCODE 1965PASP...77...36K ]
5. Kreiner, J.M. 1977, I.A.U. Coll.No.42, Bamberg [BIBCODE 1977ivsw.conf..393K ]
6. Kwee, K.K. and van Woerden, H. 1956, BAN 12, 327 [BIBCODE 1956BAN....12..327K ]
7. Locher, K. 1975, BBSAG, 28
8. McNamara, Stoke, 1979, I.B.V.S. No. 1701
9. Paczynski, B. 1964, Astron. J. 69, 124 [BIBCODE 1964AJ.....69..124P ]
10.Woodward, E.J. 1980, Astron.J. 85, 50 [BIBCODE 1980AJ.....85...50W ]