COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                     Number 1802

                                    Konkoly Observatory
                                    Budapest
                                    1980 June 12




    THE LIGHT VARIATION AND ORBITAL ELEMENTS OF AW UMa





    1. The eclipsing system AW UMa has been observed through
U, B, V and R filters from 1979 April 1 - 4 to 1979 May 4 - 6
using the 20 inch reflector of Urals University Observatory.The
comparison star was BD +30d2270. A total of 239 observations in
each filter were obtained. The extinction coefficient for each
filter was determined from the comparison star observations on
each night and all the observations have been corrected for 
atmospheric extinction. The mean errors of a single Delta m = m(var.)-
m(comp.) were calculated: 0.009m; 0.009m; 0.007m and 0.006m in U, B,
V and R, respectively. Epoch of primary minimum (determined by
the method of Pogson) is J.D.hel= 2443966.3420. No significant
difference was found between the times of minima determined From
the U, B, V and R light curves. The O-C = -0.0097 has been computed 
with the ephemeris by Dworak and Kurpinska (1975). The phases,
calculated from this ephemeris, were corrected by addition 0.0220
(what corresponds O - C =-0.00965). This value is arithmetical
mean from April series and May series of the Min 1 observations.
It is a very large value in comparison with O-C from the paper
of Dworak and Kurpinska and it shows a change of the period. The
individual observations are shown in Fig. 1 (dots represent April
dates and circles denote May dates). All four wavelength regions
show the difference in the heights of the maxima of the light
curves. Large differences from observations April 3 and April 4
were obtained for the phase interval 0.30 - 0.50. It is interesting 
that Dworak and Kurpinska obtained the deviation of their own
light curves from Paczynski's curve in the phaseinterval 0.25-0.45.
The polarimetric observations (Oshchepkov, 1974) shows the dependence 
of the observed polarization degree on the phase in the same

                        [FIGURE 1]

phase interval. All these effects show the existence of nonstationary 
processes in this close binary system.
    2. One of the authors (L.F. Istomin) derived the orbital
elements of AW UMa from the yellow light curve by the method of
Russell and Merrill (1952) and by the method of differential correction 
of Irwin (1947). Zero-point correction of -0.36m has been
applied. The phase interval 0.67-0.83 was taken for the determination 
of the constants of rectification, because at maximum light
at phase 0.25 a depression of light and large distortion of the
descending branch of the secondary minimum have been observed.
The final rectification in intensity then carried out as follow:

l_r=(1 + 0.0145 + 0.0138*cos(Theta)*cos(Theta))/(1.0153 - 0.1203*cos(Theta)*cos(Theta))

The term in the reflection effect A_1=+0.0013+-0.0027 was discount.
Constant term and the term cos(Theta)*cos(Theta) were obtained from preliminary
studies. For a limb-darkening coefficient of 0.6 the rectification
of the phase was made with z = 0.1153. The differential corrections 
for orbital elements a_1, a_2 and i were found by using the
complete descending branch and a part of the ascending branch
(0.05-0.14) of the primary minimum and the depth of the secondary
minimum. The final results are: {alpha_0}^{tr}= 1.2228 {alpha_0}^{oc}= 1.0      
k=0.2850+-0.0024 i=79deg+-1.1deg a_1=0.7059+-0.0030 a_2=0.2012+-0.0008

b_1= 0.6623 b_2= 0.1888 L_1= 0.94 L_2= 0.06 J_1= 1.27*J_2.
In Fig. 1 the solid line is the theoretical light curve in V.
Using b_1 and b_2 we find that the mass ratio M_2/M_1= 0.075, and
both components fill their Roche lobes (Plavec and Kratochvil,
1964).






L.F. ISTOMIN, L.M. ORLOV, V.V. KULAGIN

  Urals University Observatory

  Sverdlovsk, U.S.S.R.




References:
Dworak, T.Z. and Kurpinska, M., 1975, Acta Astron., 25, 417 [BIBCODE 1975AcA....25..417D ]
Oshchepkov, V.A., 1974, I.B.V.S. No. 884
Russell, H.N. and Merrill, J.E., 1952. Contrib.Princeton Univ.
  Obs. No. 26 [BIBCODE 1952deeb.book.....R ]
Irwin, I.B., 1947, Ap.J., 106, 380 [BIBCODE 1947ApJ...106..380I ]
Plavec, M. and Kratochvil, P.,1964, Bull.Astron.Inst.Csl., 15,
  No. 5, 165 [BIBCODE 1964BAICz..15..165P ]