COMMISSION 27 OF THE I. A. U.
          INFORMATION BULLETIN ON VARIABLE STARS
                   Number 1176

                               Konkoly Observatory
                               Budapest
                               1976 September 10


PHOTOELECTRIC DIFFERENTIAL PHOTOMETRY OF THE CONTACT BINARY AW UMa


    The W UMa type contact binary AW UMa had been largely ignored
until recently. Attention has been drawn to this interesting system
by the excellent work of Dworak and Kurpinska (1975). We report 
additional observations obtained incidential to a program reported
elsewhere (McMillan et al. 1976). They were obtained with the McDonald
Observatory 91 cm reflector using a convencional single channel pulse
counting photometer. The data of Table 1 were obtained with a dry ice
refrigerated EMI 9658a together with a Stromgren y filter while 
Table 2 data were obtained with a dry ice refrigerated 1P21 and standard 
Johnson V filter. Two comparison stars (BD +30 2163, BD +33 2123)
were observed in sequence with the program star and were used to correct 
for slow sensitivity and transparency changes. The observational
and reduction techniques are described further in McMillan et al. (1976).
    The data of Table 1 are of extraordinarily high precision (1sigma =
= 0.001m formal error on the comparison stars) while those of Table 2
are of somewhat lower quality (1sigma = .035). The tables list heliocentric 
time of observation, phase calculated from the ephemeris of
Dworak and Kurpinska (1975), and our differential magnitudes with an
arbitrary additive constant.
    We confirm the Dworak and Kurpinska (1975) ephemeris. In addition 
it would be of interest to compare the accurate data of Table 1
with the Dworak and Kurpinska (1975) normal points. We have 
transformed our differential y magnitudes to their V system by solving for
the additive constant to make our data agree with their values. Second
order differences between our y and their V should be negligible since
intrinsic color variations are quite small for stars of this type.
Our data usually agree with their normal points to within 0.004m 
although we have found potions of the light curve which had changed.
In particular, our data near phase 0.075 are systematically 0.015m
brighter than their values, in agreement with the larger noise in
their normal points at this phase.

                      [FIGURE 1]

                     Table 1
JD hel      Phase*   Delta y   JD hel        Phase  Delta y
2442000+.              mag.   2442000+                 mag.

53.9086     .9798    -.1321   53.9732        .1270   .0290
53.9114     .9862    -.1254   53.9766        .1350   .0363
53.9141     .9925    -.1310   53.9787        .1397   .0474
53.9169     .9988    -.1306   53.9822        .1476   .0556
53.9197     .0052    -.1351   53.9850        .1540   .0625
53.9225     .0115    -.1291   53.9877        .1603   .0713
53.9252     .0178    -.1269   53.9947        .1761   .0853
53.9280     .0242    -.1244   53.9982        .1840   .0926
53.9329     .0352    -.1217   54.0023        .1935   .1019
53.9357     .0416    -.1181   54.0058        .2014   .1064
53.9391     .0495    -.1156   54.0086        .2078   .1077
53.9419     .0558    -.1102   54.0121        .2157   .1125
53.9447     .0622    -.1018   54.0148        .2220   .1140
53.9475     .0685    -.0924   54.0176        .2284   .1159
53.9509     .0764    -.0765   54.0211        .2363   .1166
53.9537     .0827    -.0640   54.0239        .2426   .1177
53.9565     .0891    -.0511   54.0273        .2505   .1155
53.9593     .0954    -.0348   54.0308        .2584   .1132
53.9614     .1001    -.0218   54.0336        .2648   .1124
53.9648     .1081    -.0075   54.0378        .2743   .1082
53.9676     .1144     .0050   54.0412        .2822   .1052
53.9704     .1207     .0184

Table 2
JD hel      Phase    DeltaV   JD hel        Phase    DeltaV
2442000+                     2442000+

205.6522    .8482    .1522   205.6988       .9543     -.0391
205.6550    .8546    .1228   205.7029       .9638     -.0233
205.6578    .8609    .1146   205.7071       .9733     -.0527
205.6613    .8688    .1466   205.7099       .9796     -.0792
205.6640    .8751    .1040   205.7126       .9859     -.0520
205.6668    .8815    .0891   205.7154       .9923     -.0562
205.6703    .8894    .0514   205.7182       .9986     -.0317
205.6731    .8957    .0440   205.7210       .0049     -.0687
205.6751    .9005    .0295   205.7231       .0097     -.0429
205.6786    .9084    .0147   205.7258       .0160     -.0537
205.6821    .9163   -.0016   205.7286       .0223     -.0561
205.6849    .9226   -.0203   205.7321       .0302     -.0539
205.6876    .9289   -.0201   205.7349       .0366     -.0196
205.6918    .9385   -.0447   205.7383       .0445     -.0158
205.6960    .9479   -.0295   205.7939       .0572     -.0189

* From JD hel Min I = 2438044.7812+ 0.4387334 E.

                                       G. J. FERLAND
                                       R. S. McMILLAN
                                       McDonald Observatory and
                                       Dept. of   Astronomy,
                                       University of Texas,
                                       Austin, Texas, 78712
                                       U.S.A.  
References:
Dworak, T.Z. and Kurpinska, M., Acta Astr. 25, No. 4, 417 [BIBCODE 1975AcA....25..417D ]
McMillan, R.S., Breger, M., Ferland, G.J, and Loumos, G.L., 1976,
              P.A.S.P. in press [BIBCODE 1976PASP...88..495M ]