COMMISSION 27 OF THE I. A. U.
            INFORMATION BULLETIN ON VARIABLE STARS
                         Number 3696

                                                Konkoly Observatory
                                                Budapest
                                                19 February 1992

                                                HU ISSN 0374 - 0676


               MULTICOLOUR OBSERVATIONS OF 4 DRA


The variable star 4 Dra=CQ Dra=BS 4765=HD 108907 (V ~ 5m) is known as a unique
triple system containing an M3 giant (4 Dra A) and a cataclysmic binary (4 Dra
B), the latter being probably of magnetic type. Orbital period fur a wide pair
(A+B) is found to be 1703 days, while IUE observations reveal a photometric
period 3h 58.5m for a cataclysmic binary (Reimers et al., 1988). As argued by
Reimers (1985), the M giant spectrum dominates the spectrum of 4 Dra at lambda
> 3200 angstrom. However, UHV obrervations by Skopal et al. (1990), Urban &
Hric (1990) and Hric et al. (1991) have given the first optical detection of
the orbital motion within the wide pair of 4 Dra system. Besides the long-term
trends in U and B colours; the above-mentioned observers have discovered
irregular variability up to 0.15m on a time-scale of weeks and months with
general morphological similarity between all three colours.

In August 1991 we have carried out the photometric observations of 4 Dra in
Vilnius photometric system using the 1-m telescope and the single-channel
pulse-counting photometer at Mt. Maidanak in Usbekistan. 6 Dra= BS 4795=HD
109551 (V=4.89) was used as a comparison star. The results (Table 1) are
presented as differences between the variable and the comparison star in
stellar magnitudes in the instrumental system. The observational errors
range from <=0.01m to 0.04m varying from night to night and usually increasing
towards shorter wavelength:. The measurements have been corrected for
differential extinction using the mean extinction coefficients for Mt.
Maidanak by Zdanavicius & Macijauskas (1980). It should be mentioned that in
some cases the star was lying quite low in the sky (z ~=70deg) and the
extinction conditions extend up to 0.09m at shortest wavelengths. However,
possible errors arising from the use of mean extinction coefficients instead
of instantaneous ones cannot alter the general pattern of variability,
illustrated in Fig. 1. The most striking feature in Fig. 1 is the
well-pronounced variability in the U filter (centered at lambda = 3450 angstrom)
and analogous variations (but with smaller amplitude) up to the wavelength 4050
angstrom (filter X). At the same time the variations at longer wavelengths
(lambda >= 4660 angstrom) are quite moderate and they may even have an opposite
sign compared with that in U filter. However, our observing run is too short
for to conclude, whether the behaviour of 4 Dra was really somewhat different
from that described by Urban & Hric (1990) and Hric et al. (1991). It can be
mentioned that phases of our observations according to the ephemeris for the
wide pair by Reimers et al. (1988) are between 0.290 and 0.305.

   Table 1. Observations of 4 Dra in Vilnius photometric system

      JD      DeltaS  DeltaV   DeltaZ  DeltaY  DeltaX  DeltaP  DeltaU
2448471.307   -0.213   0.011   0.086   0.289   0.597   0.939   1.205
    472.365   -0.187   0.059   0.111   0.325   0.666   1.104   1.389
    473.302   -0.214   0.031   0.085   0.284   0.597   0.968   1.261
    476.330   -0.187   0.035   0.115   0.315   0.614   0.980   1.221
    478.399   -0.155   0.056   0.130   0.357   0.647   1.042   1.357
    479.203   -0.157   0.087   0.134   0.349   0.656   1.016   1.328
    482.278   -0.081   0.151   0.216   0.431   0.747   1.096   1.411
    487.252   -0.058   0.181   0.216   0.452   0.724   1.055   1.351
    489.296   -0.076   0.161   0.212   0.439   0.689   0.979   1.250
    490.406   -0.024   0.193   0.236   0.445   0.648   0.923   1.094
    492.380   -0.073   0.192   0.212   0.430   0.684   0.966   1.099
    493.258   -0.072   0.177   0.210   0.441   0.693   1.008   1.277
    494.231   -0.081   0.160   0.212   0.433   0.704   1.033   1.324
    496.189   -0.096   0.157   0.200   0.421   0.674   1.032   1.312
    496.273   -0.076   0.149   0.200   0.422   0.883   1.023   1.314

The triple system 4 Dra is a very bright star which deserves continuous
attention. The multicolour observations described above would be very useful
for finding out which role the hot component (cataclysmic binary) can play in
forming of the continuous spectrum of the triple system at lambda <= 4000
angstrom. Since January 1991 some UBV observations of 4 Dra have been carried
out at Tartu observatory as well. Results of them will be published later.

Finally, we are very grateful to Prof. V. Straizys for allotting observing
time on the telescope of the Institute of Theoretical Physics and Astronomy of
the Lithuanian Academy of Sciences and to Dr. S. Bartasiuté for her kind help
in observations.

                                 [FIGURE 1]

 Fig.1. Variability of 4 Dra in seven filters of the Vilnius photometric 
 system.



       L. LEEDJARV, O. KAAL, P. MUSTASAAR, K. VIRUNURM
       Tartu Astrophysical Observatory
       Toravere 202444
       ESTONIA

References

Hric, L., Skopal, A., Urban, Z., Dapergolas, A., Hanzl, D., Isles, J. E., 
   Niarchos, P., Papousek, J., Pigulski, A., Velic, Z., 1991, Contr. Astron.
   Obs. Skaln. Pleso, 21, 303. [BIBCODE 1991CoSka..21..303H ]
Reimers, D., 1985, Astron. Astrophys., 142, L16. [BIBCODE 1985A&A...142L..16R ]
Reimers, D., Griffin, R. F., Brown, A., 1988, Astron. Astrophys., 193,180. [BIBCODE 1988A&A...193..180R ]
Skopal, A., Hric, L., Urban, Z., 1990, Contr. Astron. Obs. Skaln. Pleso,
   19,123. [BIBCODE 1990CoSka..19..123S ]
Urban, Z., Hric, L., 1990, Contr. Astron. Obs. Skaln. Pleso, 20,121. [BIBCODE 1990CoSka..20..121U ]
Zdanavicius, K., Macijauskas, D., 1980, Bull. Vilnius Astron. Obs., 55,11. [BIBCODE 1980VilOB..55...11Z ]