COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                     Number 1931

                                  Konkoly Observatory
                                  Budapest
                                  1981 March 10

                                  HU ISSN 0374-0676



  CALL FOR SYSTEMATIC PHOTOELECTRIC OBSERVATIONS OF CX Dra



   CX Dra (HD 174237, HR 7084, SAO 031165) is a bright Be star
whose photometric variability was disclosed by Merlin (1975).
Koubsky (1976) found that the star is a single-line spectroscopic 
binary with a period of 6.69 days. In a detailed study, based
on photoelectric UBV measurements of the star obtained in the
period from 1964 to 1978, Koubsky et al. (1980) showed that at
least three different types of photometric variability are 
superimposed:
   1. Long-term variability with a range of 0.2m in V and B,
      and more than 0.3m in U,
   2. Periodic variations, with the orbital period of 6.696
      days, and amplitudes around 0.03m in all three colours,
      and
   3. Occasional night-to-night variations (up to 0.1m in V).
   In summer and autumn 1980 we observed CX Dra at Hvar
(Yugoslavia), Kryoneri (Greece) and Skalnate Pleso (Czechoslovakia) 
observatories. We have detected very remarkable photometric 
behaviour of the star. Already in July (JD 2444433-40)
the star was unusually bright (the V colour varying roughly 
between 5.8m and 5.9m). Such values were in the past detected only
by Merlin (1975) during twelve days in July 1974 (JD 2442228-40).
On August 24, 1980 (JD 2444476) the brightness of CX Dra 
increased to the following extreme values
   V = 5.68m, B-V = -0.02m and U-B = -0.73m.
In the fall of 1980 we detected values around 5.77m in V. The
long-term behaviour of the star is illustrated in the Figure,
where normal points (averaged over 10 to 50 days) are plotted.
A remarkable peculiarity of the brightening observed in 1980 is
that the U-B values remained almost constant and did not follow
the changes in the V colour as in all previously recorded cases.

                     [FIGURE 1]

   We thus appeal to all colleagues interested in the Be-star
photometry to secure as much photoelectric observations of CX
Dra as possible. Clearly, even simultaneous observations of 
different kinds would be of a great value. The star will soon be
well observable on the morning sky. We recommend to use HR 7060
(V = 6.187m, B-V = + 0.080m, U-B = + 0.132m) as the comparison
and HR 7028 (V = 5.994m, B-V = -0.069m, U-B = -0.232m) as the
check star, and to observe the check as frequently as variable.




P. HARMANEC, J. HORN, P. KOUBSKY

Astronomical Institute of the Czechoslovak Academy of Sciences,
251 65 Ondrejov, Czechoslovakia

J. ZIZNOVSKY

Astronomical Institute of the Slovak Academy of Sciences, 059 60
Tatranska Lomnica, Czeshoslovakia



References:
Koubsky, P.: 1976, Inf. Bull. Var. Stars IAU Com.27, No. 1188. [IBVS 1188]
Koubsky, P., Harmanec, P., Horn, J, Jerzykiewicz, M., Kriz, S. 
	Papousek, J., Pavlovski, K., Zdarsky, F.: 1980, Bull. Astr.
	Inst. Czech. 31, 75 [BIBCODE 1980BAICz..31...75K ]
Merlin, P.: 1975, Astron. Astrophys. 39, 139. [BIBCODE 1975A&A....39..139M ]