COMMISSION 27 OF THE I. A. U.
      INFORMATION BULLETIN ON VARIABLE STARS
                   NUMBER 774

                                   Konkoly Observatory
                                   Budapest
                                   1973 March 15


     ON THE VARIABILITY OF Theta CORONAE BOREALIS


The first indication of photometric variability of theta CrB
has been reported by T.P. Roark(1). According to his four-colour 
ubvy and H_alpha -filter observations on June 16,17,18 and 19,
1970 theta CrB showed rapid variations as large as 0.7m in the u
and v bands. But at the same time the star was nearly constant
when observed in the y and H_alpha filters. On June 20, September
15 and 16,1970 the star did not show significant light 
variations in any colours.
Our UBV photoelectric observations of beta CrB could be used
to check the variability of theta CrB as this star was used as a
comparison star together with another one - mu BooA. These UBV
observations were obtained with the 13" reflector of the 
Simeis Branch of the Crimea Observatory on 21 nights between June
22 and August 24, 1970. Adopting for mu Boo A_v=4.29m, B-V=0.32m,
U-B=0.04m (2) UBV values for theta CrB have been obtained. They are
given in Table 1, showing no significant light variations of
theta CrB in any wave band during the observations.
On July 1971 the Bureau for Astronomical Telegrams informed 
that on June 29 and July 2 P. Couteau observed theta CrB as a
double star with a companion at the distances 0.46" and 0.47" of
brightness 5.5m and 6.7m, respectively (3). But on May 10   the
star under consideration was observed as a single one. On July
9 C.E. Worley observed the companion at 0.55" with Delta m_v ~ 2.5m(4).




                Table 1
-------------------------------------------
1970     UT      V        B-V      U-B    n
-------------------------------------------
June     22.3   4.130   -0.122   -0.560   5
         23.3   4.135   -0.118   -0.570   5
         26.3   4.130   -0.118   -0.550  10
         27.3   4.120   -0.128   -0.558   7
         30.3   4.128   -0.127   -0.581   6
July      4.3   4.129   -0.139   -0.580   7
          5.3   4.131   -0.127   -0.581   9
          6.3   4.130   -0.124   -0.577   4
          7.3   4.131   -0.112   -0.564   5
         11.3   4.130   -0.121   -0.560   8
         15.3   4.121   -0.117   -0.548   7
July     16.3   4.123   -0.115   -0.577   4
         17.3   4.124   -0.115   -0.569   8
         26.3   4.130   -0.112   -0.524   8
August    3.3   4.121   -0.122   -0.560   4
         10.3   4.137   -0.127   -0.536   7
         14.3   4.136   -0.130   -0.565   7
         17.3   4.124   -0.116   -0.552   7
         20.3   4.139   -0.115   -0.555   7
         22.3   4.132   -0.130   -0.563   7
         24.3   4.118   -0.116   -0.569   5
-------------------------------------------


                   [FIGURE 1]


    Later on it was communicated that K. Locher estimated on
panchromatic plate taken on June 24, 1971, that theta CrB was
by 0.5m brighter than usually (5).
    From July 8, 1971 after the announcement of Couteau's
observations theta CrB was observed by R. Burchi and P. Tempesti
at Teramo Observatory (6). Their observations did not show
any brightness variations of theta CrB.
    In summer 1971 our observations of beta CrB were continued
using only one comparison star theta CrB. Taking into account the
regular, and well known variability of beta CrB from previdious
observations with an amplitude as small as 0.03m it was possible 
to check the constancy of theta CrB using now beta CrB as comparison
star. The results are given in Table 2. No light variations
of theta CrB are to be found, confirming the results of R. Burchi
and P. Tempesti. For illustration the results of Teramo and
Crimean observations are plotted in Fig. 1. Locher's magnitude 
of June 24, 1971 and the magnitudes of June 29, July 2
and 9, 1971 given by Couteau and Worley are also plotted.
   Further regular photographic observations of theta CrB and
the check of its visual duplicity are of great interest.




         Table 2
-----------------------
1971    UT     V      n
-----------------------
June   12.3   4.133   5
       13.3   4.142   5
       14.3   4.139   9
       15.3   4.134   9
       16.3   4.127   7
       25.3   4.134   6
       28.3   4.133   6
       30.3   4.135   6
July    5.3   4.125   8
        6.3   4.124   5
        7.3   4.118   7
        8.3   4.118   6
       29.3   4.130   8
-----------------------




                       E.S. BRODSKAYA
                     Crimean Astrophysical
                        Observatory



References:

(1.) T.P. Roark, Astron.J. 76, 634, 1971. [BIBCODE 1971AJ.....76..634R ]
(2.) Tolbert, C.R., Astrophys.J. 139, 1105, 1964. [BIBCODE 1964ApJ...139.1105T ]
(3.) Couteau, P., Circ.Bur. cent.int.Telegr.astr. n. 2339, 1971. [BIBCODE 1971IAUC.2339....1C ]
(4.) Worley, C.E., Circ.Bur.cent.int.Telegr.astr. n. 2340, 1971. [BIBCODE 1971IAUC.2340....1W ]
(5.) Locher, K., Circ.Bur.cent.int.telegr.astr. n. 2342, 1971. [BIBCODE 1971IAUC.2342....1T ]
(6.) Burchi R. and Tempesti P., IBVS n. 619, 1972.