COMMISSION 27 OF THE I. A. U.
        INFORMATION BULLETIN ON VARIABLE STARS
                    Number 2312

                                   Konkoly Observatory
                                   Budapest
                                   15 April 1983

                                   HU ISSN 0374 - 0676



      PHOTOELECTRIC MINIMA AND PERIOD CHANGES OF CO LACERTAE

  CO Lacertae (BD+56d2857) is an eclipsing system known by the short period
of the apsidal motion. The variable nature of CO Lac was announced by Zonn
(1933). The elements and apsidal motion period were given by Zonn (1936, 1950)
and Semeniuk (1967). The spectroscopic orbital elements were determined by
Smak (1967). Photoelectric observations and times of minima were published
by Kreiner (1968).
  During the period July 1981- August 1982, CO Lac was observed 
photoelectrically with the 50 cm reflector equipped with an EMI 9789 QB 
photomultiplier at Cracow Astronomical Observatory. The Schott filter GG-11 (in V region)
was used. The star "b" from the Wright's chart of CO Lac (Wright, 1937) was
used as a comparison star. No variation was detected in the light of the
comparison star.
  The times of minima obtained during the period of observations are listed 
in Table I.




                    Table I
-----------------------------------------------------
J.D. Hel.    Epoch       O-C_1     O-C_2   Remarks
2400000+
-----------------------------------------------------
44808.3533   11201     +0.0143d  +0.0018d  primary
       +-8
44821.4349   11209.5   -0.0129   -0.0004   secondary
       +-9
45171.5153   11436.5   -0.0136   -0.0019   secondary
       +-3
45181.5666   11443     +0.0134   +0.0017   primary
       +-5
-----------------------------------------------------


The epoch, O-C_1 and O-C_2 values have been calculated from the ephemeris
given by Semeniuk (1967):

Min. Hel.= J.D.2427534.0728+ 1.5422075d E                  (1)

                       [FIGURE 1]
            

Min. Hel. (prim.) = J.D. 242 7534.0728 + 1.5422075d E -
                        -0.0133d cos(157.7d + 0.0359d E)     (2)
Min. Hel. (sec. ) = J.D. 242 7534.8439 + 1.5422075d E +
                          +0.0133d cos(157.7d+0.0359d E)


  Fig. 1 shows the O-C_1 curve for all photoelectric times of minimum of
CO Lac published by Semeniuk (1967) and Kreiner (1968). The times of minimum 
light given in that investigation are also included. The full dots denote
primary minima, the open ones the secondary minima.
  The inspection of Fig. 1 leads to the conclusion that the Semeniuk's 
elements (2) are in good agreement with recent observations.



J.M. KREINER              MARIA KURPINSKA-WINIARSKA
Astronomical Department   M. WINIARSKI
Institute of Physics      Astronomical Observatory
Silesian University       of the Jagiellonian University
Katowice, Poland          Cracow, Poland



References:

Kreiner, J.M. 1968, Acta Astr., 18, 343. [BIBCODE 1968AcA....18..543K ]
Semeniuk, I. 1967, Acta Astr., 17, 223. [BIBCODE 1967AcA....17..223S ]
Smak, J. 1967, Acta Astr., 17, 245. [BIBCODE 1967AcA....17..245S ]
Wright, F. 1937, Harvard Ann., 89, 171. [BIBCODE 1937AnHar..89..171W ]
Zonn, W. 1933, Wilno Bull., 14.
Zonn, W. 1936, Wilno Bull., 17, 13.
Zonn, W. 1950, Torun Bull., 9, 18.