COMMISSIONS 27 AND 42 OF THE IAU
              INFORMATION BULLETIN ON VARIABLE STARS
                           Number 4060

                                                  Konkoly Observatory
                                                  Budapest
                                                  8 August 1994

                                                  HU ISSN 0374 - 0676


        NEW PHOTOELECTRIC LIGHT CURVES OF VZ CANUM VENATICORUM


  The variability of VZ CVn was discovered by Strohmeier and Knigge (1960), who 
reported it to be a short-period variable star with an amplitude of 0.7m. In 1962 Strohmeier,
Knigge and Ott determined that VZ CVn was a beta Lyrae system with a deep secondary
minimum. From 22 epochs of primary minimum and 13 epochs of secondary minimum,
they derived the light elements:
            Min.I = JD_hel 2426002.700 + 0.8424635d x E             	(1)
  In 1965 Oburka reported three epochs of primary minimum for VZ CVn obtained
with binoculars. The first photoelectric light curves in BV bands were obtained in 1965
by Harris (1968), who got 2 epochs of primary minimum and 2 epochs of secondary
minimum. The epochs of these minima and the minima of other observers, together with
the weights assigned to them are processed with the aid of the least squares method. The
improved light elements are:
            Min.I=JD_hel 2426002.6956 + 0.84246261d x E           	(2)
  In 1971 and 1972 VZ CVn was observed photoelectrically by Ibanoglu (1974) in BV
bands, he observed 4 primary and 5 secondary minima. The epochs of these minima and
the minima of Harris and other observers were used together to determine improved light
elements by the method of least squares:
            Min.I=JD_hel 2438880.5807 + 0.84246150d x E                	(3)
  In 1972 Pohl and Kizilirmak reported 13 epochs of minima separately for each color,
in 1974 they published 2 epochs of minima, in 1977 they gave an epoch of minimum
again. From 1971 to 1976 Cester, Mardirossian and Pucillo (1977) observed VZ CVn in
UBV bands, 22 new epochs of minimum were deduced separately for each color from the
observations. All photoelectric minima were taken into account for a re-determination of
the light elements by means of least squares method, giving the same weight to the single
epochs and considering only the mean value of their U, B and V minimum. The new light,
elements are
           Min.I=JD_hel 2438880.5804 + 0.84246163d x E         		(4)
  The present observations of VZ CVn were made in BV bands on 7 nights from 1993
to t994 with photoelectric photometer attached to 1m reflecting telescope at Yunnan
Observatory, the comparison star and the check star are the same which have been used
by the previous observers: BD+29d2417 and BD+29d2409 respectively. The new light
curves (612 points in B and 610 points in V band) are displayed in Figures 1 and 2, all
the observational data have been corrected for the atmospheric extinction. The new light
curves were found to be variable near the maxima similarly to the observations of previous
observers. In addition, the new light curves showed some pulsational variations near the
maxima. From our observations an epoch of primary minimum and an epoch of secondary 
minimum were calculated and are listed in Table 1. In this table the O-C residuals
were computed according to Cester et al.'s light elements. 


                              [FIGURE 1]

            Figure 1. The light curves of VZ CVn in B band

                              [FIGURE 2]

            Figure 1. The light curves of VZ CVn in V band

                              [FIGURE 3]

                      Figure 3. The O-C diagram


  We collected all minima available, in order to calculate the O-C residuals using formula
(4). The O-C diagram is plotted in Figure 3. From this diagram a systematic trend, i.e.
decreasing period of VZ CVn is suspected. This is also seen when comparing formulae
(1) and (3). The detailed analysis of this system will be published elsewhere.



                           Gu SHENGHONG
                           Liu QUINGYAO
                           Yang YULAN
                           Wang BI
                           Huang ZHANKUI
                           Yunnan Observatory
                           Academia Sinica
                           Kunming, China



References:

Cester, B., Mardirossian, F. and Pucillo, M., 1977, A&A, 56, 75 [BIBCODE 1977A&A....56...75C ]
Harris, A. J., 1968, Astron. J., 73, 164 [BIBCODE 1968AJ.....73..164H ]
Ibanoglu, C., 1974, A&A, 12, 119 [BIBCODE 1974A&AS...13..119I ]
Kizilirmak, A. and Pohl, E., 1974, IBVS, No. 937
Oburka, O., 1965, Bull. Inst. Czech., 16, 212 [BIBCODE 1965BAICz..16..212O ]
Pohl, E. and Kizilirmak, A., 1972, IBVS, No. 647
Pohl, E. and Kizilirmak, A., 1977, IBVS, No. 1358
Strohmeier, W. and Knigge, R., 1960, Veroff. Remeis-Sternwarte Bamberg V, No. 6
Strohmeier, W., Knigge, R. and Ott, H., 1962, Veroff. Remeis-Sternwarte Bamberg V,
   No. 13