COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                      NUMBER 658

                                      Konkoly Observatory
                                      Budapest
                                      1972 April 11


             ON THE BINARY SYSTEM CV Ser


CV Ser is a binary system involving a carbon Wolf-Rayet and an early type star.
After the discovery as a spectroscopic binary by Hiltner (ApJ 102, 492, 1945),
Gaposchkin (Per. Zv. 7, 36, 1949) found the star to be an eclipsing binary. In
1963 the photoelectric observations of Hjellming and Hiltner (ApJ 137, 1080,
1963) showed a 0.5m deep minimum during at least 10 days, with a period
P=29.640d (T_0=2437887.76). From that time no eclipse has been observed
(Stepien Ac. Astr. 20, 13, 1970; Kuhi and Schweizer, ApJ 160, 185L, 1970) in
either narrow bands (lambda>5500 A) or in UBV photometry, except for the
eclipses found by Tcherepaschuk (1969, AZ 509) in the strong CIII - CIV blend
at lambda 4652 (primary eclipse of 0.2m, secondary eclipse ~0.05m), but not
in the nearby continuum. On the other hand, Cowley and Hiltner (Astr. Aph.
11, 407, 1971) give a new period P=29.7055d (T_0=2440784.00) that may explain
the lack of eclipses in the observations of 1967-68-69.

In order to check the existence of the primary eclipse, photoelectric
observations of CV Ser have been made from May to August 1971 with the 40 cm
refractor of the Teramo Observatory. The observations were concentrated,
whenever possible, in the phase range corresponding to the foreseen primary
eclipse computed with both the old and the new period (29.^d640 and 29.^d7055,
respectively).

                          [FIGURE 1]

The measures have been made by comparison with BD -11deg4592, whose V magnitude
has been obtained by means of standard stars. BD -11deg4590 has been used as
check star. In the following table are listed the date (JD), the phase
(either with the old and the new period) and the V magnitude of CV Ser.

Date        Phase         Phase                V^+

2441        (P=29.640d)  (P=29.7055d)
  080.527    0.718         0.982             9.135
     .548     .719          .983              .142
  085.609     .890          .153              .144
  086.491     .919          .183              .153
     .552     .921          .185              .141
  108.473     .661          .923              .133
  130.404     .401          .661              .128
  134.400     .536          .796              .138
  136.538     .608          .868              .127
  141.430     .773          .033              .138
  144.433     .874          .134              .133
  146.406     .941          .200              .150
  147.483     .977          .236              .137
  156.426     .280          .537              .139
  174.336     .883          .140              .129
  175.337     .917          .174              .140
  176.373     .952          .209              .136

^+ Each V magnitude is a mean value of some integrations.

With the period P=29.7055d the curve is filled enough by the observations
(Fig. 1a), whose average results V=9.138+-0.007 (m.e.). The lack of eclipses,
evident at first glance on the light curve, is emphasized by the smallness of
the error. Considering a minimum lasting at least 10 days (Hiltner 1963), the
average of the points which fall in the corresponding phase range is V_min=
9.135m, quite brighter than the average of the points out of this range
(V_max=9.140m). With the period P=29.640d max half light curve (Fig. 
1b) is covered by the observations, but again no eclipse is evident.

An attempt has been made using both half and double value of the period, but
the light curves, which appear sufficiently filled by the observations, do not
show any type of eclipse. Therefore, the disappearance of the eclipses is
confirmed also in 1971 for the principal one; the disappearance of the
secondary minimum can be considered almost certain.


P. BURCHI
Osservatorio Astronomico
Teramo - Italy