COMMISSION 27 OF THE I. A. U.
        INFORMATION BULLETIN ON VARIABLE STARS
                     NUMBER 381


                                  Konkoly Observatory
                                  Budapest
                                  1969 September 20


         TIMES OF MINIMA AND LIGHT ELEMENTS
                 OF S VELORUM


      S Velorum has been observed photoelectrically in
the UBV system at Cerro Tololo Inter-American Observatory,
Chile, with a 16 inch reflecting telescope. Since the
primary minimum of the system has a duration of about 15h
there is no possibility to observe the entire minimum
during an observing night. In two observing seasons four
times of minimum at partial phases were observed. 
Comparisons of individual observations at these phases with a
mean light curve give the following times of minimum for
each light curve.


Epoch T_1   V) JDhel 2438868.4994 +/- 0.0012 m. e.
            B)              .4983 +/- 0.0008
            U)              .4992 +/- 0.0015
Epoch T_2   V) JDhel 2438874.4334 +/- 0.0005
            B)              .4925 +/- 0.0007
            U)              .4314 +/- 0.0007
Epoch T_3   V) JDhel 2438880.3663 +/- 0.0003
            B)              .3662 +/- 0.0003
            U)              .3660 +/- 0.0009
Epoch T_4   V) JDhel 2439099.9121 +/- 0.0009
            B)              .9120 +/- 0.0004
            U)              .9110 +/- 0.0011.

      These values were averaged giving weights w = 2, 2,
and 1 for V, B, and U respectively, the results are:

       Minima                                   E   (O - C)
T_1)   JDhel 2438868.49911 +/- 0.00053 m.e.    -9   -0.00012d
T_2)   JDhel 2438874.43264 +/- 0.00071         -8   +0.00002
T_3)   JDhel 2438880.36620 +/- 0.00010         -7   +0.00013
T_4)   JDhel 2439099.91202 +/- 0.00037        +30   -0.00004

      A least square solution gives the linear light
elements:

      Min = JDhel 2438921.90199 +/- 5.9336663d . E
                        +.00014 +/-  .0000025 p.e.


      The minimum E = 0 of the linear photoelectric light
elements has been included with the older data as published
by O'Connell (1954); the assigned weight is w = 9. These
minima have been represented: a) by a linear ephemeris,
b) by a linear representation excluding Roberts' observations
(visual) before 1900, since O'Connell suggested
that an abrupt change in the period occurred then. And c)
a parabolic formula representing all times of minimum. The
least square solutions with an IBM 7040 computer are:

  a) Min = JDhel 2427612.3663 + 5.9336432d . E
                     +/-.0057 +/-.0000012 p.e.
  b) Min = JDhel 2431119.14527 + 5.93365874d . E
                     +/-.00074 +/-.00000097 p.e.
c) Min = JDhel 2427612.3560 + 5.9336475d . E + 4,47 10^-9 . E^2
                     +.0016   +.0000009        +.55 p.e.


                      [FIGURE 1]

	Figure 1: Residuals from eqs. a, b and c.

The residuals (O-C) are given in Fig.1. There is no
conclusive evidence that the period changed abruptly in
~1900, neither that the  period increases continuously.
However, more photoelectric data should be obtained in the
future.


1969 September 11


                         R. F. SISTERO
                      Cordoba Observatory
                         and I. M. A. F.
                     Laprida 854, Cordoba,
                          Argentina





Reference:

O'Connell D. J. K., S. J., 1954, Ric. Astr., 3, 90. [BIBCODE 1954RA......3...90O ]