COMMISSIONS 27 AND 42 OF THE IAU
             INFORMATION BULLETIN ON VARIABLE STARS
                          Number 3884

                                            Konkoly Observatory
                                            Budapest
                                            21 May 1993

                                            HU ISSN 0374 - 0676


     COMPLETE BVRI LIGHT CURVES OF THE VERY SHORT PERIOD
                 W UMa VARIABLE YZ PHOENICIS


YZ Phoenicis (S7172) was discovered by Hoffmeister (1963).  His paper includes
a finding chart.  Gessner & Meinunger (1975) determined seven timings of
minimum light, and calculated a period of 0.3052d.  Jones (1989) presented
UBVRI photoelectric observations covering the primary eclipse and determined
standard magnitudes at two orbital phases.  Kilkenny & Marang (1990) published
a complete V photoelectric light curve and determined nine epochs of minimum
light.  They found Gessner & Meinunger's period to be in error, and
recalculated it to be 0.234727d, making YZ Phe one of the shortest period
nondegenerate binaries known.

The present observations of YZ Phe were made on 1989, November 2-8, inclusive,
at Cerro Tololo InterAmerican Observatory, Chile.  The 1.0-m Yale Reflector was
used in conjunction with the ASCAP photometer housing a dry-ice cooled
Hamamatsu R943-02 GaAs PMT with standard Johnson-Cousins BVR_cI_c filters.

The coordinates of the check, comparison, and the variable stars are given in
Table I.  From 450 to 500 observations were taken in each pass band.

                    Table I

Star         R.A.          Dec.
             (2000)        (2000)
             h  m  s        o  '  "
YZ Phe       01 42 22.6   -45 56 56
Comparison   01 42 28.8   -45 52 35
Check        01 42 21.4   -45 53 54

Four precise epochs of minimum light were calculated from observations made
during three secondary and one primary eclipses.  The bisection-of chords
method was used.  Our epochs of minimum light are shown in Table II along with
the one by Jones (1989).

 Table II
 JD Hel.      Min.  Cycles    (O-C)_1   (O-C)_2    Source
(2440000-I-)
5621.3968     I        0.0   -0.0008    0.0001     Jones
7832.6428(7)  II    9420.5    0.0001    0.0003     Pres. Obs.
7833.8166(4)  II    9425.5    0.0003    0.0002     Pres. Obs.
7834.7557(13) II    9429.5    0.0005    0.0005     Pres. Obs.
7836.7515(5)  I     9438.0    0.0011    0.0011     Pres. Obs.


                             [FIGURE 1]

 Figure 1. Intensity light curves of YZ Phe as defined by the individual
 observations and a preliminary light curve solution (solid line).


All available timings of minimum light were introduced into a least squares
solution to obtain the linear ephemeris:

         JD Hel. Min.=2445621.3976+0.23472963d * E (1)
                               +-9        +-8

A second ephemeris determined from photoelectric epochs only:

         JD Hel. Min.=2445621.3968+0.23472703d * E (2)
                          +-5             +-5

The period of the system has remained fairly constant over the thirty years it
has been observed.  Ephemeris (1) was used to calculate (O-C)_1 residuals in
Table II, and ephemeris (2) was used to phase our observations and its
residuals appear as (O-C)_2 in the table.

The complete light curves of YZ Phe defined by the individual observations are
shown in Figure 1 as intensity versus phase, overlaid with a preliminary light
curve solution (solid line).  An early analysis by DT indicates that YZ Phe is
a W-type W UMa system with a mass ratio of 0.41, a fill-out of 16% and a
component difference, delta T ~380 K.  A large 46deg radius single "dark spot"
was simultaneously modeled on the cooler component with a temperature factor of
only 0.96.  The preliminary reductions and analyses were done by MBA for his
undergraduate research project at Butler University.



                          Marcelo B. ARRUDA
                          J. I. Holcomb Observatory
                          Butler University
                          Indianapolis, IN 46208
                          USA

                          Ronald G. SAMEC ^a,b
                          Dept. of Physics and Astronomy
                          Millikin University
                          Decatur, Illinois 62522
                          USA
                          and
                          J. I. Holcomb Observatory
                          Butler University
                          Indianapolis, IN 46208
                          USA

                          Dirk TERRELL
                          Department of Astronomy
                          University of Florida
                          Gainesville, FL 32611
                          USA

a Visiting Astronomer, Cerro Tololo InterAmerican Observatory, National Optical
Observatories, which are operated by the Association of Universities for
Research in Astronomy, Inc.  under contract with the National Science
Foundation.

b This research was partially supported by a grant from NASA administered by
the American Astronomical Society.

References:

Gessner, H. & Meinunger, I., 1975, VSS, 8(5), 249
Hoffmeister, C., 1963, VSS, 6(1), 53
Jones, J., 1989, IBVS, No. 3296
Kilkenny, D. & Marang, F., 1990, IBVS, No. 3438