COMMISSION 27 OF THE I. A. U.
           INFORMATION BULLETIN ON VARIABLE STARS
                       Number 3461

                                         Konkoly Observatory
                                         Budapest
                                         14 May 1990

                                         HU ISSN 0374 - 0676

         UBVR PHOTOMETRY OF THE ZZ CETI STAR G185-32

    We observed the ZZ Ceti variable white dwarf star G185-32
(= GR277 = PG1935+276) during eight nights between 11 June 1989
end 31 July 1989, U.T. Our observations were made with the 24-
inch (0.6 m) Cassegrain telescope at Jet Propulsion Lab's Table
Mountain Observatory in the San Gabriel Mountains, near
Wrightwood, California, U.S.A. A light curve for this star was
constructed with the unfiltered measurements obtained from a
single-channel photometer containing a dry-ice cooled (-78degC) RCA
1P-21 photomultiplier tube. The measurements of U, B, V, and R
were made using the same photometer with a dry-ice cooled
Hamamatsu 943-02 photomultiplier tube. Each of our measurements
of program star, comparison stars, and sky brightness was made
with a ten-second integration. We used either a 16" or 20"
diameter aperture, depending on nightly seeing conditions.
    The extinction of a large sample of standard stars was
measured with the Hamamatsu 943-02 tube in early June of 1989.
From this data we calculated transformation coefficients to
convert our results to the Johnson magnitude scale, using the
methods outlined in Henden and Kaitchuck (1).
    A light curve for G185-32 was obtained in 1981 by McGraw, et
al. (2). Our curve is a composite obtained from data taken on
three nights of observing: 12 June; 10 July, and 11 July. Figure
(1) shows the difference in the magnitudes of G185-32 and
comparison star SAO 087458, plotted against an arbitrary time
scale. Figure (2) shows the difference in the magnitudes of SAO
087458 and our second comparison star, SAO 087405. The
fluctuations in the curve of Figure (1) are well above the noise
level determined by Figure (2).


                          [FIGURE 1]

 Figure 1 - Light curve for G185-32 from unfiltered measurements

                          [FIGURE 2]

 Figure 2 - System noise level from unfiltered measurements.


    Our light curve for G185-32 does not show substantial
differences from that of McGrew. Both the erratic 200-second
quasi-period and 0.02 to 0.05 magnitude change seen by McGrew are
apparent in Figure (1).
    Our first two nights of observing were dedicated to
obtaining accurate color magnitudes of G185-32. The values of U,
B, V, and R were calculated by averaging two sets of 16
continuous measurements of each color from each night. The
instrumental magnitudes were then transformed to the Johnson
system. The value of the experimental uncertainty is the
standard deviation of each set of 32 color measurements, carried
through our transformation equations.

    The colors of G185-32 are as follow:

                U = 13.26 +/- 0.23
                B = 13.50 +/- 0.10
                V = 13.21 +/- 0.03
                R = 13.18 +/- 0.10
             (U-B) = -0.24 +/- 0.13
             (B-V) = +0.29 +/- 0.07
             (V-R) = +0.03 +/- 0.07

    G185-32 was observed in 1967 by Eggen (3), as part of a
survey of 500 faint, blue stars. Our results show that this star
has become dimmer over the last 22 years. Eggen established a
value of V = 13.00 for G185-32; this is brighter by a factor of
approximately 1.2 than our measurements indicated. We also
notice that while our value for (B-V) does not show a significant
change, within our experimental uncertainty, from Eggen's value
of (B-V) = +0.17, our value for (U-B) shows a definite increase
from the 1967 value of (U-B) = -0.57. This would seem to
indicate that while the effective temperature of G185-32 has
remained relatively unchanged, there has been a change in the
structure of its outer atmosphere. Such an alteration in the
nondegenerate stellar exterior could also account for the
decreased brightness of this star.
    Because of the small amplitude and erratic behavior of the
light curve of G185-32, further observations are needed to
determine whether the changes in the color magnitudes have
affected the white dwarf's oscillation behavior.
    This research was supported by a grant from the Pew
 Foundation.


D. W. HOARD
Harvey Mudd College
Claremont, CA 91711
U.S.A

ELNA NAGASAKO
Pomona College
Claremont, CA 91711
U.S.A.

Dr. WILLIAM SANDMANN
Harvey Mudd College
Claremont, CA 91711
U.S.A.



REFERENCES:

(1) Henden, Arne A. and Kaitchuck Ronald H., Astronomical
  Photometry, Van Nostrand Reinhold Company, New York, 1982. [BIBCODE 1982asph.book.....H ]

(2) McGraw, John T., et.al., "Two New Variable White Dwarfs:
  G185-32 and G191-16", The Astrophysical Journal, vol.250,
  1 November 1981, pp.349-354. [BIBCODE 1981ApJ...250..349M ]

(3) Eggen, O.J., "Luminosities, Colors, Motions, and Distribution
  of Faint Blue Stars", The Astrophysical Journal
  Supplement, vol.16, 1968, p.97. [BIBCODE 1968ApJS...16...97E ]