COMMISSION 27 AND 42 OF THE IAU
                   INFORMATION BULLETIN ON VARIABLE STARS
                               Number 3830

                                                         Konkoly Observatory
                                                         Budapest
                                                         18 January 1993

                                                         HU ISSN 0374 - 0676


                     HD28665: A PROBABLE DELTA SCUTI STAR


In this note we present the results of 1.9 hours of differential photometry of
HD28665. This bright (V=7.7) southern (declination -29 deg) star is classified
spectroscopically as F2III by Houk (1982). HD29507 (V=8.2, A2) and HD27905
(V=7.8, G0) were used as comparison stars.
   The observations were obtained using the Modular photometer attached to the
0.5 meter telescope of the South African Astronomical Observatory at
Sutherland. One cycle of observations consisted of Johnson V and B
measurements (two 30 second integrations per filter) of HD29507, HD28665 and
HD29507. Sky brightness measurements were obtained on average every 10
minutes. After correction of the count rates for sky background and
atmospheric extinction, the two comparison stars showed a common drift of about
0.03 magnitudes in V, which may be ascribed to sky transparency changes. The
B-V colour indices did not change by more than 0.005 during the period of
observation.


                              [FIGURE 1]


   The differential V measurements of HD28665 are shown in the upper panel of
the figure. Observations have been corrected for the zero-point drift, and
are given with respect to the average of HD29507 and HD27905 brightnesses. The
values shown can be related to V(HD27905) by subtracting 0.186, or to
V(HD29705) by adding 0.186. It is clear that the plotted sinusoid with a
frequency of 15.136 cycles/day (period 1.58 hours) and semi-amplitude of 0.049
magnitudes, fits the data extremely well. The lower panel shows the variation
in B-V, for which no differential correction was deemed necessary. The slight
phase difference found between the two fitted curves is not significant,
being about one standard error of the colour curve phase.
   The amplitude and period of the variation, together with the spectral type
of the star, are consistent with HD28665 being a delta Scuti pulsator.


                                  C. Koen & G. Roberts
                                  South African Astronomical Observatory
                                  P.O. Box 9
                                  Observatory
                                  7935
                                  South Africa



REFERENCE

Houk, N., 1982. Michigan, Catalogue of Two-Dimensional Spectral Types for the
     HD Stars. Volume 3., Department of Astronomy, University of Michigan. [BIBCODE 1982mcts.book.....H ]