COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                     Number 1734

                                    Konkoly Observatory
                                    Budapest
                                    1980 January 29


                THE VARIABILITY OF HR 8768


HR 8768 (HD 217811, B2V, m_v=6.38) is one of four members of a new class of
early-type ultra-short-period variables proposed by Jakate (1979). The other
three members are the southern stars HR 3467, HR 3582 and HR 5285. These stars
are all B2V and B3IV stars, with periods of 30-50 minutes, and ranges of about
0.02m in blue light.

Because of the small ranges of these stars, it is particularly important that
their variability be confirmed by other observers. Accordingly, HR 8768 was
observed on two good photometric nights with the #4 0.4 m telescope at the Kitt
Peak National Observatory in Arizona, U.S.A. The telescope was equipped with a
dry-ice-cooled 1P21 photomultiplier, and pulse-counting electronics. On the
first night, HR 8755 and HR 8806 were used as comparison stars. On the second
night, in order to improve the time resolution and accuracy, only HR 8806 was
used. The magnitude differences, corrected for differential extinction, are
shown in Figure 1. Approximate error bars are given for the data obtained on
the second night. The average accuracy of the magnitude differences is
+-0.002m, as determined from the internal scatter and from the scatter in
Delta b (HR 8806-HR 8755).

The variability of HR 8768 is only marginally apparent on the first night, but
is quite apparent on the second. The period is about 35 minutes (slightly
longer than Jakate's value of 28 minutes) and the range varies from 0.01m on
the first night to 0.02m on the second. Jakate found a range of 0.025m; the
range appears to be variable. Although Figure 1 appears to confirm the
ultra-short-period variability of HR 8768, independent confirmation of this and
other members of the class would be desirable.

                            [FIGURE 1]

This research was supported by the Natural Sciences and Engineering Research
Council of Canada. I thank the Kitt Peak National Observatory for the use of
the facilities there.


JOHN R. PERCY
Department of Astronomy,
University of Toronto,
Toronto, Canada
M5S 1A7

Reference:

Jakate, S.M. 1979, Astron. J. 84, 1042. [BIBCODE 1979AJ.....84.1042J ]