COMMISSION 27 OF THE I. A. U.
                 INFORMATION BULLETIN ON VARIABLE STARS
                              Number 2288

                                                      Konkoly Observatory
                                                      Budapest
                                                      1983 March 3

                                                      HU ISSN 0374-0676
 
            HR8768 - AN ULTRA SHORT PERIOD VARIABLE?

 An earlier investigation (by Balona 1982) of three of Jakate's
(1979) proposed early-type ultra-short-period variables cast doubt on
the existence of this group of variables. Balona saw no variation over
a few thousandths of a magnitude for HR3467, HR3582 and HR5294. This
led us to reinvestigate the remaining northerly member of the group
HR8768 (=HD217811=SAO 52626=BD +43deg4378). Percy (1980) has reobserved
this star, but in light of Balona's findings we decided to look one more
time.
   The variable was measured using SAO 52551 as a comparison and SAO
52599 as a check. Delta magnitude, in the sense HR8768-minus comparison,
is plotted versus heliocentric Julian Date in Figure 1. There seems to

                               [FIGURE 1]




be no significant variation in HR8768 on JD 2445235 and JD 2445269.
However, a gradual decline of approximately .02 magnitudes is present
from JD2445279.62-.75. Since the check star also drops in this time
period it is uncertain whether this can definitely be attributed to
HR8768. In any case, no ultra-short period variation such as that found
by Jakate (P=0.02d, Deltam=0.025mag) was found. To confirm this, we conducted a
periodogram analysis on our data for frequencies up to 100 cycles/day.
None were found with amplitude greater than 0.003mag, which is below the
estimated measurement error.
   The delta magnitude in B of SAO 52599 minus SAO 52551 is plotted
in Figure 2. SAO 52599 seems to have more variation than HR8768,


                            [FIGURE 2]


dropping 0.02mag on both JD 2945235 and JD 2445279. There may even be some
variation on JD 2445269 but this night was not as good as the other two.
Careful scrutiny of the data indicates the variation can be attributed to
SAO 52599 and not the comparison star SAO 52551. SAO 52599's spectral
type, A3, the magnitude of the variation (0.02mag), and the time-scale (2-5
hours) suggest that it might be a delta-Scuti variable but additional
data is needed to confirm its type of variability.



   In conclusion, it is always difficult to prove the photometric
constancy of a star, particularly a low amplitude variable, with only a
few nights data. However, on the basis of our observations of HR8768
we must support Balona's conclusion that Jakate's four stars are not
members of a new group of early-type ultra-short-period variables. It
will require further observations to determine if HR8768 has a low
amplitude variation that is either aperiodic or of long period.





                   J. S. SHAW, D. A. FRAQUELLI,
                   D. H. MARTINS and S. B. ANDREW
                   University of Georgia Observatory
                   University of Georgia
                   Athens, Georgia 30602



References:


Balona, L. A. 1982, IBVS No. 2120.
Jakate, S. M. 1979, Astron. J. 84, 1042. [BIBCODE 1979AJ.....84.1042J ]
Percy, J. R. 1980, IBVS No. 1734.