COMMISSION 27 OF THE I. A. U.
        INFORMATION BULLETIN ON VARIABLE STARS
                     Number 1125

                                 Konkoly Observatory
                                 Budapest
                                 1976 April 12


          A STUDY OF THE PERIOD OF HR 6684



  The variability of HR 6684 (=HD 163472, alpha_1900=17h51.3m,delta_1900=
=+0d41', V=5.81, B2 IV-V) was discovered by Jerzykiewicz (1972,
Publ.Astron.Soc.Pacific 84, 718) whose observations indicated a
period of 0.13989d and an amplitude of 0.04 in b. The short period,
the small amplitude and the spectral type led Jerzykiewicz to suggest 
that HR 6684 is a beta Cephei (or beta Canis Majoris) type variable, 
although the derived period is quite short for this class of
stars. Observations by McNamara and Bills (1973, Publ.Astron.Soc.
Pacific 85, 632) seemed to confirm the variation of HR 6689 with
Jerzykiewicz's period, but this period did not satisfy their 
observations of the radial velocity made to test the classification
as a beta Cephei variable. The earlier radial velocity observations
by Feast, Thackery and Wesselink (1957, Mem.Roy.Astron.Soc. 68, 11)
and Petrie and Pearce (1961, Publ.Dominion Astrophys.Obs. 12, 1) 
also seemed to have the same problem. These facts combined with the
rather short period suggest that the period found by Jerzykiewicz
might be spurious, a common accurance with short period variables
observed for less then a complete cycle. New photometric and 
radial velocity observations by Morton and Hansen (1974, Publ.Astron.
Soc.Pacific 86, 943), Bolton, Percy, and Shemilt (1975, Publ.Astron.
Soc.Pacific 87, 595) and Pike (1974, Publ.Astron.Soc.Pacific 86,
681) seemed to be satisfied by Jerzykiewicz's period but they did
not rule out the possibility of an alternative period since in each
case less than a full cycle of the variation was covered.
  In order to test if the period found by Jerzykiewicz is spurious 
a new period determination for HR 6684 has been carried out
using all available observations, both photometric and of radial
velocities. The method of Lafler and Kinman (1964, Astrophys.J.
Suppl. 9, 216) was used to search each set of observations for 
possible periods in the range 0.11-0.21 days. It was found that there
are two (but only two) periods in this range that satisfy all the
observations:
         P = 0.139889d;     1/P = 7.1485 d^-1
         P = 0.162723d;     1/P = 6.1454 d^-1

The first period is that previously accepted and the other the
period related with this by one in the reciprocal.
  The available observational material was insufficient for 
determining which of the two possibilities is the true period. An
attempt to decide the question by comparing the absolute magnitude 
implied from Hgamma, Hbeta, and Halpha photometry with the known period-
luminosity law for beta Cephei stars was also inconclusive but showed 
that whichever of the two is correct HR 6684 is most likely
pulsating in the first vibrational mode.
  Further photometric and radial velocity observations of
HR 6684 covering at least 5h are desired to clarify the question
of its period.


                         PATRICIA ROSENZWEIG
                         Facultad de Ciencias
                        Universidad de Los Andes
                          Merida, Venezuela





                  AMENDMENT

to the paper "Ultra-Violet Blazhko-Effect of X Ari" published in
                 IBVS No. 1097


  I have noticed some errors I made in Umax-magnitudes of X Ari
on the second page of my paper, however, all conclusions remain
unchanged. The correct magnitudes should be:
  JD 2438017 - 9.45 mag, 2437918 - 9.50, 2437976 - 9.49,
  2437916 - 9.50, 2438010 - 9.46, 2437945 - 9.48 (in order of
the text).


                         M. S. FROLOV