COMMISSION 27 OF THE I. A. U.
       INFORMATION BULLETIN ON VARIABLE STARS
                    Number 1073

                               Konkoly Observatory
                               Budapest
                               1975 December 1



 DOUBLE MODE CEPHEID V367 Sct IN OPEN CLUSTER NGC 6649


  Some years ago we found for V367 Sct the period 6.2930d and
suggested that the scatter on its light curve is caused by 
secondary period (1). The problem is very important because V367
Sct is the cepheid member of the open cluster NGC 6649 (2).
 Our conclusions were disputed by Tammann (3) who obtained
the period 5.118d and somewhat peculiar light curve and recently 
by Madore and van den Bergh (4) who found the period 5.2551d
rejecting a number of observations. However, both periods 
contradict to the 320 photographic observations of V367 Sct which
are at our disposal. The plates were obtained during JD 2418529-
42303.
  Using the photoelectric observations published in (2,3,4) we
have searched for secondary period of V367 Sct. Periodicity in
the set of residuals relative to a mean curve corresponding to
the period 6.2930d (Fig. 1a) was searched for, the computer 
programme X-3a (5) being used. In the interval 1.5d-10d only two 
possible periods, 4.3802d and 4.3849d, were found. It were the 
photographic observations that permitted to ascertain that the 
secondary period is 4.3849d. The period ratio 0.696 is close to that
for all beat cepheids and we believe that the period 6.2930d is
the fundamental one whereas the period 4.3849d corresponds to the
first overtone. The photoelectric light curves (Figs. 1b and 1c)
were derived by Stobie's iterative technique (6).
  The star has the longest period among double mode cepheids
and it is the only beat cepheid in open clusters. The membership 
of V367 Sct in a young cluster and its position in the
colour-magnitude diagram indicate that beat cepheids are
classical ones. The star is, however not essentially brighter
than cluster main sequence stars as cepheids usually do. The
Fig. 1 from (7) indicates the pulsational mass 2 - 2.5 in solar 
units whereas evolutionary mass of a six-day cepheid is
about 6 M_Sun, and the star conforms to period-luminosity and 
period-age relations for classical cepheids. There is probably 
something wrong in determinations of pulsation mass of beat cepheids.
  The membership of V367 Sct in a cluster implies the star is
a clue to the nature of beat cepheids and deserves exceptional
attention.

                   [FIGURE 1]


                          YU.N. EFREMOV
                           P.N. KHOLOPOV

                 Sternberg Astronomical Institute, Moscow.


 References:

 1. P.N. Kholopov, Yu.N. Efremov, Astr.Circ. 437, 1967
 2. C. Roslund, W. Pretorius, Lunds Med.Ser. 1, nr. 205, 1963 
 3. G.A. Tammann, Astr.& Ap. 3, 308, 1969 [BIBCODE 1969A&A.....3..308T ]
 4. B.F. Madore, S. van den Bergh, Ap.J. 197, 55, 1975  [BIBCODE 1975ApJ...197...55M ]
 5. P.N. Kholopov, Sternberg Astr.Inst.Publ. 40, 72, 1970 [BIBCODE 1970TrSht..40...72K ]
 6. R.S. Stobie, Obs. 90, 20, 1970 [BIBCODE 1970Obs....90...20S ]
 7. J.O. Petersen, Astr. & Ap. 27, 89, 1973 [BIBCODE 1973A&A....27...89P ]