COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                      NUMBER 356

                                  Konkoly Observatory
                                  Budapest
                                  1969 June 26


       ON A POSSIBLE METHOD OF IDENTIFICATION
               OF CEPHEID TYPES

      The investigation of brightness-colour relation of
variables of different types is carried out at the Main
Astronomical Observatory of the Ukrainian Academy of
Sciences.
      The results of a great number of photoelectric 
observations of cepheids (RR Lyr, CW and Cdelta types) in the
U, B, V system are analized. The basic series of observation
used in the present investigation are given in 1-7.
      The diagrams V versus B and U have been plotted
and these dependences for all the stars under investigation
proved to be linear. The values of DeltaV/DeltaB and DeltaU/DeltaB
have been obtained. They are denoted by Delta_V and Delta_U respectively.
These values were found to be different for different
types of cepheids:
  
                 Delta_V              Delta_U

       RR       0.77+/-0.03      0.96+/-0.06 
       CW       0.71+/-0.03      1.13+/-0.05     Mean error of Delta_V,U
       Cdelta   0.66+/-0.02      1.31+/-0.08     is +/- 0.02

      The diagram Delta_V versus Delta_U have been plotted (Fig.1)
where points correspond to the RR Lyrae stars, circles to
the CW stars and crosses to the C delta stars. The dependence
between Delta_V and Delta_U is:

                  Delta_U = 3.39 - 3.16 Delta_V

      Thus the result obtained shows that type of cepheid
can be identified through photoelectric U, B, V observations
without determining its light curves and periods.
      For instance BK Aur, TW CMa, U and X Vul have the
values Delta_V and Delta_U adequate to classical cepheids and SZ Tau
to CW stars (in the General Catalogue (8) the type of these
stars is not identified). W Vir differs from other stars
of that type. Its place on a Delta_V-Delta_U plane is far away from
CW stars.
      In addition the connection between Delta_U and metal
content (DeltaS) for RR Lyrae stars and between Delta_U and period
for C delta stars have been found (Fig.2 and Fig.3).

           		[FIGURE 1]
           		[FIGURE 2]
           		[FIGURE 3]
 
References:

1. W. Fitch et al., Lun. and plan. lab. comm. 5, pt. 2, 1966 [BIBCODE 1966CoLPL...5....3F ]
2. C. Sturch, ApJ 143, 744, 1966 [BIBCODE 1966ApJ...143..774S ]
3. R. Mitchell et al., Tonantzintla Bull. 3, no 24, 1964 [BIBCODE 1964BOTT....3..153M ]
4. K. Kwee, L. Braun, BAN Suppl. 2, 3, 1967 [BIBCODE 1967BANS....2...77K ]
5. W. Wisnievski, H. Johnson, Lun. and plan. lab. comm. 7,
  	pt. 2, 1968 [BIBCODE 1968CoLPL...7...57W ]
6. A. Michalowska-Smak, J. Smak, AA 15, 333, 1965 [BIBCODE 1965AcA....15..333M ]
7. P. Th. Oosterhoff, BAN XV, 199, 1960 [BIBCODE 1960BAN....15..199O ]
8. B.V. Kukarkin et al., General Catalogue of Variable
  	Stars, vol. 1, ed. 2, Moscow, 1958.




                       E. S. KHEYLO

               Main Astronomical Observatory of
              the Ukrainian Academy of Sciences