COMMISSION 27 OF THE I. A. U.
        INFORMATION BULLETIN ON VARIABLE STARS
                    Number 2007

                                 Konkoly Observatory
                                 Budapest
                                 1981 August 27

                                 HU ISSN 0374-0676



    V 68 IN THE GLOBULAR CLUSTER M 3 (NGC 5272) IS A DOUBLE
              MODE RR LYRAE TYPE STAR


   We failed to confirm Szeidl's (1965) 10.9 day Blazhko effect
period of V 68 in M 3 by our 437 observations based on Moscow
collection of plates. These observations show sometimes the full
variation of amplitude of the star from night to night. We have
tested these observations on double mode pulsation using the 
theoretical suggestion by Christy (1966) that the beat period in
this case is equal to four first overtone periods. This test gave
positive result and only small correction was made to obtain the
precise beat period Pi= 1.395426d. Final value of the fundamental
period P_F was obtained from the formula:

             (1/P_F) = (1/P_H) - (1/Pi)

where P_H = 0.3559732d - the first overtone period derived by
Szeidl (1965).
   We represent our observations in Figure 1 like it was made
by Stobie (1970) and Efremov and Kholopov (1975) for double mode
cepheids VX Pup and V 367 Sct. The upper light curve in Figure 1
is constructed with elements by Szeidl the initial J.D. moment
of which is corrected:

   Max. J.D. hel. - 2425000.189 + 0.3559732d*E

The deviations from mean light curve excluding several points
are well represented by the following elements:

   Max. J.D. hel. - 2435602.441 + 0.4778805d*E

The middle light curve in Figure 1 is the "pure" curve for 
fundamental mode oscillation. The less dispersed "pure" first 
overtone light curve can be obtained by subtracting the mean 
deviation light curve from original observations. The lower light.
curve in Figure 1 represents our observations with elements by
Szeidl excluding fundamental mean periodic variation. Scattering
of light curves shows that the oscillations are not additive in
the observed light curve but suppress one another and have lower
amplitudes in anti-phase.

                         [FIGURE 1]
                         [FIGURE 2]

   Amplitudes of oscillations are 0.42m B in the fundamental and
0.45m B in the first overtone.
   To determine the location of the star in the instability strip
we have used P,V observations by Roberts and Sandage (1955) and
their relation with B,V magnitudes by Sandage (1959). The following 
colour indices were obtained: P-V = 0.08 and B - V = 0.27. This
puts the star just on the boundary between fundamental and first
overtone regions. The regions in M 3 occupied by variable stars
oscillating in different modes do not overlap (Figure 2). The
first overtone periods of RRc stars were transformed in Figure 2
to fundamental ones using the formula P_F = 1.340P_H to remove the
gap between first overtone and fundamental pulsators in the 
diagram.



                          V.P. GORANSKIJ

                          Sternberg State Astronomical
                          Institute
                          Moscow University, USSR


References:
Christy, R.P. 1966, Ap.J., 144, 108. [BIBCODE 1966ApJ...144..108C ]
Efremov, Yu.N., Kholopov, P.N. 1975, Variable Stars, 20, 133. [BIBCODE 1975PZ.....20..133E ]
Roberts, M., Sandage, A. 1955, A.J., 60, 185. [BIBCODE 1955AJ.....60..185R ]
Sandage, A. 1959, Ap.J., 129, 596. [BIBCODE 1959ApJ...129..596S ]
Stobie, R.S. 1970, Observatory, 90, 20. [BIBCODE 1970Obs....90...20S ]
Szeidl, B. 1965, Mitt. Sternw. ung. Akad. Wiss., Nr. 58, Budapest [BIBCODE 1965CoKon..58....1S ]
						[CoKon No. 58]