COMMISSIONS 27 AND 42 OF THE IAU
             INFORMATION BULLETIN ON VARIABLE STARS
                         Number 3955

                                               Konkoly Observatory
                                               Budapest
                                               24 November 1993

                                               HU ISSN 0374 - 0676


            vZ1140 - A NEW UNUSUAL VARIABLE STAR IN M3


 vZ1140 (von Zeipel 1908)=II-54 (Sandage 1953) is nearly located at the intersection of
the horizontal branch and red giant branch in the C-M diagram of the globular cluster
M3 (see Figure 1). The star positions in second of arc relative to the cluster center are:
x=75, y=250. The magnitude and colors of this star are V=15.13, B-V=0.75, U-B=0.23
(Johnson and Sandage, 1956). According to Zhukov (1971), the proper motion of the star
belongs to Ebbighausen class 3, showing that it is a cluster member.
 Here we report the unusual light variation of II-54.
 The star was observed by Yao Bao-an and Chen Fu-xiang with the TH-7882 CCD at
the Cassegrain focus of the 2.16-meter reflector (f/9) at the Beijing Observatory in March
1993. This detector contains 576x384 pixels (pixel size 23x23 mum) at a scale 0.244"/pixel,
thus covering a 2.43` x 1.56` field. Four series of 300-second or 600-second exposures taken
in rapid succession over an interval of about 5.0, 4.2, 6.2 and 4.6 hours were obtained
on 1993 March 16, 17, 18 and 19 (90 yellow, 5 blue). The seeing was between: 1.3' and
3.2' (FWHM). After deleting 6 poorly guided exposures, 84 yellow CCD frames were
used to analyse the light variation. The star AO (V=14.70, B-V=0.72) (Johnson and
Sandage, 1956) was used as the comparison star. It is constant to at least within 0.01.
mag by comparing with other stars during the nights we observed. Because the distance
between II-54 and AO is only 83.6" and the difference of B-V is only 0.03, as well as the
observations were obtained with the air mass less than 1.3, so the differential extinction
correction can be neglected. The CCD frames were reduced by DAOPHOT (Stetson,
1987) in IRAF which is mounted in the Sun 4/65 workstation of Shanghai Observatory.
Only the aperture photometry was used because it is not a crowded star field for these
stars. Scargle's (1982) modified periodogram was used to analyse the unevenly sampled
data. A frequency nu_1~=2.93 was searched out with extremely low false 
alarm probability.
After prewhitened with nu_1, the above procedure was repeated again in 
order to search for
other possible period and a closely spaced frequency nu_2~=2.62 was found 
with low false
alarm probability too. Then Breger's (1991) program PERIOD was used to run nonlinear
least squares fitting to improve the values of the frequencies found above simultaneously.
 The results so obtained are:
                     
          m(t) = Zeropoint + Summa_i=1 to 2 * a_i*sin(2pi*t/p_i + 2pi*phi_1)
                     
         Here    P_1=0.35165d, a_1=0.04808, phi_1=0.4187,
                 P_2=0.35840d, a_2=0.04054, phi_2=0.2049,
         Zeropoint=0.476

                            [FIGURE 1]
                            [FIGURE 2]
                            [FIGURE 3]
                            [FIGURE 4]
                            [FIGURE 5]
                            [FIGURE 6]
                            [FIGURE 7]

  The zeropoint 0.476 represents the mean magnitude difference between II-54 and AO.
The folded light curves are given in Figures 2 and 3. Each light curve is plotted with the
data prewhitened with the other frequency.
  Here the squares refer to observations on 1993 March 16, the circles on March 17, the
X's on March 18 and the triangles on March 19. The "real time" light curves are given
in Figures 4, 5, 6 and 7 where the continuous curves represent the calculated ones using
the formula given above. Time refers to the heliocentric Julian date.
  We note that the scatter in the folded light curves in Figures 2 and 3 can be reduced if
a third frequency nu_3=3.269 is included with an amplitude of about 0.005 mag. However,
a nu_3=6.547 seems to fit the observations too, so we will not include nu_3 into the calculation
until more observations are obtained. Obviously, further observations are urged.
  This work was supported in part by the grant from the Chinese National Science
Foundation.


                          YAO BAO-AN
                          ULOA/CAS
                          Shanghai Observatory
                          China

                          ZHANG CHUN-SHENG and QIN DAO
                          Purple Mountain Observatory
                          China



References:

Breger, M., 1991, Delta Scuti Star Newsletter, No. 3
Johnson, H. L., and Sandage, A. R., 1956, Ap. J., 124, 379 [BIBCODE 1956ApJ...124..379J ]
Sandage, A. R., 1953, A. J., 58, 61 [BIBCODE 1953AJ.....58...61S ]
Scargle, J. D., 1982, Ap. J, 263, 835 [BIBCODE 1982ApJ...263..835S ]
Stetson, P. B., 1987, P.A.S.P., 99, 191 [BIBCODE 1987PASP...99..191S ]
von Zeipel, M. H., 1908, Ann. Obs. Paris, 25 F1 [BIBCODE 1908AnPar..25F...1V ]
Zhukov, L. V., 1971, Trudy Pulkova Obs., Ser. 2, 78, 160 [BIBCODE 1971TrPul..78..160Z ]