COMMISSION 27 OF THE I. A. U.
            INFORMATION BULLETIN ON VARIABLE STARS
                         Number 3622

                                             Konkoly Observatory
                                             Budapest
                                             10 June 1991

                                             HU ISSN 0374 - 0676


 G327 - A NEW HORIZONTAL BRANCH VARIABLE STAR BLUEWARD OF THE RR LYRAE
                           GAP IN M4


G327 (Greenstein 1939) = A64 (Alcaino 1975) = L3315 (Lee 1977) is a horizontal
branch star blueward of the RR Lyrae instability strip in the globular cluster
M4 (see Fig. 1). The proper motion study (Cudworth 1990 ) shows that G327 is a
cluster member (Pc=0.99). The magnitudes and colors of this star given by
different authors are:

   V=13.29, B-V=0.35 (Alcaino 1975)
     13.23,     0.43 (Lee 1977)
     13.24,     0.47 (Cudworth 1990)

We have pointed out the variability of G327 long ago(1979). Due to the low
accuracy of the photographic photometry and the unfavourable observation
conditions in China, we failed to find out its period. Thanks to the use of
the CCD camera, the preliminary periods have now been obtained. The
observations were made with the coated GEC CCD #2 attached to the Cassegrain
focus of the 60-cm reflector at the Mount Stromlo and Siding Spring Observatory
on 20 and 21 July 1990. The detector contains 383 X 577 useful pixels at a
scale of about 0.42"/pixel, thus covering a ~2.5' X 4' field. A total of 64
frames (60 visual, 4 blue) were obtained with the exposure time of 5 minutes,
and the seeing was between 2.1" and 3.5" (FWHM). Because no guiding device
can be used at the 60-cm reflector during exposing, 3 frames must be discarded
due to the much elongated images.

Some of the data were reduced at the Anglo-Australian Observatory with the micro
Vax 3800 and the others at the Nanjing University in China with the Sun 4
workstation. Only the aperture photometry routine of the DAOPHOT (Stetson
1987) was used to reduce the data because it is not a crowded star field. G298
(V=12.68, B-V=0.59) was used as the comparison star. Comparing with the star
G300 it is shown that the constancy of G298 is better than +-0.005 mag.
Scargle's (1982) modified periodogram was used to analyse the unevenly sampled
data because it can detect even faint signals in noisy (low signal to noise
ratio) data. The frequency interval to be searched was from 0.8 to 26. After
the data were prewhitened with the previous frequency, the same procedure was
run again. Three frequencies were thus found and Breger's (1991) program
PERIOD was used to improve the values of the frequencies found above
simultaneously. The results so obtained are:

     m(t) = ZEROPOINT + Summa i=1 to 3 (   a_i sin (2 pi t/p_i + 2 pi phi_i))


Here P1=0.3435d,  a1=0.01030,  phi1=0.1586,
     P2=0.1101,   a2=0.00606,  phi2=0.0942,
     P3=0.0550,   a3=0.00577,  phi3=0.3398,
ZEROPOINT = 0.643


                               [FIGURE 1]
                               [FIGURE 2]
                               [FIGURE 3]
                               [FIGURE 4]


The folded light curves are given in Fig. 2,3 and 4. Each light curve is
plotted with the data prewhitened with the other two frequencies. G327 is the
third horizontal branch variable star in M4 which is located blueward of the RR
Lyrae gap and checked with the CCD photometry by us (Yao 1987). Is it possible
that G327 pulsates both in the first overtone and second-overtone?

However, P1=0.5158d seems to fit the observations too because the data are
limited. Obviously, further observations are needed to determine the periods
accurately.

I wish to thank Prof. A.W. Rodgers, the director of MSSSO, for allocating the
telescope time. I thank also the staff members of MSSSO for help with
observing. I thank the staffs of AAO for using the computers. This work was
supported in part by the grant from the Chinese National Science Foundation.


                     YAO BAO-AN
                     Shanghai Observatory

References:

Alcaino, G., 1975, Astro. & Astrophys. Supp., 21, 1 [BIBCODE 1975A&AS...21....5A ]
Breger, M., 1991, Delta Scuti Star Newsletter, issue 3
Cudworth, K.M., 1990, A.J., 99, 1491 [BIBCODE 1990AJ.....99.1491C ]
Greenstein, J.L., 1939, Ap.J., 90, 387 [BIBCODE 1939ApJ....90..387G ]
Lee, S.W., 1977, Astro. & Astrophys., Supp., 27,367 [BIBCODE 1977A&AS...27..367L ]
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 ]
Yao Bao-an, 1979, Publ. of the Beijing Astro. Obs., No. 4, 1
Yao Bao-an, 1987, ESO Messenger, No. 50, 33 [BIBCODE 1987Msngr..50...33Y ]