COMMISSION 27 OF THE I. A. U.
        INFORMATION BULLETIN ON VARIABLE STARS
                    Number 3431

                                   Konkoly Observatory
                                   Budapest
                                   8 February 1990

                                   HU ISSN 0374 - 0676




   K1040 - A NEW 4.3 HOUR RED GIANT VARIABLE STAR IN M15

  It has been reported that G512, a star located at the top of the red
giant branch of the C-M diagram in the globular cluster M4, has light
variation with a quasi period of about 66 minutes (Yao Bao-an et al.
1981). We believe that the short-period variation is a common
phenomenon among this kind of stars, so other globular clusters are
being searched for.
  Here we report the variation of another similar star K1040 (Küstner
1921) = S6 (Sandage 1970) in the globular cluster M15.
  K1040 is located at the top of the red giant branch too (see Fig.1).
The magnitude and colors of this star given by Sandage are V=13.35,
B-V=1.21, U-B=0.84. The proper motion study (Cudworth 1976) shows that
K1040 is a cluster member (Pc=0.99).
  The star was observed by us with the RCA CCD at the Cassegrain focus
of the Zeiss 1-m reflector (f/13.3) at the Yunnan Observatory in
November 1988. This detector contains 320 X 512 pixels at a scale of
0.47"/pixel, thus covering a 2.5' X 4' field. Two series of 590-second
exposures taken in rapid succession over an interval of about 3.4 and
3.7 hours were obtained on 1988 November 12 and 15 (36 yellow, 4 blue).
The seeing was between 1.2" and 2.5" (FWHM). The red star K1073 was used
as the comparison scar, it is constant to at least < 0.01 mag by
comparing with other stars within the nights we observed. Because the
distance between K1040 and K1073 is only 67" and the difference of the
instrumental color index B-V between them is only 0.13 mag, so the
differential extinction correction can be neglected. The CCD frames
were reduced by DAOPHOT (Stetson 1987) in IRAF which is mounted in the
Vax 8350 computer of the Yunnan Observatory. Due to the fact that there
are several faint nearby stars around K1040, though they are 5
magnitudes fainter than K1040 in brightness, the CCD magnitudes of
K1040 are less accurate than that of K1073. The standard error of
V(K1073) - V(K1040) is about 0.006 mag.
 From the "real time " light curve it can be seen directly that the
star has a period value between 0.12 and 0.5 day. In addition, it may
have long-term period behavior because the mean magnitude of the star
on 12 November is fainter than that on 15 November by 0.014 mag.
However, aiming at the short-period variation, the zero point shift of
different nights was adjusted by adding a constant and the period was
searched for within the range 0.12 - 0.5 d.
  The folded light curve got by P=0.1787 day with the peak to peak
amplitude about 0.04 mag is given in Fig.2.
  Further observations are needed to monitor the possible long-term
variation.


                          [FIGURE 1]
                          [FIGURE 2]


  I thank Chen Fu-xiang for help with observing. I am indebted to Lou
En-rui for help with running IRAF.

                          YAO BAO-AN
                          Shanghai Observatory

References:

Cudworth, K., 1976, A.J., 81, 519 [BIBCODE 1976AJ.....81..519C ]
Kustner, F., 1921, Veroff. Sternw. Bonn, No. 15
Sandage, A.R., 1970, Ap.J., 162, 841 [BIBCODE 1970ApJ...162..841S ]
Stetson, P.B., 1987, P.A.S.P., 99, 191. [BIBCODE 1987PASP...99..191S ]
Yao Bao-an et al., 1981, Acta Astrophysica Sinica, 1, 311 [BIBCODE 1981AcApS...1..311Y ]