COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                     Number 1957

                                     Konkoly Observatory
                                     Budapest
                                     1981 April 21

                                     HU ISSN 0374-0676



          VARIABLE STARS IN THE PLEIADES CLUSTER


From October 22 till November 27, 1980, we performed photometry on 8 late
G and early K type stars in the Pleiades cluster. From previous measurements
on these type of stars in this cluster it looked as if many of them are
variable. The 8 stars, which were measured with the Walraven photometer on the
Dutch 91 cm telescope (Lub, 1979) on La Silla, ESO, form a random choice of
G and K type stars in the cluster. All of these stars are members according to
their proper motions and distance moduli. The selected stars are given in
Table I The numbers are from Hertzsprung (1947).
All of these 8 stars turned out to be variable according to our measurements
and for 5 of them a lightcurve was obtained. Also two of the comparison
stars are variable, but for only one of them a light curve could be obtained.
The light curves and the periods are given in Figures 1a and 1b as differences,
in 10log(I) for the V-channel, between the given star and substandard for the
cluster, star 804. The zero points for the phase calculations were JD=2444534.5
for star 34 and JD=2444542.5 for all others.



Table I


 Invest. stars  Comp. stars  local standard
  Hz   m_v      Hz      m_v   Hz   m_v
                               
 746   11.28    745    9.45   804  7.84
 129   11.4S    164    9.53
1220   11.83   1132    9.43
  34   12.04     25    9.47
1124   12.30   1122    9.29
1883   12.57   1797   10.10
 879   12.81    727    9.27
 686   13.35    745    9.45


                             [FIGURE 1a]
                             [FIGURE 1b]

                              [FIGURE 2]

Star 1883 shows clearly a BY Draconis lightcurve but has a rather short period
for this type of star. Like most of the BY Draconis stars this star is a flare
star (Haro et al, 1973). The light curve is stable within 0.003 magnitudes
in the V band, which, together with the short period, rules out the possibility
of rotational variation. Variations like described by Hartmann and Rosner (1979)
in the form of modifications of the convective energy transport seem much
more likely.
Star 686 is also known as a flare star (Haro et al, 1966, 1972). The period
of star 686 is not certain; a period of 1.98 days seems also possible, for
which the amplitude would probably be larger. For star 879 two periods are
given, of which the shorter one seems more likely. Star 1124 showed a minimum
which was getting deeper during our observing period. The period for star 34
was difficult to obtain because of the rather bad coverage of the light curve.
The stars 686, 879, 1124 and 34 are possibly also BY Draconis stars. Star
727 seems a regular variable star, but the light curve and thus the type
are still uncertain. No light curve could be obtained for star 1797.
For all of these stars and for star 804 search maps are given in Figure 2.
The diameter of each field is 12', the magnitudes indicated are photographic
magnitudes and the limiting magnitude is around m_v =13.5
                             

A paper on star 1883 together with Dr. M. Walker of Lick Observatory, who did
radial velocity measurements on this star, is in preparation.




                      P. ALPHENAAR and F. van LEEUWEN,
                         Sterrewacht,
                         Postbus 9513
                         2300 RA Leiden
                         Nederland



References:
Haro, G. and Chavira, E., Vistas in Astronomy, 8, 96 (1966) [BIBCODE 1966VA......8...89H ]
Haro, G. and Chavira, E., Bol. Ton. y Tac. 6, 155 (1972) [BIBCODE 1972BOTT....6..155H ]
Haro, G. and Chavira, E. and Gonzalez, G. Bol. Ton. y Tac. 1, 3 (1973) [BIBCODE 1973BITon...1....3H ]
Hartmann,L. and Rosner, R. Ap. J. 230, 802 (1979) [BIBCODE 1979ApJ...230..802H ]
Hertzsprung, E., Leiden Annalen, XIX, part A (1947) [BIBCODE 1947AnLei..19A...1H ]
Lub, J, ESO Messenger no 19, 1, (1979) [BIBCODE 1979Msngr..19....1L ]