COMMISSION 27 AND 42 OF THE IAU
                   INFORMATION BULLETIN ON VARIABLE STARS
                               Number 3826

                                                         Konkoly Observatory
                                                         Budapest
                                                         11 January 1993

                                                         HU ISSN 0374 - 0676


              POSSIBLE VARIABILITY OF PLEIADES MEMBER HII 263

   We report here the observation of anomalous dimming seen in relative photometry
of the Pleiades cluster member HII 263. As part of a program to monitor
young stars in open clusters to derive rotation periods from the observed light
variations due to starspots (Prosser et al. 1993), the Pleiades cluster
member HII 263 was monitored at the Whipple Observatory 48-inch telescope at
Mt. Hopkins, Arizona during late October, early November 1992 (Julian dates:
2448922-2448933). CCD photometry of the field containing HII 263 enabled
relative V magnitudes between HII 263 and comparison stars of similar
brightness to be obtained from each CCD frame. The data will be discussed more
fully in a future paper along with the analysis of other stars.
   HII 263 is located at RA=03h41m6.3s, DEC=+24d7'8" (1950), has V=~11.6,
spectral type G8 (Soderblom et al. 1992a) and an observed v sin i of 10 km/sec
(Soderblom et al. 1992b). With such a low v sin i, one would predict that
HII 263 would possibly have a variability with a period of several days and an
amplitude on the order of a few hundredths of a magnitude, similar to that
observed among Hyades members (Radick et al. 1987). While our data did not
reveal any low-amplitude systematic variations, an anomalous dimming of HII 263
was detected on the night of November 3, 1992 (UT)  The accompanying figure
plots the relative V magnitudes between HII 263 and each of the two comparison
stars (A and B) and the relative V magnitudes between the comparison stars over
time. The two comparison stars used are HII 309 (=A) and HII 239 (=B), both of
which are considered not to be Pleiades cluster members. The observed
fluctuation in HII 263 was ~0.04 mag, while no variation was detected in the
comparison stars. The relative photometry is believed to be accurate to about
±0.01 mag.  As only one event was observed, no periodicity information for HII
263 could be obtained. Systematic monitoring of HII 263 is recommended in
order to determine if the observed variation is periodic, possibly indicating
that HII 263 is an eclipsing binary system. If it is an eclipsing system, it
must either be a grazing eclipse or the companion must be much smaller than the
primary.


                               [FIGURE 1]



                                    Charles F. Prosser
                                    John R. Stauffer
                                    Center for Astrophysics
                                    60 Garden St. MS-66
                                    Cambridge, MA 02138 USA
                                    email: prosser@cfa0.harvard.edu
                                           stauffer@ cfa0.harvard.edu



References:

Prosser, C.F., Schild, R.E., Stauffer, J.R., and Jones, B.F. 1992, to appear in
     Publ. Astron. Soc. Pacific, March 1993.
Radick, R.R., Thompson, D.T., Lockwood, G.W., Duncan, D.K., and Baggett, W.E.
     1987, ApJ, 321, 459. [BIBCODE 1987ApJ...321..459R ]
Soderblom, D.R., Jones, B.F., Balachandran, S., Stauffer, J.R., Duncan, D.K.,
     Fedele, S., and Hudon, J.D. 1992a, "The Evolution of the Lithium
     Abundances of Solar-type Stars", preprint. [BIBCODE 1993AJ....106.1059S ]
Soderblom, D.R., Stauffer, J.R., Hudon, J.D., and Jones, B.F. 1992b, "Rotation
     and Chromospheric Emission among F, G, and K Dwarfs of the Pleiades",
     preprint. [BIBCODE 1993ApJS...85..315S ]