A CCD-BASED SEARCH FOR VERY-LOW MASS MEMBERS OF THE PLEIADES CLUSTER

We have obtained deep CCD V and I images of a number of fields near th e center of the Pleiades open cluster. We have also obtained imaging d ata for Praesepe, a very similar cluster in terms of distance and rich ness but nearly 10 times older than the Pleiades. Because brown dwarfs are predicted to become much fainter and cooler between Pleiades and Praesepe ages, this provides a powerful differential technique for pla cing constraints on the brown dwarf population in open clusters. Combi ned with our previously reported observations, we now have data for ab out 0.4 sq deg in the Pleiades, corresponding roughly to 5% of the are a of that cluster. We have searched the new CCD frames for additional Pleiades brown dwarf candidates. Two possible candidates are present, the faintest of which has V congruent-to 22.5, (V-I)K congruent-to 4.6 . Because we do not have proper motion data and the colors of these ob jects are not redder than the reddest known field stars, it is possibl e that some or all of our candidates are somewhat higher mass field st ars rather than Pleiades-age brown dwarfs. Even if all six of the prop osed brown dwarf candidates in our 0.4 sq deg field are Pleiades membe rs, the relatively small number found suggests that low mass stars or brown dwarfs do not contribute significantly to the total mass of the cluster.