Pre-Main-Sequence Stars in the Pleiades Supercluster

The Pleiades supercluster, which contains the eponymous cluster as well as the α Persei cluster, is a well defined association of both cluster and noncluster stars with ages in the range from 2 × 106 yr (1.5 mag above the Hyades main sequence) to 5 × 107 yr (1 mag above the Hyades main sequence) and 1.25 × 108 yr (main sequence). The pre-main sequence stars are in the dark clouds of Lup, Sco, and CrA, as well as on the fringes of the Taurus cloud, but some are not obviously associated with any dark clouds. The most interesting PMS objects may be the components of the system of HD 155555 (V834 Am), in which the A component is similar to the spotted, PMS star PZ Tel, B is similar to the PMS star AB Dor, and C is nearly identical to the M-type PMS star Ti 8 in the Pleiades cluster. Another interesting supercluster member is the possible PMS eclipsing binary HR 8323 (δ Cap), an extreme ultraviolet and x-ray source. Several of the supercluster members are visual binaries with high orbital eccentricity and the masses derived from the cluster parallax for those with trustworthy orbital elements agree well with the model predictions. Attention is called to the close binary HD 102077, consisting of a pair of spotted dwarf stars (V 838 Cen), which are main sequence stars as are, surprisingly, the components of AK Sco, if they are also candidate supercluster members. Nearly two dozen of the candidate members are within 40 pc of the Sun and two of these, HR 5463 (α Cir) and HR 5897 (β TrA), may be undetected binaries.