Tucana association

Among star clusters, only the sparse Ursa Major nucleus is closer to Earth than the recently identified Tucana. association. Based on new photometric VRI magnitudes, we construct a color-magnitude diagram composed of likely and possible Tucana members. The implied age of the Tucana association stars, less than or similar to 40 Myr, is consistent with the age determined from a previous analysis by Stelzer & Neuhauser of the X-ray luminosities of plausible association members. Based primarily on space motions and X-ray fluxes, we identify potential new members of the Tucana association not considered in earlier studies. Torres and coworkers recently identified a group of post-T Tauri stars, the Horologium association, which is located near the Tucana association in right ascension and declination. Because the Horologium stars have the same space motions, age, distance from Earth, volume density, and range of spectral types as Tucana stars, we suggest that, rather than being characterized as a separate group, it would be appropriate and economical to subsume the Horologium association stars into the Tucana stream.