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 a nd possible Tucana members. The implied age of the Tucana association stars , less than or similar to 40 Myr, is consistent with the age determined fro m a previous analysis by Stelzer & Neuhauser of the X-ray luminosities of p lausible association members. Based primarily on space motions and X-ray fl uxes, we identify potential new members of the Tucana association not consi dered in earlier studies. Torres and coworkers recently identified a group of post-T Tauri stars, the Horologium association, which is located near th e Tucana association in right ascension and declination. Because the Horolo gium stars have the same space motions, age, distance from Earth, volume de nsity, 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 stre am.