Optical spectroscopy of very low mass stars in the Pleiades

Optical spectrophotometry for several very low mass cool stars in the Palomar Pleiades has been obtained. The optical spectra of the PP stars has been compared with the optical spectra of a nearby field star sample, indicating that all of the PPl stars are dwarfs and that the faintest star is one of the coolest dwarf stars known; this star is very similar to VB 10 in its spectroscopic properties, but with a bolometric luminosity that is 1.5 mag brighter. The other PPl stars have spectral characteristics approximately similar to Gl 905. The Balmer emission found in all observed PPl stars is far less than those of the nearby cool stars. The possible brown-dwarf nature of PPl is tied to peculiarities concerning the theoretical models and to the presumed age of PPl. It is suggested that PPl is cooler than G1 406 and is similar to VB 10 according to most spectroscopic comparisons made. Several molecular TiO band indices were defined for effective temperature discriminants greater than 2400 K. The indicator of effective temperature, known as the PC index, is one based upon the slope between two low blanketing flux-density minima.