An emission sequence in pre-main-sequence flare stars

Optical spectra of quiescent pre-main-sequence flare stars in Orion are presented. The spectra cover ∼3600-4600 A at ∼3 A resolution, and were taken using an optical fibre fed spectrograph. The spectra reveal that most of the stars have Ca II H and K and the Balmer lines in emission, and approximate surface fluxes for these lines are deduced, along with Ca I absorption equivalent widths. The observed stars fall into four distinct types, according to the strength of the emission line sprectrum