Bright-Line Stars among the Taurus Dark Clouds.

Abstract

On QbjeCtiVe-priSm photographs of three areas of the Taurus dark clouds, 40 faint stars with Ha emission were discovered. Slit spectrograms of 35 of these stars were examined for the purpose of finding spectral ,peculiarities which might be attributed to interaction between the stars and the surrounding clouds. Except for two stars of type Be which are probably not involved in the clouds and one peculiar A4e star, the stars are main-sequence stars of late spectral type and low luminosity. The stars are con- centrated in small regions in or near areas of great obscuration. If these stars are of normal luminosity and are at the distance of the clouds, their apparent magnitudes are generally too faint as a result of space absorption. The spectra show many of the characteristics previously found in the T Tauri variables. The hydrogen and Ca ii (H and K) bright lines are extremely strong in spectral types dGe-dM2.5e. Emission lines of He I, Fe I, Fe II, and [S ii] decrease in intensity in later spectral types in the two Taurus areas but are practic3lly absent in stars of the area in Orion. Related stars-A few stars with similar spectra, located in other regions of the sky are discussed for comparison with the Taurus stars. Radi~al velocities.-The approximate radial velocities from emission and absorption lines were meas- ured. The differences, emission minus absorption, seem to be greatest for the earlier types, which also show the strongest T Tauri characteristics