A spectroscopic study of the peculiar stars in the open cluster NGC 2516.

Summary. Coude' spectrograms with a dispersion of 20 A/mm were taken for 22 stars in the open cluster NGC 2516 which is known to contain three red giants and several stars with peculiar spectra. The red giants are confirmed to be members of the cluster from measurement of their radial velocities and examination of their proper motions. Three new peculiar B- and A-type stars of the Si and the Ti-Si groups as well as a second B-emission line star were detected in the cluster. Thus, a total of nine stars in the cluster show strong peculiarities in their spectra among 39 early- type stars for which coude' spectra were so far obtained. Six of them belong to the Si or Ti-Si groups. The most interesting spectrum is that of the A0p (Ti-Si) star HD 66318 which shows the Sill 4128/4131 A doublet lines with equivalent widths exceeding 0.8 A. In the spectra of six stars, the Hg II 3984 A line is distinctly present. Equivalent widths are given for a small number of strong lines for all peculiar stars in the cluster. The peculiar stars in NGC 2516 are located on the main sequence with absolute visual magnitudes between - 1W8 <Mv < + 1 5. Arguments are presented suggesting that the silicon stars in NGC 2516 were formed by accretion onto their surfaces of silicon-rich matter lost from red giant stars which once were their companions in widely separated binary systems. This interpretation of the silicon stars leads to the conclusion that stars with masses of about 5-9 solar masses, after the red-giant stage, usually do not end their evolution by supernova explosions, but by becoming white dwarfs after relatively slow mass loss. Key words: open clusters - peculiar stars