Spectral properties of luminous late-type stars.

A survey is given of some spectral characteristics observed from a material of 16 A/mm plates covering the visual-red spectral region of 52 luminous stars of spectral classes KO to M7. Of these stars 11 are of luminosity class III and 41 of class II or I, including 17 supergiants belonging to the I Per association. New spectral types are given for 13 stars. The D line profiles are examined in Section 3. Strong interstellar components are found to be present in several stars. The stars RW Cep and HR 8248 show evidence of strong circumstellar components. The Ha line is discussed in Section 4, where it is found that the supergiants exhibit various degrees of, mainly, violet- displaced emission. Th these stars the total width of Ha at half intensity points decreases statistically with increasing violet-displaced emission. The interferring emission disturbs the relation between Ha absorption and luminosity found for late-type stars. Several stars show evidence of time-variations in Ha. In BD + 56 595 a strong flare-like event is observed. Th Section 5 the Li abundances are determined. There is some indication that the highest Li abundances are found in stars which show evidence of peculiar circumstellar activity. The supergiants show Li in the range observed for the giants. One K supergiant, HR 8248, indicates an unusually high Li content. Several I Per supergiants show high Li abundances, three of the central stars being conspicuous. It is found in Section 6 that the Li abundances do not distingnish between various subgroups in I Per, in particular there is no distinction between the two age groups defined by Schild (1967). Other spectral features and their connection to subgroups in the association are discussed. In Section 7 the Ba n lines are discussed and a few remarks on the spectral properties of BC Cyg and RW Cep are given. Key words: late-type stars - NaD-Ha-Li abundance - I Per association