Neutral sodium D2 line in late-type stars

An atlas of high spectral resolution Na I D2 and HI alpha spectra is presented for 33 dwarfs giants, and supergiants covering a range of spectral types from F5 to M4.5. These spectra form the basis of a study in which the effects of a stellar chromosphere on the Na I D2 profile are investigated. The analysis of line profile parameters yields the following results: (i) a relationship between the line width and the luminosity for the giants and supergiants does not exist for Na I D2 as has been observed for Ca II K core emission (Wilson and Bappu, 1957) and H I alpha (Kraft et al., 1964). This reinforces the concept that the mechanism responsible for the Wilson-Bappu effect does not operate in the high photosphere of these stars. (ii) The correlation between Na I D2 line width and luminosity for the F through K dwarfs is explained in terms of differences in effective temperature and surface gravity along with the main sequences. The dMe stars exhibit central reversals in the Na I D lines. (iii) The method of Steinitz et al. (1975) has been used to measure Doppler widths for H I alpha and Na I D2 lines under the assumption of a constant properties atmosphere. The H I alpha measurements imply supersonic nonthermal velocities for the giants and supergiants