Two luminosity effects in the spectra of late-type supergiants.

Two luminosity effects in GO to M2 supergiants have been examined, using 13 A mm -1 coude' spectrograms in the red. First, the width of the photospheric lines increases dramatically with luminosity. The rate of increase is about 6 km 1 per luminosity class, independent of temperature. Second, the appearance of Ha changes systematically with luminosity. The absorption component becomes broader and blueshifted from the rest velocity to a maximum of 80 km 1, while the emission component increases in strength on the shortward wing of the Ha absorption. Both effects may be used to assign luminosity classes by visual inspection of moderately high dispersion spectrograms. The extremely luminous G supergiant BS 8752 has a second Ha emission component, due to the same gas shell that gives rise to [N ii] AA6548, 6584 emission lines. The photospheric and Ha line widths are well correlated, indicating that the increase of macroturbulence with atmospheric height seen in the Sun appears to hold for supergiants as well. Subject headings: stars: late-type - stars: luminosities - stars: supergiants