Narrow-band photometry of Halpha for late-type stars.

Summary. Equivalent widths of Hoc are derived from photoelectric photometry with bandpasses of about 5 A and 50 A. The passbands are defined by a pressure- adjustable grating system; centering of the passbands is done for each star, on the basis of geocentric radial velocity. Results for thirty-two stars show a clear correlation with luminosity (as well as with temperature) and suggest that such observations may provide a practicable luminosity discriminant. Key words: late-type stars - narrow-band photometry - hydrogen line - luminosity effect