The uvby photometric system


A method for spectral classification of F stars through photo-electric photometry with interference filters is described. Two classification indices are determined, one measureing the strength of the Hbeta line, the other the Balmer discontinuity. Both indices are practically uninfluenced by interstellar reddening.

Results of observations with the 82-inch telescope of the McDonald Observatory in February and March, 1953, are compared with spectral classification by W.W. Morgan, with colour indices (B-V) on Harold Johnson's system, and with absolute magnitudes from trigonometric parallaxes and spectroscopic determinations.

The photometric probable errors (one observation) of a (B-V) value predicted from the two classification indices is +-0.006, corresponding to a probable error +-0.02 of a spectral class. The photometric probable error (one observation) of a predicted value of the visual absolute magnitude Mv is +-0.18. The comparison with the data mentioned above indicates that the influence of cosmical scatter on the predicted (B-V) and Mv values is small, or negligible.

Applications in the study of galactic structure is briefly discussed.
Last update: 3 December 1996