A method of spectral classification of F stars through photo-electric photometry with interference filters is described. Two classification indices are determined, one measuring the strength of the H? line, the other the Balmer discontinuity. Both indices are practically uninfluenced by interstellar reddening.Results of observations with the 82-inch reflector 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 error (one observation) of a (B-V) value predicted from the two classification indices is ± 0m.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 of the visual absolute magnitude M? is ± 0m.18. The comparison with the data mentioned above indicates that the influence of cosmical scatter on the predicted (B-V) and M? values is small, or negligible.Applications in the study of galactic structure are very briefly discussed.
- 1 - natural sciences ; 2 - physics & astronomy ; 3 - astronomy & astrophysics
- 1 - sciences appliquees, technologies et medecines ; 2 - sciences biologiques et medicales ; 3 - sciences biologiques fondamentales et appliquees. psychologie ; 4 - agronomie. sciences du sol et productions vegetales