A volatility index for comets

Abstract

A volatility index, VI, as defined, measures the variations in total brightness of a comet when it is most active near perihelion. The highly consistent cometary magnitude measurements taken by Max Beyer determined the VI for 67 long-period (L-P) and 14 short-period (S-P) comets. The compilations performed by N.T. Bobrovnikoff provide additional values for 42 L-P and 3 S-P comets. Volatility does not correlate with period among the L-P comets and hence shows no “aging” effect. Similarly, the VI measurement averages are the same for S-P as for L-P comets and show no correlation with absolute magnitude near perihelion, with orbital inclination, nor with the activity index, which measures the intrinsic brightness change from great solar distances to the maximum near perihelion. The results suggest that active comets are basically alike regardless of their orbits or “ages”.