BCD - Chalonge and Divan - 1952
Three quantities (D,
1
and
b) are defined over
the 3300-4600 Å portion of photographic prism spectra.
D measures the magintude of the Balmer discontinuity,
1 indicates the effective
location of the Balmer discontinuity in the spectrum
and
b is related to the slope
of the continuum in the blue region of the spectrum longward of the Balmer discontinuity
( 3800 - 4800 Å ) [65] .