This parameter is also derived indirectly from two other equivalent measurements ( Paturel et al 1997):

1) from the apparent diameter Dn enclosing a mean surface brightness of 23.75 B-mag arcsec

where

2) from the mean surface brightness "LV" inside the effective isophote (elliptical isophote enclosing one half the total flux) measured by Launberts&Valentijn (1989).

Similarly, we have

where

The final value of

**Effective radius**.
Using the definition of `brief` and `bt` one can derive the effective radius:
`5 log(re) = brief - bt - 1.995`, where `re` is the effective radius in arcsec (`1.995` stands for log(2pi)).
Note also that `re` measurements are also listed in the compilation of diameters, and
can be also derived from the catalogue of integrated photometry.

HyperLeda | Questions: prugniel@obs.univ-lyon1.fr |