Effective mean surface brightness (B-band): brief
The parameter brief (with its actual uncertainty sbrief) is the mean effective
surface brightness in B-band , i.e. the mean surface brightness inside the
effective aperture (the circular aperture enclosing one-half the total flux).
It is expressed in mag arcsec-2.
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-2 (
Dressler et al 1987),
brief = - 1.87 m'(Dn) + 60.13
where m'(Dn) = bt + 5 log(Dn) + 4.38
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
brief = 1.14 m'(LV) + 3.05 + 1.2 logr252
where m'(LV) is the average blue central surface brightness within
half total B-light (noted mu_e(LV) in
Launberts&Valentijn (1989))
The final value of brief is calculated as the weighted mean of
each determination.
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.