The reduction of apparent B-magnitude to the RC3-system of magnitudes
with photoelectric zero-point has been studied recently
(Paturel et al. 1994). Apparent B-magnitudes reduced to the RC3-system
will be designated as bt.
Several effects were taken into account. The reduction of a given
magnitude m to bt is given by:
where a, b, c, d, e, f, 
, <t>,
, <de1950>
are constant values given in Paturel et al. (1994, Table 6).
The mean bt magnitude is calculated as a weighted mean
where the weight is derived for each source of magnitude
as the inverse square of the mean standard deviation. The final
actual uncertainty sbt is derived from the total weight.
The cumulative completeness curve logN vs. bt is shown in Fig. 7 (click here). The completeness in apparent magnitude is satisfied up to bt=15.5. Apparent total magnitude bt is available for 76760 galaxies. The histogram of actual uncertainties sbt on bt is given in Fig. 8 (click here). More than 7 000 galaxies have an actual uncertainty on bt smaller than 0.02 mag.
Note that apparent diameter can be roughly converted into a magnitude m assuming that the mean surface brightness is constant for all galaxies. The conversion can be made using the relationship (Di Nella & Paturel 1994):
The standard deviation on m is about 0.5 mag. Using this relation, it is possible to obtain an estimate of the apparent magnitude for 93062 galaxies, 76760 magnitudes of which come from bt and 16302 from logd25. This magnitude m will be used for drawing a more general completeness curve (Fig. 11 (click here)).
Figure 7: Completeness curve for apparent magnitude bt.
The completeness is satisfied up
to the limit bt=15.5
Figure 8: Histogram of actual uncertainty on apparent magnitudes bt
Apparent bt magnitudes are corrected for galactic extinction, inclination and redshift effects according to the relation:
where ag is the galactic extinction in B (see Sect. 4), expressed in
magnitude, ak is taken from de Vaucouleurs et al. (1976, RC2 p33, rel.25),
v is the heliocentric velocity in 
(Sect. 9)
and ai is given by Bottinelli et al. (1995) as:
where, 
is taken from Simien & de Vaucouleurs (1986),
as a function of the morphological type code.
is taken from Fouqué & Paturel (1985) as seen
before (Sect. 6),
C=0.04 (Bottinelli et al. 1995) and 
.
Note that this relation has been demonstrated for spiral galaxies only.
For early type galaxies (t<0) we assume ai=0, in agreement with
de Vaucouleurs et al. (1991).
Colors are given in the UBV system
.
They are:
total asymptotic colors ubt for 
; bvt for 
and effective colors (i.e. colors within the effective aperture in which
half the total B-flux is emitted) ube for 
; bve for
.
Total asymptotic colors are corrected for galactic extinction,
inclination and redshift effects according to RC3. The corrected
colors are bvtc and ubtc for 
and 
respectively.