5. Results

5.1. Total magnitudes and surface brightness profiles

For estimation of total galaxy magnitudes in each band, integrated photometry was performed in increasing circular apertures from a prechosen center (see above) to faint outskirts of the galaxies. Aperture photometry of the observed galaxies is presented in Table 3, which is available only in electronic form in the CDS. The total magnitude was estimated as asymptotic value of the obtained radial growth curve. The asymptotic extrapolation was done by eye. The errors of the total magnitude determination are 0.06$^{\rm m}$ in B band, 0.08$^{\rm m}$ in V and 0.10$^{\rm m}$ in I. The results of our measurements are presented in Table 4, where the columns represent:

Column 1: galaxy name.

Columns 2, 3 and 4: total magnitudes in B, V and I band, respectively (not corrected for galactic absorption).

Columns 5 and 6: total colour B-V and V-I, respectively (not corrected for galactic absorption).

Column 7: radius (arcsec) at the surface brightness level of 25$^{\rm m}$/sq s in B band.

Column 8: total B-magnitude at this level (not corrected for galactic absorption).

Columns 9 and 10: same as 7 and 8, but for V band.

Columns 11 and 12: same as 7 and 8, but for I band.

Column 13: absolute B magnitude corrected for galactic absorption.

The blanks in Cols. 7-12 are due to the lack of surface brightness profiles for these galaxies (see below). The magnitude values for the galaxy UGC 5086 are uncertain because of extinction and marked with a colon.

Obtaining of the galaxy growth curves allows us also to trace the integrated colour changes with radius. B-V and V-I total colours versus galaxy radius from center are given in Fig. 2 for 33 galaxies of the sample.

Figure 2: The total B-V colour (solid line) and the total V-Icolour (dashed line) with respect to the radius from the galaxy center (arcsec)

Figure 2: continued

Figure 2: continued

The growth curves were not determined for the six dwarf galaxies (K 52, UGC 4483, F464-v3, UGC 5086, BK3N, K 73) because of significant measurement errors caused by the extremely low surface brightness of the object or by bright nearby background stars, which affects photometry results. For these six objects total magnitude and colour estimations were made only in one large circular aperture.

Note that most observed galaxies show a slow increase in the total B-Vcolour value from the center to the outer parts of the galaxy. Some spiral galaxies show the reverse colour gradient. For the most galaxies the V-I total colours follow B-V variations.

(V-I)₀ vs. (B-V)₀ (the total colours corrected for galactic absorption) are plotted in Fig. 3 for the measured galaxies (filled squares).

   

Table 4: Total magnitudes of the observed galaxies

Ident.	$B_{\rm T}$	$V_{\rm T}$	$I_{\rm T}$	$(B-V)_{\rm T}$	$(V-I)_{\rm T}$	R25(B)	B25	R25(V)	V25	R25(I)	I25	MB
UGC 3755	14.07	13.52	12.64	0.55	0.88	42.5	14.26	46.0	13.68	54.2	12.74	-14.39
NGC 2366	11.68	11.26	10.74	0.42	0.53	123.5	12.18	150.9	11.54	180.4	10.88	-16.17
UGC 3974	13.62	13.14	12.54	0.48	0.60	41.8	15.13	57.6	14.25	67.9	13.53	-14.69
K 52	16.35	16.11	15.55	0.24	0.56							-11.11
UGC 4459	14.55	14.14	13.49	0.45	0.65	33.6	15.35	41.8	14.66	52.1	13.87	-13.05
UGC 4483	14.95	14.51	14.02	0.44	0.49							-12.99
F464-v3	16.90	16.63	16.00	0.27	0.63							-11.81
UGC 5086	16.45:	15.89:	15.17:	0.56:	0.72:							-13.05:
Holmberg I	13.64	13.22	12.68	0.42	0.54	41.8	15.51	71.3	14.11	89.2	13.21	-15.66
UGC 5288	14.62	14.06	13.22	0.56	0.84	30.2	14.90	38.4	14.21	44.6	13.30	-14.71
BK3N	18.78	18.27	17.08	0.51	1.19							-8.83
Holmberg IX	14.53	14.31	13.49	0.22	0.82	29.5	15.95	32.2	15.61	56.9	14.30	-13.48
UGC 5423	14.42	13.90	13.48	0.52	0.42	33.6	14.68	38.4	14.08	53.5	13.53	-14.55
UGC 5692	13.57	12.66	11.36	0.90	1.30	53.5	14.10	80.3	12.95	122.1	11.46	-14.89
UGC 5918	15.00	14.58	13.78	0.42	0.80	21.3	16.62	30.9	15.65	56.9	14.16	-14.41
K 73	17.09	16.66	15.69	0.43	0.97							-11.03
UGC 6817	13.70	13.35	12.30	0.35	1.04	52.1	14.49	63.1	13.90	106.3	12.58	-14.38
NGC 4068	13.19	12.77	12.01	0.42	0.76	65.2	13.44	73.4	12.95	87.8	12.09	-15.49
NGC 4144	12.16	11.63	10.74	0.53	0.89	90.6	12.48	118.0	11.81	154.4	10.80	-17.86
NGC 4163	13.63	13.07	12.22	0.56	0.85	46.0	13.80	56.3	13.18	67.2	12.26	-14.21
PGC 38998	15.37	14.82	14.10	0.55	0.73	21.3	15.53	24.7	14.95	29.5	14.13	-15.73
UGC 7298	15.95	15.66	15.17	0.29	0.48	19.9	16.29	21.3	15.95	24.7	15.30	-13.83
UGC 7321	13.90	13.29	12.41	0.61	0.88	40.5	14.84	58.3	13.85	83.7	12.59	-14.65
IC 3308	15.41	14.96	13.94	0.45	1.02	20.6	15.80	22.6	15.33	36.4	14.31	-12.64
UGC 7577	12.95	12.36	11.36	0.59	1.00	76.1	13.41	94.7	12.69	142.7	11.51	-15.55
NGC 4449	10.06	9.65	8.85	0.42	0.79	164.6	10.10	187.3	9.66	222.0	8.80	-18.28
UGC 7698	13.53	13.18	12.49	0.35	0.69	55.6	14.71	65.9	14.02	91.9	12.98	-15.46
IC 3687	13.79	13.37	12.77	0.42	0.60	50.1	14.28	57.6	13.73	69.3	12.98	-13.68
IC 4182	12.02	11.60	10.72	0.42	0.88	123.5	12.31	140.6	11.78	173.6	10.73	-16.56
UGC 8201	13.31	12.97	12.27	0.34	0.70	66.5	13.69	77.5	13.24	101.5	12.39	-15.24
UGC 8308	15.45	15.10	14.34	0.39	0.70	26.8	15.85	28.1	15.39	36.4	14.46	-12.45
UGC 8320	12.97	12.53	11.99	0.44	0.54	72.0	13.40	85.8	12.88	100.2	12.18	-15.10
UGC 8331	14.46	14.17	13.62	0.29	0.55	35.7	15.03	41.8	14.49	46.6	13.79	-15.15
UGC 8508	14.12	13.67	12.88	0.45	0.79	41.8	14.42	52.1	13.83	61.7	12.99	-13.77
NGC 5229	14.33	13.85	13.05	0.48	0.80	39.1	14.68	43.9	14.02	43.9	13.15	-14.28
Holmberg IV	13.76	13.31	12.57	0.45	0.74	46.0	14.51	61.1	13.79	78.9	12.84	-15.90
NGC 5474	11.60	11.08	10.23	0.52	0.85	110.4	11.78	125.5	11.18	142.7	10.27	-17.73
NGC 6503	11.05	10.31	9.20	0.73	1.10	116.6	11.14	140.6	10.37	198.9	9.21	-17.68
NGC 6946	10.00	9.11	7.46	0.89	1.65	264.8	10.06	269.6	9.15	475.0	6.80	-20.38

For comparison, the integrated colours from the papers by Reshetnikov & Combes (1996) (circles) and Heraudeau & Simien (1996) (crosses) are also given in the figure. The galaxies from all the three works are well fitted by the following distribution: $(B-V)_0=0.85\times(V-I)_0-0.20$. This line is also plotted in Fig. 3.

Obtaining of azimuthally averaged surface brightness profiles was the next step of the reduction of the observed galaxies. These profiles have an advantage for dwarf galaxies of very low surface brightness and irregular structure (Karachentseva et al. 1996; Papaderos et al. 1996; Bremnes et al. 1998), because they allow the accuracy of the photometry in such galaxies to be improved.

Figure 3: (B-V)0 versus (V-I)0 for our sample galaxies (filled squares) and for the galaxies from the article of Heraudeau & Simien (1996) (crosses) and Reshetnikov & Combes (1996) (circles). The line of the regression for all galaxies is presented

Azimuthally averaged surface brightness profiles for our galaxies were obtained by differentiating the galaxy growth curves with respect to radius (Bremnes et al. 1998). The resulting profiles are shown in Fig. 4. Most of the galaxies are calculated till the level of 27- 28 mag/sq s in B band. Mean errors of the measurements were estimated by intercomparison of individual profiles for the same objects obtained from different frames in the same passband and they are of about 0.05$^{\rm m}$ at the 22 mag/sq s isophotal level and about 0.3-0.4 at the 27 mag/sq s isophotal level in each photometric band.

5.2. Photometric errors

Summing up all internal errors given above, we obtain the resulting errors of the total magnitude estimation to be about 0.18$^{\rm m}$ in B band, 0.18$^{\rm m}$ in V band and 0.19$^{\rm m}$ in I band and the resulting errors of surface brightness estimation to be about 0.17$^{\rm m}$ at the 22 mag/sq s isophotal level and about 0.35-0.45 at the 27 mag/sq s isophotal level in each photometric band.

External photometric errors can be estimated by a comparison of the total magnitudes of the observed galaxies with the published magnitudes of these galaxies. The comparison of the total B-magnitudes estimated in the present work with those given in the article of Bremnes et al. (1998) for seven galaxies in common, yields an agreement of 0.18 $\pm$ 0.04. A considerable systematic deviation may be caused by the uncertainty in the photometric calibration in the work of Bremnes et al., where they give information about the problems due to atmospheric extinction. A second similar work of the same authors has recently become available. A comparison of our data with those obtained by Bremnes et al. (1999), for seven common galaxies shows a good agreement of 0.07 $\pm$ 0.16.

Total magnitude estimates for some galaxies of our sample can be found in a number of papers. A comparison of these magnitudes with our data is given in Table 5, where the columns are:

   

Table 5: Comparison with magnitudes of other authors (see text)

Ident.	$\Delta B$	$\Delta V$	$\Delta I$	$\Delta (B-V)$	Reference
K 52	0.63		2.61		[5]
UGC 4459	-0.17				[6]
UGC 4483	-0.39				[6]
UGC 5086		0.66	1.08		[2]
Holmberg I	-0.13				[6]
BK3N	-0.18				[6]
UGC 5423	-1.00		-0.86		[5]
UGC 5692	-0.01				[6]
UGC 5918	-0.21				[6]
K 73	-0.17				[6]
NGC 4163	-0.30			0.11	[1]
UGC 7321	0.05	0.21			[4]
UGC 7577				0.14	[1]
UGC 7698	0.38			0.00	[3]
IC 3687	0.04			0.04	[3]
UGC 8308	-0.05				[7]
UGC 8320	-0.08				[7]
UGC 8331	0.19				[7]
UGC 8508	0.24				[7]
NGC 5229	0.23				[7]
Holmberg IV	0.11				[7]
NGC 5474	-0.17				[7]

Figure 4: The azimuthally averaged surface brightness profiles for the measured galaxies in B band (bottom lines), those in V band (middle lines) and those in I band (upper lines). The model profiles are shown by the dashed lines

Figure 4: continued

Figure 4: continued

Column 1: galaxy name.

Columns 2, 3 and 4: total magnitude difference in B, V and I band respectively.

Column 5: total B-V colour difference.

Column 6: reference to the work, where magnitudes for the comparison were taken. Here

1: work of Tikhonov & Karachentsev (1998), where galaxies were observed at the 6-m telescope of Special Astrophysical Observatory, Russia, and CCD field contained only $120'' \times 80''$.

2: article of Makarova & Karachentsev (1998).

3: article of Makarova et al. (1998) (in [2] and [3] the observations were carried out at the Nordic Optical Telescope with the CCD of $3' \times 3'$ field).

4: paper of Gavazzi, Boselli (1996).

5: article of Patterson & Thuan (1996) (note that, unlike for other works, there is no good agreement of our data with the magnitudes given in this paper).

6: work of Bremnes et al. (1998).

7: work of Bremnes et al. (1999).

The comparison of our blue total magnitudes and B-V colours with those given in the PGC yields a poor agreement: 0.63 $\pm$ 0.69 mag. The large scatter shows that the PGC magnitudes are considerably inhomogeneous. It is possible that the PGC total magnitudes used in photometric investigations may not provide good reliability.

The comparison directly of the aperture magnitudes in each photometric band, which are available for 26 of our galaxies in Prugniel & Heraudeau (1998), yields a good agreement: 0.00 $\pm$ 0.15 in B, 0.04 $\pm$ 0.14 in V, 0.09 $\pm$ 0.16 in I. Mean difference for each galaxy was found for the apertures (at least three) available. The results were then averaged for the all galaxies.