The photometric procedures are based on ESO's MIDAS package and follow the prescription of PaperIV, as detailed in the following. The images were bias-substracted and then flat-fielded by combining several dome flats. The background was determined by fitting a tilted plane to average intensities of frame areas unaffected by bright stars or the object itself. The fits were checked for correctness by applying the same procedure to the already background-substracted frame. The deviation from zero of the resulting plane was compared to the mean intensity of the substracted background. Remaining background gradients of up to 0.5% can be regarded as small enough for our purposes; we found values between 0.05 and 0.3%.

Table 2: Global photometric properties of the observed dwarf galaxies.
No. Galaxy $B_{\rm T}$ A_B $V_{\rm T}$ $R_{\rm T}$ $r^B_{\rm eff}$ $r^V_{\rm eff}$ $r^R_{\rm eff}$ $\langle\mu\rangle^B_{\rm eff}$ $\langle\mu\rangle^V_{\rm eff}$ $\langle\mu\rangle^R_{\rm eff}$ B-V B-R

1. UGC 288 15.31 0.33 14.68 14.28 6.12 4.13 4.31 21.24 19.76 19.45 0.63 1.03

2. UGC 685 13.97 0.25 13.79 13.25 21.44 23.25 24.88 22.63 22.62 22.23 0.18 0.72

3. UGC 1281 12.83: 0.20 11.73: 11.28: 26.99: 27.95: 28.30: 21.99: 20.96: 20.54: 1.10: 1.55:

4. NGC 1156 11.78 0.96 11.31 10.91 31.58 34.28 35.48 21.28 20.98 20.66 0.47 0.87

5. UGC 2684 15.93 0.61 15.31: 15.21 18.07 17.92: 19.19 24.21 23.58: 23.62 0.62 0.72

6. UGC 2689 14.75 0.64 13.73 13.12 8.26 8.03 7.64 21.33 20.25 19.53 1.02 1.63

7. UGC 2716 14.05 0.59 13.57 13.13 22.81 26.29 28.26 22.84 22.67 22.38 0.48 0.92

8. UGC 2905 14.41 1.35 14.29 13.97 12.13 13.21 13.04 21.83 21.89 21.55 0.12 0.44

9. UGC 3303 13.39 0.56 12.68 12.15 49.49 49.02 46.80 23.86 23.13 22.50 0.71 1.24

10. PGC 17716 12.24 3.17 12.17 11.86 51.08 43.94 42.66 22.78 22.38 22.01 0.07 0.38

11. A0554+07 16.45: 2.56 16.27: 15.90: 12.38: 13.61: 9.23: 23.91: 23.94: 22.73: 0.18: 0.55:

12. UGC 3476 14.96 1.02 14.45 14.02 11.48 12.58 13.86 22.26 21.95 21.73 0.51 0.94

13. UGC 3600 15.79 0.39 15.27 14.79 16.24 15.86 16.95 23.84 23.27 22.93 0.52 1.00

14. Kar 49 18.25: 0.35 17.50: 17.10: 13.46: 1309: 11.80: 25.89: 25.08: 24.46: 0.75: 1.15:

15. NGC 2337 13.10 0.38 12.52 12.12 19.27 21.57 21.68 21.52 21.19 20.80 0.58 0.98

16. Kar 50 17.88: 0.23 17.64: 17.54: 11.12: 11.94: 13.34: 25.11: 25.02: 25.16: 0.24: 0.34:

17. UGC 4115 15.11 0.12 23.29 23.94

18. NGC 2537 12.59 0.23 11.92 11.43 21.56 21.79 23.08 21.23 20.61 20.25 0.67 1.16

19. DDO 64 15.31 0.09 15.02 14.31 21.75 20.87 21.41 24.00 23.62 22.96 0.29 1.00

20. DDO 97 15.08 0.12 14.52 14.20 43.09 39.91 34.88 25.25 24.52 23.91 0.56 0.88

**Table 2:** Global photometric properties of the observed dwarf galaxies.
No.	Galaxy	$B_{\rm T}$	A_B	$V_{\rm T}$	$R_{\rm T}$	$r^B_{\rm eff}$	$r^V_{\rm eff}$	$r^R_{\rm eff}$	$\langle\mu\rangle^B_{\rm eff}$	$\langle\mu\rangle^V_{\rm eff}$	$\langle\mu\rangle^R_{\rm eff}$	B-V	B-R
1.	UGC 288	15.31	0.33	14.68	14.28	6.12	4.13	4.31	21.24	19.76	19.45	0.63	1.03
2.	UGC 685	13.97	0.25	13.79	13.25	21.44	23.25	24.88	22.63	22.62	22.23	0.18	0.72
3.	UGC 1281	12.83:	0.20	11.73:	11.28:	26.99:	27.95:	28.30:	21.99:	20.96:	20.54:	1.10:	1.55:
4.	NGC 1156	11.78	0.96	11.31	10.91	31.58	34.28	35.48	21.28	20.98	20.66	0.47	0.87
5.	UGC 2684	15.93	0.61	15.31:	15.21	18.07	17.92:	19.19	24.21	23.58:	23.62	0.62	0.72
6.	UGC 2689	14.75	0.64	13.73	13.12	8.26	8.03	7.64	21.33	20.25	19.53	1.02	1.63
7.	UGC 2716	14.05	0.59	13.57	13.13	22.81	26.29	28.26	22.84	22.67	22.38	0.48	0.92
8.	UGC 2905	14.41	1.35	14.29	13.97	12.13	13.21	13.04	21.83	21.89	21.55	0.12	0.44
9.	UGC 3303	13.39	0.56	12.68	12.15	49.49	49.02	46.80	23.86	23.13	22.50	0.71	1.24
10.	PGC 17716	12.24	3.17	12.17	11.86	51.08	43.94	42.66	22.78	22.38	22.01	0.07	0.38
11.	A0554+07	16.45:	2.56	16.27:	15.90:	12.38:	13.61:	9.23:	23.91:	23.94:	22.73:	0.18:	0.55:
12.	UGC 3476	14.96	1.02	14.45	14.02	11.48	12.58	13.86	22.26	21.95	21.73	0.51	0.94
13.	UGC 3600	15.79	0.39	15.27	14.79	16.24	15.86	16.95	23.84	23.27	22.93	0.52	1.00
14.	Kar 49	18.25:	0.35	17.50:	17.10:	13.46:	1309:	11.80:	25.89:	25.08:	24.46:	0.75:	1.15:
15.	NGC 2337	13.10	0.38	12.52	12.12	19.27	21.57	21.68	21.52	21.19	20.80	0.58	0.98
16.	Kar 50	17.88:	0.23	17.64:	17.54:	11.12:	11.94:	13.34:	25.11:	25.02:	25.16:	0.24:	0.34:
17.	UGC 4115	15.11	0.12			23.29			23.94
18.	NGC 2537	12.59	0.23	11.92	11.43	21.56	21.79	23.08	21.23	20.61	20.25	0.67	1.16
19.	DDO 64	15.31	0.09	15.02	14.31	21.75	20.87	21.41	24.00	23.62	22.96	0.29	1.00
20.	DDO 97	15.08	0.12	14.52	14.20	43.09	39.91	34.88	25.25	24.52	23.91	0.56	0.88

The calibration was done by imaging photometrically well known galaxies like M 81, NGC 1275 etc. Data from the literature (Hypercat) were used to fit the measured growth curve (cumulative intensity profile) of these galaxies to a set of integrated magnitudes at different apertures.

For each galaxy the center, as well as the ellipticity and position angle of the major axis, were determined at the isophotal level of $\sim$ $25~{\rm mag}/\ifmmode\hbox{\rlap{$\sqcap$ }$\sqcup$ }\else{\unskip\nobreak\hfil... ...$ } \parfillskip=0pt\finalhyphendemerits=0\endgraf}\fi\hbox{$^{\prime\prime}$ }$ by means of the ellipse fitting routine FIT/ELL3. These parameters were then used to obtain a growth curve (integrated light profile) by integrating the galaxy light in elliptical apertures of fixed center, ellipticity, and position angle of the major axis, but with increasing aperture. Keeping the center and shape parameters fixed along the integration is essential for the type of irregular galaxies we are dealing with here. If the center were left free by fitting ellipses to a series of isophotes, as is often done in the surface photometry of galaxies, the center would likely shift around by large amounts, and any mean radial surface brightness profile constructed from these ellipse fits would be physically meaningless. Fixing the center and shape of the ellipse for integration at a faint outer isophote ensures that these reference parameters are closely related to the underlying older, less "noisy'' stellar population and therefore also to the mass distribution of the galaxy.

The drawback of this procedure is that for most irregulars the approximate center of mass thus determined does not coincide with the center of light, i.e. with the brightest spot. One has only to look at an image of the Large Magellanic Cloud to see that the brightest HII region (30 Doradus in this case) in a dwarf irregular galaxy is typically lying off-center. In a mean profile which refers to the center of mass (as determined at a faint outer isophote) this would show up in a relatively flat central light profile, or even a light decrement in the central part (which is clearly the case in some of our profiles, see Fig. 2). But even so, we think this is the only way a mean profile is physically meaningful. In practise, e.g. when fitting an exponential, one would of course simply disregard the inner part of the profile.

Before doing the galaxy photometry, the frames were cleaned from disturbing foreground stars or background galaxies. This is of course also a basic problem of the photometry of irregulars. Depending on the resolution, a HII region might appear starlike and hence - erroneously - be erased. It is therefore mandatory that "disturbing'' discrete objects affecting the galaxy light are only removed when it is absolutely obvious that they do not belong to the galaxy. Differences in total magnitude, when comparing the results of different photometric studies, are sometimes due simply to a difference in the cleaning procedure (see Sect. 4.4).

Table 3: Model parameters of the observed dwarf galaxies.
No. Galaxy $(\mu^{\exp}_0)_B$ $(\mu^{\exp}_0)_V$ $(\mu^{\exp}_0)_R$ $1/\alpha_B$ $1/\alpha_V$ $1/\alpha_R$ $\Delta m_B$ $\Delta m_V$ $\Delta m_R$

1. UGC 288 22.98 22.27 21.80 9.11 9.07 8.96 0.87 0.80 0.76

2. UGC 685 21.96 21.64 21.13 13.90 13.91 14.29 0.27 0.13 0.10

3. UGC 1281 20.90 19.91 19.52 17.17 17.93 18.37 -0.10 -0.09 -0.08

4. NGC 1156 20.31 19.71 19.59 19.19 19.17 21.23 0.11 -0.01 0.04

5. UGC 2684 23.30 22.67 22.73 12.10 12.29 13.57 -0.04 -0.09 -0.14

6. UGC 2689 21.87 20.71 20.24 8.41 7.75 8.23 0.50 0.53 0.54

7. UGC 2716 23.24 22.84 22.41 22.10 24.37 24.77 0.47 0.33 0.31

8. UGC 2905 21.30 21.28 20.55 7.84 8.43 7.55 0.42 0.36 0.19

9. UGC 3303 23.07 22.17 21.66 38.45 33.45 33.64 -0.24 -0.13 -0.12

10. PGC 17716 21.90 21.43 21.05 36.82 29.69 29.18 -0.17 -0.10 -0.13

11. A0554+07 23.46 22.89 21.25 9.37 8.11 4.77 0.15 -0.92 -0.04

12. UGC 3476 21.54 21.34 21.16 7.29 8.42 9.56 0.27 0.26 0.24

13. UGC 3600 22.88 22.34 21.97 10.22 10.36 10.64 0.04 -0.01 0.04

14. Kar 49 25.10 24.51 23.75 10.39 13.91 9.50 -0.23 -0.71 -0.24

15. NGC 2337 21.59 20.78 20.64 16.47 15.52 17.40 0.39 0.30 0.32

16. Kar 50 23.20 23.09 23.36 5.17 5.30 6.04 -0.25 -0.17 -0.08

17. UGC 4115 22.66 12.71 0.03

18. NGC 2537 22.10 21.21 20.75 20.28 19.80 20.70 0.97 0.81 0.74

19. DDO 64 22.56 22.10 21.49 11.54 10.73 11.20 -0.06 -0.07 -0.07

20. DDO 97 24.33 23.82 23.29 26.03 26.80 24.52 0.17 0.16 0.14

No.	Galaxy	$(\mu^{\exp}_0)_B$	$(\mu^{\exp}_0)_V$	$(\mu^{\exp}_0)_R$	$1/\alpha_B$	$1/\alpha_V$	$1/\alpha_R$	$\Delta m_B$	$\Delta m_V$	$\Delta m_R$
1.	UGC 288	22.98	22.27	21.80	9.11	9.07	8.96	0.87	0.80	0.76
2.	UGC 685	21.96	21.64	21.13	13.90	13.91	14.29	0.27	0.13	0.10
3.	UGC 1281	20.90	19.91	19.52	17.17	17.93	18.37	-0.10	-0.09	-0.08
4.	NGC 1156	20.31	19.71	19.59	19.19	19.17	21.23	0.11	-0.01	0.04
5.	UGC 2684	23.30	22.67	22.73	12.10	12.29	13.57	-0.04	-0.09	-0.14
6.	UGC 2689	21.87	20.71	20.24	8.41	7.75	8.23	0.50	0.53	0.54
7.	UGC 2716	23.24	22.84	22.41	22.10	24.37	24.77	0.47	0.33	0.31
8.	UGC 2905	21.30	21.28	20.55	7.84	8.43	7.55	0.42	0.36	0.19
9.	UGC 3303	23.07	22.17	21.66	38.45	33.45	33.64	-0.24	-0.13	-0.12
10.	PGC 17716	21.90	21.43	21.05	36.82	29.69	29.18	-0.17	-0.10	-0.13
11.	A0554+07	23.46	22.89	21.25	9.37	8.11	4.77	0.15	-0.92	-0.04
12.	UGC 3476	21.54	21.34	21.16	7.29	8.42	9.56	0.27	0.26	0.24
13.	UGC 3600	22.88	22.34	21.97	10.22	10.36	10.64	0.04	-0.01	0.04
14.	Kar 49	25.10	24.51	23.75	10.39	13.91	9.50	-0.23	-0.71	-0.24
15.	NGC 2337	21.59	20.78	20.64	16.47	15.52	17.40	0.39	0.30	0.32
16.	Kar 50	23.20	23.09	23.36	5.17	5.30	6.04	-0.25	-0.17	-0.08
17.	UGC 4115	22.66			12.71			0.03
18.	NGC 2537	22.10	21.21	20.75	20.28	19.80	20.70	0.97	0.81	0.74
19.	DDO 64	22.56	22.10	21.49	11.54	10.73	11.20	-0.06	-0.07	-0.07
20.	DDO 97	24.33	23.82	23.29	26.03	26.80	24.52	0.17	0.16	0.14

3 Photometric procedures