Dwarf galaxies are believed to hold a key to the understanding of the structure and evolution of galaxies in general. A prerequisite for useful knowledge of dwarf galaxies is a thorough study of their systematic properties. Owing to the general low surface brightness of dwarf galaxies, it is most natural to pursue such a study in the "local'' volume, out to a distance of ca. 10 Mpc. Approximately 300 galaxies are presently known to lie in this volume (Schmidt & Boller 1992; Karachentsev et al. 1999); most of these are clustered in a number of well-known groups of galaxies, including the Local Group (LG).
In a series of papers (Bremnes et al. 1998; Bremnes et al. 1999; Bremnes et al. 2000), hereafter Papers I, III, and IV, B and R photometry of 61 dwarf galaxies in the northern M81 and M101 groups, and the CVnI cloud was presented. These data were used, together with data for another ca. 60 local dwarfs taken from the literature, to carry out a preliminary analysis of the photometric differences among dwarf galaxies in different environments, in particular by comparing these local, low-density environment dwarfs (lying in groups and clouds) with a sample of high-density environment dwarfs (lying in the nearby Virgo and Fornax clusters of galaxies). At a given total magnitude, dwarf galaxies of any given type (elliptical or irregular) appear to have significantly higher surface brightness in the local volume than in clusters, clearly indicating a difference in the evolutionary history between non-cluster and cluster dwarfs (Bremnes 2001, Paper V). This is probably the first statistical evidence for an environmental difference in the photometric structure among dwarfs of a given type. Note that this is more than just a dependence of the mixture (relative abundance) of the dwarf types with the environment (local galaxy density), which was known before (Binggeli et al. 1987, 1990).
Continuing this series of papers, we here present photometric data for 19 field (non-group) dwarf galaxies in the northern sky in the Cousins B, V and R bands. The basic motivation is simply to enlarge the sample of nearby dwarfs with known photometry in order to provide a more complete data set for comparative dwarf studies in the future. A particular goal is to confirm and refine the interesting trends found by Bremnes (2001) with more and better data. The present paper is a modest contribution to this goal; there are still up to 100 nearby dwarf candidates left to image. On the other hand, most dwarfs in the local volume presently available, as in Bremnes (2001), are group members. With the present imaging of 19 field dwarfs (or, rather, 18, as one turned out to be a likely background galaxy) we essentially double the number of field (non-group) dwarfs. This will therefore allow us to do a first, crude comparison between group and field dwarfs. A more detailed statistical analysis of the present data, together with those from our previous and future photometry of nearby dwarf galaxies, is left to a future paper of this series.
One of the difficulties when working with field galaxies is that individual distances are required for any meaningful photometry. Thanks to the enormous efforts of Karachentsev and colleagues, rough individual distances, mostly based on the magnitudes of the brightest resolved blue stars in a star forming galaxy, are known for most field dwarf galaxies (e.g., Karachentsev et al. 1999, and references therein).
In the following section we describe the sample and the imaging of the selected dwarf objects. The description of the reduction procedure follows in Sect. 3. In Sect. 4 we present the surface brightness profiles and the derived model-free parameters (total magnitude, effective radius and effective surface brightness); the best-fitting exponential model parameters (extrapolated central surface brightness and exponential scale length); the B-V colour profiles and gradients; and finally an assessment of the photometric accuracy. Notes on the individual galaxies observed are given in Sect. 5. In Sect. 6 we compare our present field dwarf data with that from previous work. Finally, our conclusions are given in Sect. 7.
| No. | Ident. 1 | Ident. 2 | RA | Dec | Type |  |
 |
Dist. | MB |
| 1. | UGC 288 | PGC 1777 | 00 29 03.60 | +43 25 54.0 | Im | 15.31 | 188 | 6.7 | -13.82 |
| 2. | UGC 685 | PGC 3974 | 01 07 22.40 | +16 41 02.0 | Im/BCD | 13.97 | 157 | 6.0 | -14.92 |
| 3. | UGC 1281 | PGC 6699 | 01 49 31.39 | +32 35 19.5 | Sd | 12.83: | 156 | 5.4 | -15.83: |
| 4. | NGC 1156 | UGC 2455 | 02 59 42.61 | +25 14 17.1 | IBm | 11.78 | 375 | 7.8 | -17.68 |
| 5. | UGC 2684 | PGC 12514 | 03 20 23.71 | +17 17 45.1 | Im | 15.93 | 350 | 6.5 | -13.13 |
| 6. | UGC 2689 | PGC 12585 | 03 21 27.67 | +40 48 06.1 | S0 | 14.75 | |||
| 7. | UGC 2716 | PGC 12719 | 03 24 07.60 | +17 45 10.0 | Sm | 14.05 | 379 | 6.7 | -15.08 |
| 8. | UGC 2905 | PGC 14149 | 03 57 00.14 | +16 31 20.8 | Im | 14.41 | 292 | 5.8 | -14.41 |
| 9. | UGC 3303 | PGC 17250 | 05 24 59.50 | +04 30 18.0 | Sd: | 13.39 | 522 | 7.2 | -15.90 |
| 10. | PGC 17716 | Orion Dw. | 05 45 01.63 | +05 03 41.2 | SBd: | 12.24 | 366 | 6.4 | -16.79 |
| 11. | A0554+07 | 05 57 33.5 | +07 28 57 | Im | 16.45: | 411 | 5.5 | -12.25: | |
| 12. | UGC 3476 | PGC 19162 | 06 30 29.22 | +33 18 07.2 | Im (pec) | 14.96 | 469 | 7.0 | -14.26 |
| 13. | UGC 3600 | PGC 19871 | 06 55 40.00 | +39 05 42.8 | Im | 15.79 | 412 | 7.3 | -13.53 |
| 14. | Kar 49 | 07 07 30.00 | +71 52 47 | dE: | 18.25: | ||||
| 15. | NGC 2337 | UGC 3711 | 07 10 13.49 | +44 27 24.2 | IBm/BCD | 13.10 | 436 | 7.9 | -16.39 |
| 16. | Kar 50 | PGC 22060 | 07 52 47.40 | +61 23 23.0 | Im | 17.88: | |||
| 17. | UGC 4115 | PGC 22277 | 07 57 01.80 | +14 23 27.0 | Im | 15.11 | 338 | 5.3 | -13.51 |
| 18. | NGC 2537 | UGC 4274 | 08 13 14.57 | +45 59 28.2 | Sm/BCD | 12.59 | 447 | 6.9 | -16.60 |
| 19. | DDO 64 | UGC 5272 | 09 50 22.40 | +31 29 16.0 | Im | 15.31 | 520 | 7.1 | -13.95 |
| 20. | DDO 97 | UGC 6782 | 11 48 57.24 | +23 50 16.4 | Im | 15.08 | 525 | 14.0 | -15.65 |
Copyright ESO 2001