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We present the results of H I mapping with the NRAO2 VLA of one of the most metal-deÐcient blue compact dwarf (BCD) galaxies known, SBS 0335[052, with an oxygen abundance only 1/40 that of the Sun. We study the structure and dynamics of the neutral gas in this chemically young object with a spatial resolution of (D5.4 ] 3.9 kpc at an assumed distance of 54.3 Mpc), a sensitivity at the 20A .5 ] 15A 2 p detection level of D2.0 K or 7.5 ] 1019 cm~2 and a velocity resolution of 21.2 km s~1. We detected a large H I complex associated with this object having an overall size of about 66 by 22 kpc and elongated in the east-west direction. There are two prominent, slightly resolved peaks visible in the integrated H I map, separated in the east-west direction by 22 kpc (84A). The eastern peak is nearly coincident with the position of the optical galaxy SBS 0335[052. The western peak is about a factor of 1.3 brighter in the H I line and is identiÐed with a faint blue compact dwarf galaxy, SBS 0335[052W, with and a metallicity close to the lowest values known for BCDs, about 1/50 that of the Sun. m B \ 19.4, The radial velocities of both systems are similar, suggesting that the two BCDs, SBS 0335[052 and SBS 0335[052W, constitute a pair of dwarf galaxies embedded in a common H I envelope. Alternatively, the BCDs may be the nuclei of two distinct interacting primordial H I clouds. The estimated total dynamical mass, assuming the BCDs form a bound system, is larger than D6 ] 109 compared with a total M _ , gaseous mass and a total stellar mass Hence, the mass of the SBS M gas \ 2.1 ] 109 M _ M star ¹ 108 M _ . 0335È052 system is dominated by dark matter. Because of the disturbed H I velocity Ðeld and the presence of what might be tidal tails at either end of the system, we favor the hypothesis of tidal triggering of the star formation in this system. It can be due to either the nearby giant galaxy NGC 1376 or the mutual gravitational interaction of the two H I clouds.

We present the results of optical spectroscopy and imaging with the SAO 6 m telescope for the dwarf galaxy DDO 68 (UGC 5340 = VV 542), falling into the region of very low density of luminous (L > L * ) galaxies (Lynx-Cancer void). Its deep images in V, R bands and in the narrow Hα-filter show that this galaxy has the very irregular morphology, with a long curved tail on the South and a ring-like structure at the Northern edge. The latter consists of 5 separate regions, in three of which we could measure O/H by the classical T e method. Their weighted mean oxygen abundance corresponds to 12 + log (O/H) = 7.21 ± 0.03, coincident within uncertainties with those for I Zw 18. The (V − R) colour of DDO 68 is rather blue all over the galaxy, indicating the youth of its stellar populations. Comparing the (V − R) 0 colour of the underlying exponential disk of 0. m 12 ± 0.04 with the PEGASE.2 models for the evolving stellar clusters, we give the first estimate of the ages of the oldest stellar population, which needs confirmation by the other colours and the photometry of resolved stars. These ages are in the range of 200-900 Myr for continuous star formation law, and ∼100-115 Myr for the instantaneous starburst. We discuss the properties and the possible youth of this nearby object (∼2.3 times closer than the famous young galaxy I Zw 18) in the context of its atypical environment.

We present the results of high quality long-slit spectroscopy of planetary nebulae (PNe) and H ii regions in the two dwarf irregular galaxies Sextans A and B, which belong to a small group of galaxies just outside the Local Group. The observations were obtained with the ESO New Technology Telescope (NTT) multimode instrument (EMMI). In Sextans A we obtained the element abundances in its only known PN and in three H ii regions with the classical T e method. The oxygen abundances in these three H ii regions of Sextans A are all consistent within the individual rms uncertainties, with the average 12+log(O/H) = 7.54±0.06. The oxygen abundance of the PN in Sextans A is, however, significantly higher: 12+log(O/H) = 8.02±0.05. This PN is even more enriched in nitrogen and helium, suggesting a classification as a PN of Type I. The PN abundances of S and Ar, which are presumably unaffected by nucleosynthesis in the progenitor star, are well below those in the H ii regions, indicating lower metallicity at the epoch of the PN progenitor formation (∼1.5 Gyr ago, according to our estimates based on the PN parameters). In Sextans B we obtained spectra of one PN and six H ii regions. Element abundances with the T e method could be derived for the PN and three of the H ii regions. For two of these H ii 0 Based on observations obtained at the European Southern Observatory, La Silla, Chile (072.A-0087(B)).

Abstract. The work studies of the environment of low-mass galaxies with active star formation (SF) and a possible trigger of SF bursts due to gravitational interaction. Following the study by Taylor et al. (1995), we extend the search for possible disturbing galaxies of various masses to a much larger sample of 86 BCGs from the sky region of the Second Byurakan survey (SBS). The BCG magnitudes and radial velocities are revised and up-dated. The sample under study is separated by the criteria: EW ([Oiii] λ5007 ) > 45Å and V h < 6 000 km sand should be representative of all low-mass galaxies which experience SF bursts. We argue that the moderate tidal disturbers should be taken into account, and incorporate the respective range of distances in the search for disturbing neighbours. The majority of the neighbours in the vicinity of the studied BCGs are found through the study of their environment among UZC (Falco et al. 1999) galaxies, and the follow-up careful search of the fainter galaxies in the NED database. For the remaining BCGs, the neighbouring galaxies are found based on the results of the SAO 6 m telescope spectroscopy. By studing the data on the radial velocities of galaxies in the vicinity of BCGs we found: 1) 33 of the studied BCGs (∼38.5%) are associated with significantly brighter galaxies (∆B ≥ 1.5 m ); 2) 23 BCGs (∼26.5%) have neighbours either of comparable or significantly lower brightness; 3) 14 of the studied BCGs (16%) with no evident associated galaxy are either certain, or probable, mergers. Summarizing, we conclude that in ∼80% (or more) BCGs from the studied sample, the SF bursts are triggered either by tidal action of various strengths from other galaxies, or due to mergers of low-mass galaxies. We briefly discuss the implications of our main conclusion for evolutionary links of BCGs to other types of low-mass galaxies. Part of our sample falls into the volume belonging to the Local Supercluster. Therefore we formulate the results separately on the "Local Supercluster volume" and "general field region". The total fractions of BCGs likely triggered by interaction with other galaxy are respectively, ∼84.5% and 80% for the nearby volume and for the general field. The fractions of BCGs with significantly brighter disturbers in these two groups are seemingly different (∼54±14% vs. ∼31.5±7%, respectively). Among the so called "isolated" BCGs (that is, without a bright neighbouring galaxy) in both the Local Supercluster volume and in general field, ∼43± 10% are probably disturbed by dwarf galaxies and ∼26± 8% have a merger morphology. In the Appendix we present the results of the spectroscopy with the SAO 6 m telescope of 27 galaxies in an attempt to find possible disturbing galaxies in the vicinity of some of the sample BCGs.

In this paper we present results of a pilot study to use imaging data from the Sloan Digital Sky Survey (SDSS) to search for low-surface-brightness (LSB) galaxies. For our pilot study we use a test sample of 92 galaxies from the catalog of Impey et al. (1996) distributed over 93 SDSS fields of the Early Data Release (EDR). Many galaxies from the test sample are either LSB or dwarf galaxies. To deal with the SDSS data most effectively a new photometry software was created, which is described in this paper. We present the results of the selection algorithms applied to these 93 EDR fields. Two galaxies from the Impey et al. test sample are very likely artifacts, as confirmed by follow-up imaging. With our algorithms, we were able to recover 87 of the 90 remaining test sample galaxies, implying a detection rate of ∼96.5%. The three missed galaxies fall too close to very bright stars or galaxies. In addition, 42 new galaxies with parameters similar to the test sample objects were found in these EDR fields (i.e., ∼47% additional galaxies). We present the main photometric parameters of all identified galaxies and carry out first statistical comparisons. We tested the quality of our photometry by comparing the magnitudes for our test sample galaxies and other bright galaxies with values from the literature. All these tests yielded consistent results. We briefly discuss a few unusual galaxies found in our pilot study, including an LSB galaxy with a two-component disk and ten new giant LSB galaxies. 7 A "field" is SDSS terminology for an SDSS image covering ≈12 ′ ×10 ′ . 8 A "run" is one continuous scan obtained with the SDSS imaging camera. 9 The situation has improved with the latest version of the SDSS photometric pipeline, PHOTO version 5.4, which will be used for future data releases, but the shredding problems continue to persist.

Abstract. We present the results of high S/N long-slit spectroscopy with the Multiple Mirror and the SAO 6-m telescopes, optical imaging with the Wise 1-m telescope and H  observations with the Nançay Radio Telescope of the very metal-deficient (12 + log (O/H) = 7.64) luminous (M B = −18. m 1) blue compact galaxy (BCG) HS 0837+4717. The blue bump near λ4650, characteristic of WR stars is detected in the central supergiant H  region, as well as the barely seen red bump at λ5808. The derived number of WR stars in the region of the current starburst is ∼1000. Evidence for fast motions in this region is also seen as broad, low-contrast components in the Hα, Hβ and strong [O ] lines λλ4959,5007. While the extinction of the narrow emission lines from the supergiant H  region is low, the very large Balmer decrement of the broad components suggests that the part of current starburst is highly obscured by dust. Abundance ratios X/O for X = Ne, Ar, S, Fe and Cl in the supergiant H  region are in good agreement with the mean values of other very metal-deficient BCGs. Nitrogen, however, is overabundant by a factor of ∼6. This implies an unusually efficient N enrichment in HS 0837+4717, and probably, a non-typical evolution scenario. The Hα-line position-velocity (P−V) diagrams for directions approximately along the major and minor axes reveal disturbed motions of the ionized gas, mainly in peripheral regions. The SW part of the major axis P-V diagram looks like a rotation curve, with the velocity amplitude V rot ∼ 50−70 km s −1 at r = 4.3 kpc. Its NE part displays, however, strong deviations, indicating either counter-rotation, or a strong outflow/supershell. If it is considered as indicating a shell-like feature its velocity amplitude of ∼70 km s −1 (relative to the extrapolated rotation curve), and the apparent extent of ∼4 (3.3 kpc) imply a dynamical age of ∼14 Myr and the full energetic equivalent of ∼2.3 × 10 4 SNe. The latter indicates continuing starbursts during at least this time interval. The long-slit spectra reveal a complex morphology for this galaxy. It consists of two compact regions at a distance of ∼2 kpc. Their continuum flux differs by a factor of four. The brightest one is related to the current starburst with the age of ∼3.7 Myr. The slightly redder fainter component could be an older starburst (∼25 Myr). The Wise 1-m telescope UBVR integrated photometry reveals a high optical luminosity for this BCG, and the unusual (B − V) and (V − R) colours. The morphology of HS 0837+4717 is highly disturbed, with two small tails emerging to NNW and SSE. Such a disturbed overall morphology, a "double-nucleus" structure, significantly disturbed velocities of ionized gas, together with the very high power of the starburst suggests a possible explanation of the object as a recent merger. We compare the properties of this BCG and of similar objects known in the literature, and conclude that their high nitrogen excess is most probably related to the short phase of a powerful starburst when many WR stars contrib...

Abstract. We present the results of a neutral hydrogen survey of 79 galaxies from a statistical sample of 88 Blue Compact Galaxies (BCGs) selected from the First and Second Byurakan objective prism surveys to have a HII region-like spectrum, an equivalent width of the [O III] λ5007 line larger than ∼ 50Å, and a velocity ≤ 6000 km s −1 . The detection rate for the statistical sample is 74%. HI masses range between 4 10 7 M and 5 10 9 M with the HI mass distribution peaking at 3 10 8 M . The full width at half-maximum of the HI profile varies between ∼ 30 km s −1 and 160 km s −1 , with a mean of ∼ 92 km s −1 . These small widths are characteristic of dwarf galaxies. For comparison, we have also observed an additional 92 BCGs with weaker star formation and/or larger distances, and/or interesting astrophysical properties. These in general have larger widths and HI masses.