Abstract. We present optical spectroscopy of H ii regions in the Local Group galaxy IC 10 and UBV R photometry of foreground stars in three fields towards this galaxy. From these data, we find that the foreground reddening due to the Milky Way is E(B − V ) = 0.77 ± 0.07 mag. We find that IC 10 contains considerable internal dust, which qualitatively explains the variety of reddening values found by studies of its different stellar populations. Based upon our foreground reddening, IC 10 has intrinsic photometric properties like those of a blue compact dwarf galaxy, and not those of a dwarf irregular. This result is consistent with much evidence that IC 10 is in the throes of a starburst that began at least 10 Myr ago. We also report the discovery of a new WR star in the H ii region HL111c.Key words. galaxies: individual: IC 10 -galaxies: local group -galaxies: fundamental parameters -galaxies: starburst -galaxies: dwarf IntroductionIC 10 has long been recognized as a peculiar object (Hubble 1936), and is now considered the Local Group's representative of a starburst galaxy (van den Bergh 2000). As we will show, IC 10 may very well be the nearest example of a blue compact dwarf galaxy (BCD). Certainly, its surface brightness is similar to that seen in BCDs once we account for the foreground reddening. Among Local Group dwarf galaxies, IC 10 has the highest surface density of WR stars and the highest current rate of star formation (Mateo 1998). The presence of so many WR stars and the high Hα luminosity emphasize that IC 10 is undergoing a strong burst of star formation that began at Send offprint requests to: M. G. Richer, e-mail: richer@astrosen.unam.mx least 10 Myr ago. Observations of 21-cm emission from H i reveal that IC 10 consists of an inner disk embedded in an extended, complex, counter-rotating envelope (Shostak & Skillman 1989), and leads Wilcots & Miller (1998) to conclude that IC 10 is still in its formative stage. These H i observations emphasize the youth of the current star formation episode, for there is a notable lack of interstellar medium structures that are attributable to supernovae (Wilcots & Miller 1998). Several studies of the stellar populations in IC 10 have revealed the existence of young, intermediate-age, and old stellar populations (Massey & Armandroff 1995;Sakai et al. 1999;Borissova et al. 2000). However, with the exception of the very recent star formation, very little is known of the history of star formation in IC 10, and nothing is known of the star formation history outside of the star-forming region.Article published by EDP Sciences and available at http://www.aanda.org or http://dx

Abstract. We present Fabry-Perot and multi-object spectroscopy of the galaxies in Hickson compact group 31 (HCG 31). Based upon our Hα data cubes, galaxies A and C are a single entity, showing no discontinuity in their kinematics. Kinematically, galaxy E is probably a component of the A+C complex; otherwise it is a recently detached fragment. Galaxy F appears, both kinematically and chemically, to have formed from material tidally removed from the A+C complex. Galaxies B and G are kinematically distinct from this complex. Galaxy Q also has a radial velocity compatible with group membership. Galaxies A, B, C, and F have nearly identical oxygen abundances, despite spanning a luminosity range of 5 mag. Galaxy B's oxygen abundance is normal for its luminosity, while galaxy F's abundance is that expected given its origin as a tidal fragment of the A+C complex. The oxygen abundances in galaxies A and C are also understandable if the A+C complex is a late-type spiral suffering strong gas inflow and star formation as a result of a tidal interaction. Given the kinematics of both the galaxies and the H  gas, the oxygen abundances, and the position of galaxy G, we propose that an interaction of galaxy G with the A+C complex, rather than a merger of galaxies A and C, is a more complete explanation for the tidal features and other properties of HCG 31. In this case, the A+C complex need not be a merger in progress, though this is not ruled out.

We have searched for supernova remnants (SNRs) in the irregular galaxies IC 10 and NGC 4449 by means of Fabry-Perot interferometry in Hα and [SII] lines, complemented by radio continuum observations. We find several new SNR candidates in each galaxy in addition to the known ones. Although these galaxies have several common properties, the distributions of SNRs in each galaxy is different. This shows that the star formation mechanisms in these galaxies act in different ways, in favor of the formation of a large nebular HII complex in IC 10, similar to 30 Dor in the Large Magellanic Cloud. We are studying the conditions over which these different star formation histories take place.

In this work we report the search for nebulosities associated with the candidate Wolf-Rayet stars listed in Massey el al (1992) in the irregular galaxy IC 10, based upon Hα, [S II], and [O III] direct images and imaging Fabry-Pérot spectroscopy. Approximately 95% of the WR candidate stars we analyzed are found within nebulae. For most of these nebulae, we find broad wings on their Hα radial-velocity profiles. For some of the nebulae, the Hα velocity profiles are broadened with a typical velocity difference of 80–100 kms1.