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We present the results of the first spectroscopic observations of two planetary nebula (PN) candidates in the Local Group dwarf irregular galaxy IC 10. Using several spectral classification diagrams, we show that the brightest PN candidate (PN 7) is not a PN, but rather a compact H ii region consisting of two components with low electron number densities. After the rejection of this PN candidate, the IC 10 PN luminosity function cut-off becomes very close to the standard value. With the compiled spectroscopic data for a large number of extragalactic PNe, we analyse a series of diagnostic diagrams to generate quantitative criteria for separating PNe from unresolved H ii regions. We show that, with the help of the diagnostic diagrams and the derived set of criteria, PNe can be distinguished from H ii regions with an efficiency of ∼99.6 per cent. With the obtained spectroscopic data, we confirm that another, 1.7 mag fainter PN candidate (PN 9) is a genuine PN. We argue that, based on all currently available PNe data, IC 10 is located at a distance of 725+63−33 kpc [distance modulus ]. [ABSTRACT FROM AUTHOR]

We present an X-ray study of our nearest starburst galaxy IC 10, based on XMM–Newton and Chandra observations. A list of 73 XMM–Newton and 28 Chandra detections of point-like X-ray sources in the field is provided; a substantial fraction of them are likely stellar objects in the Milky Way due to the low Galactic latitude location of IC 10. The brightest source in the IC 10 field, X-1, has a mean 0.3–8.0 keV luminosity of and shows a large variation by a factor of up to ∼6 on time-scales of ∼104 s during the XMM–Newton observation. The X-ray spectra of the source indicate the presence of a multicolour blackbody accretion disc with an inner disc temperature . These results are consistent with the interpretation of the source as a stellar mass black hole (BH), probably accreting from a Wolf–Rayet (W–R) star companion. We infer the mass of this BH to be if it is not spinning, or a factor of up to ∼6 higher if there is significant spinning. We also detect an apparent diffuse soft X-ray emission component of IC 10. An effective method is devised to remove the X-ray CCD-readout streaks of X-1 that strongly affect the study of the diffuse component in the XMM–Newton and Chandra observations. We find that the diffuse X-ray morphology is oriented along the optical body of the galaxy and is chiefly associated with starburst regions. The diffuse component can be characterized by an optically thin thermal plasma with a mean temperature of and a 0.5–2 keV luminosity of , representing only a small fraction of the expected mechanical energy inputs from massive stars in the galaxy. There is evidence that the hot gas is driving outflows from the starburst regions; therefore, the bulk of the energy inputs may be released in a galactic wind. [ABSTRACT FROM AUTHOR]

The nature of the synchrotron superbubble in the IC 10 galaxy is discussed using the results of our investigation of its ionized gas structure, kinematics and emission spectrum from observations made with the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences, and based on our analysis of the radio emission of the region. The hypernova explosion is shown to be a more plausible mechanism of formation of the synchrotron superbubble compared with the earlier proposed model of multiple supernova explosions. A compact remnant of this hypernova may be identified with the well-known X-ray binary X-1 – an accreting black hole. [ABSTRACT FROM AUTHOR]

We present the results of medium-resolution spectroscopy of 28 globular clusters (GCs) in six nearby galaxies of different luminosities and morphological types, situated in M33 (15 objects), M31 (three), IC10 (four), UGCA86 (four), Holmberg IX (one) and DDO71 (one) obtained at the Special Astrophysical Observatory 6-m telescope. Measurements of Lick absorption line indices and comparison with Simple Stellar Population models enabled us to obtain their spectroscopic ages, metallicities and -element to Fe abundance ratios. We found that all old- and intermediate-age GCs in our sample have low metallicities dex. Metal-rich clusters are young and are preferentially found in galaxies more massive than . The least massive dwarfs of our sample, DDO71 and Holmberg IX, host one massive intermediate-age and one massive young metal-poor GC, respectively. [ /Fe] abundance ratios tend to be enhanced but closer to solar values for dwarf galaxies compared to GCs in more massive galaxies. We analyse the age–metallicity relation for GCs in our sample and others from the literature, and find that (1) there is a general trend for GCs in low surface brightness dwarf galaxies to be more metal-poor at a given age than GCs in more massive galaxies; (2) the GC metallicity spread is wider for more massive galaxies and (3) intermediate-age GCs in early-type dwarf galaxies are more metal-rich at any given age than those in irregular galaxies of similar luminosity. [ABSTRACT FROM AUTHOR]