ALBERT

Description: We present observations of the H α, H β, [S ii] λλ6716, 6731 and [N ii] λ6583 emission lines in the galactic H ii region Sh2-235 with the Mapper of Narrow Galaxy Lines (MaNGaL), a tunable filter at the 1-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences. We show that the H ii region is obscured by neutral material with AV ≈ 2−4 mag. The area with the highest AV is situated to the south-west from the ionizing star and coincides with a maximum detected electron density of ≳300 cm−3. The combination of these results with archive AKARI far-infrared data allows us to estimate the contribution of the front and rear walls to the total column density of neutral material in S235 and explain the 3D structure of the region. The H ii region consist of a denser, more compact portion deeply embedded in the neutral medium and the less dense and obscured gas. The front and rear walls of the H ii region are inhomogeneous, with the material in the rear wall having a higher column density. We find a two-sided photodissociation region in the dense clump S235 East 1, illuminated by a UV field with G0 = 50−70 and 200 Habing units in the western and eastern parts, respectively.

Description: NGC 6946, known as the Fireworks galaxy because of its high supernova rate and high star formation, is embedded in a very extended H i halo. Its northern spiral arm is well detached from the galactic main body. We found that this arm contains a large (~300 pc in size) Red Ellipse, named according to a strong contamination of the Hα emission line on its optical images. The ellipse is accompanied by a short parallel arc and a few others still smaller and less regular; a bright star cluster is seen inside these features. The complicated combination of arcs seems to be unique; it is only a bit similar to some SNRs. However, the long-slit spectral data obtained with the Russian 6-m telescope did not confirm the origin of the nebula as a result of a single SN outburst. The emission-line spectrum corresponds to the photoionization by young hot stars with a small contribution of shock ionization. The most likely explanation of the Red Ellipse is a superbubble created by a collective feedback of massive stars in the star cluster located in the NE side of the Red Ellipse. However, the very regular elliptical shape of the nebulae seems strange.

Description: In this paper, we present results of a photometric and kinematic study for a sample of 13 edge-on spiral galaxies with pronounced integral shape warps of their stellar discs. The global structure of the galaxies is analysed on the basis of the Sloan Digital Sky Survey imaging, in the g , r and i passbands. Spectroscopic observations are obtained with the 6-m Special Astrophysical Observatory telescope. In general, galaxies of the sample are typical bright spiral galaxies satisfying the Tully–Fisher relation. Most of the galaxies reside in dense spatial environments and, therefore, tidal encounters are the most probable mechanism for generating their stellar warps. We carried out a detailed analysis of the galaxies and their warps and obtained the following main results: (i) maximum angles of stellar warps in our sample are about 20°; (ii) warps start, on average, between 2 and 3 exponential scalelengths of a disc; (iii) stronger warps start closer to the centre, weak warps start farther; (iv) warps are asymmetric, with the typical degree of asymmetry of about several degrees (warp angle); (v) massive dark halo is likely to preclude the formation of strong and asymmetric warps.

Description: We present the first results of our search for transiting exoplanet candidates as part of the Kourovka Planet Search (KPS) project. The primary objective of the project is to search for new hot Jupiters which transit their host stars, mainly in the Galactic plane, in the R c magnitude range of 11–14 mag. Our observations were performed with the telescope of the MASTER robotic network, installed at the Kourovka astronomical observatory of the Ural Federal University (Russia), and the Rowe-Ackermann Schmidt Astrograph, installed at the private Acton Sky Portal Observatory (USA). As test observations, we observed three celestial fields of size 2  x  2 deg 2 during the period from 2012 to 2015. As a result, we discovered four transiting exoplanet candidates among the 39 000 stars of the input catalogue. In this paper, we provide the description of the project and analyse additional photometric, spectral, and speckle interferometric observations of the discovered transiting exoplanet candidates. Three of the four transiting exoplanet candidates are most likely astrophysical false positives, while the nature of the fourth (most promising) candidate remains to be ascertained. Also, we propose an alternative observing strategy that could increase the project's exoplanet haul.

Description: Stellar population and the interstellar gas–dust medium in the vicinity of the open star cluster vdB 130 are analysed using optical observations taken with the 6 m telescope of the Special Astrophysical Observatory of Russian Academy of Sciences and the 125 cm telescope of the Sternberg Astronomical Institute, Lomonosov Moscow State University along with the data of Spitzer and Herschel . Based on proper motions and BV and JHK s Two Micron All Sky Survey photometric data, we select additional 36 stars as probable cluster members. Some stars in vdB 130 are classified as B stars. Our estimates of minimum colour excess, apparent distance modulus and the distance are consistent with young age (from 5 to 10 Myr) of the cluster vdB 130. We suppose the large deviations from the conventional extinction law in the cluster direction, with R V  ~ 4–5. The cluster vdB 130 appears to be physically related to the supershell around Cyg OB1, a cometary CO cloud, ionized gas and regions of infrared emission. There are a few regions of bright mid-infrared emission in the vicinity of vdB 130. The largest of them is also visible on Hα and [S ii ] emission maps. We suggest that the infrared blobs that coincide in projection with the head of the molecular cloud are H ii regions, excited by the cluster B stars. Some signatures of a shock front are identified between these IR-bright regions.

Description: Using three-dimensional (3D) spectroscopy with a scanning Fabry–Perot interferometer, we study the kinematics of ionized gas in 59 nearby dwarf galaxies. Combining our results with data from the literature, we provide a global relation between the gas velocity dispersion and the star formation rate (SFR) and Hα luminosity for galaxies with a very broad range of star formation rates: SFR = 0.001–300 M yr –1 . We find that the SFR– relation for the combined sample of dwarf galaxies, star-forming, local luminous and ultraluminous infrared galaxies can be fitted in the form SFR 5.3 ± 0.2 . This implies that the slope of the L – relation inferred from a sample of rotation-supported disc galaxies (including mergers) is similar to the L – relation of individual giant H ii regions. We present arguments that the velocity dispersion of the ionized gas does not reflect virial motions in the gravitational potential of dwarf galaxies and instead is determined mainly by the energy injected into the interstellar medium by ongoing star formation.

Description: We analyse the ionized gas kinematics in the star formation regions of the supergiant shell (SGS) of the IC 2574 galaxy using observations made with the Fabry–Perot interferometer at the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences; the data of the H i Nearby Galaxy Survey (THINGS) are used to analyse the neutral gas kinematics in the area. We perform the ‘derotation’ of the Hα and H i data cubes and show its efficiency in the kinematics analysis. We confirm the SGS expansion velocity of 25 km s –1 obtained previously and conclude that the SGS is located at the far side of the galactic disc plane. We determine the expansion velocities, kinematic ages and the required mechanical energy input rates for four star formation complexes in the walls of the SGS; for those remaining, we give the limiting values of the above parameters. A comparison with the age and energy input of the stellar population of the complexes shows that sufficient energy is fed to all H ii regions except one. We discuss in detail the possible nature of this region and that of another region, which was believed to be a supernova remnant, according to radio observations. We have measured the expansion velocity of the latter and we can confirm its identification as an old supernova remnant. Our observations have allowed us to identify a faint diffuse Hα emission inside the SGS, which was not been previously observed.

Description: Although thick stellar discs are detected in nearly all edge-on disc galaxies, their formation scenarios still remain a matter of debate. Due to observational difficulties, there is a lack of information about their stellar populations. Using the Russian 6-m telescope BTA we collected deep spectra of thick discs in three edge-on S0-a disc galaxies located in different environments: NGC 4111 in a dense group, NGC 4710 in the Virgo cluster, and NGC 5422 in a sparse group. We see intermediate age (4–5 Gyr) metal rich ([Fe/H] ~– 0.2...0.0 dex) stellar populations in NGC 4111 and NGC 4710. On the other hand, NGC 5422 does not harbour young stars, its disc is thick and old (10 Gyr), without evidence for a second component, and its α-element abundance suggests a 1.5–2 Gyr long formation epoch implying its formation at high redshift. Our results suggest the diversity of thick disc formation scenarios.

Description: This paper presents new results from the ongoing study of the unusual Lynx–Cancer void galaxy DDO 68, which has star-forming regions of record low metallicity [12+log (O/H) ~7.14]. The results include the following. (i) A new spectrum and photometry have been obtained with the 6-m SAO RAS telescope (BTA) for the luminous blue variable (LBV = DDO68-V1). Photometric data sets were complemented with others based on the Sloan Digital Sky Survey (SDSS) and the Hubble Space Telescope ( HST ) archive images. (ii) We performed an analysis of the DDO 68 supergiant shell (SGS) and the prominent smaller Hα arcs/shells visible in the HST image coupled with kinematic maps in Hα obtained with the Fabry–Perot interferometer (FPI) at the BTA. (iii) We compiled a list of about 50 of the most luminous stars (–9.1 mag 〈 M V 〈 –6.0 mag) identified from the HST images associated with the star-forming regions with known extremely low O/H. This is intended to pave the path for the current science to be investigated with the next generation of giant telescopes. We have confirmed earlier hints of significant variation of the LBV optical light, deriving its amplitude as V 3.7 mag for the first time. New data suggest that in 2008–2010 the LBV reached M V = –10.5 mag and probably underwent a giant eruption. We argue that the structure of star-forming complexes along the SGS (‘Northern Ring’) perimeter provides evidence for sequential induced star-formation episodes caused by the shell gas instabilities and gravitational collapse. The variability of some luminous extremely metal-poor stars in DDO 68 can currently be monitored with medium-size telescopes at sites with superb seeing.