We investigate photometric properties of spiral arms and stellar complexes/associations inside these arms in the grand design NGC 628 (M 74) galaxy. We analyze GALEX ultraviolet, optical U BVRI, and Hα surface photometry data, including those obtained with 1.5 m telescope at the Maidanak Observatory. In the longer arm, the large and bright stellar complexes are located at regular intervals along the arm, but only farther from the galaxy center. They are joined with the narrow lane of dust, visible only in the infrared bands. The usual dust lane along the stellar arm inner side is seen there only at distances closer to the galaxy center. It is well expressed in CO (H 2 ) image. We have found, that the second, short arm hosts two dust lanes, the strong and wide at the inner side, and narrow and irregular along its outer edge. This outer dust lane is well seen in IR images only. The shorter arm contains no star complexes at all. Gradients of age and luminosity of stars across both arms are missing (again excepting the parts of arms located closer to the center), which is confirmed by our photometric cuts across both arms. The drastic difference in the morphology of the two symmetric arms (grand design type) of a galaxy has now been confirmed by objective measurements in the case of M 74. It is unclear why about two third of galaxies with beaded arms host these "beads" (star complexes) in one arm only.

Aims. We study brightness variations in the double lensed quasar UM673 (Q0142-100) with the aim of measuring the time delay between its two images. Methods. We combined our previously published observational data of UM673 obtained during the 2003-2005 seasons at the Maidanak Observatory with archival and recently observed Maidanak and CTIO UM673 data. We analyzed the V, R and I-band light curves of the A and B images of UM673, which cover ten observational seasons from August 2001 to November 2010. We also analyzed the time evolution of the difference in magnitudes (flux ratio) between images A and B of UM673 over more than ten years. Results. We find that the quasar exhibits both short-term (with an amplitude of ∼0.1 mag in the R band) and long-term (with an amplitude of ∼0.3 mag) variability on timescales of about several months and several years, respectively. These brightness variations are used to constrain the time delay between the images of UM673. From a cross-correlation analysis of the A and B quasar light curves and an error analysis we measure a mean time delay of 89 days with an rms error of 11 days. Given the input time delay of 88 days, the most probable value of the delay that can be recovered from light curves with the same statistical properties as the observed R-band light curves of UM673, is 95 +5 −16 +14−29 days (68% and 95% confidence intervals). Analysis of the V − I color variations and the V, R and I-band magnitude differences of the quasar images does not show clear evidence for microlensing variations between 1998 and 2010.

Spectroscopic observations of 63 H ii regions in six spiral galaxies (NGC 628, NGC 783, NGC 2336, NGC 6217, NGC 7331 and NGC 7678) were carried out with the 6‐m telescope (BTA) of Russian Special Astrophysical Observatory with the Spectral Camera attached to the focal reducer SCORPIO in multislit mode with a dispersion of 2.1 Å pixel−1 and a spectral resolution of 10 Å. These observations were used to estimate the oxygen and nitrogen abundances and the electron temperatures in H ii regions through the recent variant of the strong‐line method (NS calibration). The parameters of the radial distribution (the extrapolated central intercept value and the gradient) of the oxygen and nitrogen abundances in the discs of spiral galaxies NGC 628, NGC 783, NGC 2336, NGC 7331 and NGC 7678 have been determined. The abundances in NGC 783, NGC 2336, NGC 6217 and NGC 7678 are measured for the first time. Galaxies from our sample follow well the general trend in the luminosity–central metallicity diagram for spiral and irregular galaxies.

We study photometric properties, chemical abundances and sizes of star formation regions in the two principal arms of the galaxy NGC 628 (M74). The GALEX ultraviolet, optical U BVRI, and Hα surface photometry data are used, including those obtained with the 1.5-m telescope of the Maidanak Observatory. The thirty brightest star formation regions in ultraviolet light located in the spiral arms of NGC 628 are identified and studied. We find that the star formation regions in one (longer) arm are systematically brighter and larger than the regions in the other (shorter) arm. However, both luminosity and size distribution functions have approximately the same slopes for the samples of star formation regions in both arms. The star formation regions in the longer arm have a higher star formation rate density than the regions in the shorter arm. The regions in the shorter arm show higher N/O ratio at a higher oxygen abundance, but they have lower ultraviolet and Hα luminosities. These findings can be explained if we assume that star formation regions in the shorter arm had higher star formation rate in the past, but now it is lower than for those in the opposite arm. Results of stellar evolutionary synthesis show that the brightest regions in the longer arm are slightly younger than the ones in the shorter arm (3.5 ± 2.2 Myr versus 6.0 ± 1.1 Myr). Our results demonstrate that there is a difference in the inner structures and parameters of the interstellar medium between the spiral arms of NGC 628, one of which is long and hosts a regular chain of bright star formation complexes and the other, shorter one does not.

Hierarchical structures and size distribution of star formation regions in the nearby spiral galaxy NGC 628 are studied over a range of scale from 50 to 1000 pc using optical images obtained with 1.5 m telescope of the Maidanak Observatory. We found hierarchically structured concentrations of star formation regions in the galaxy, smaller regions with a higher surface brightness are located inside larger complexes having a lower surface brightness. We illustrate this hierarchy by dendrogram, or structure tree of the detected star formation regions, which demonstrates that most of these regions are combined into larger structures over several levels. We found three characteristic sizes of young star groups: ≈ 65 pc (OB associations), ≈ 240 pc (stellar aggregates) and ≈ 600 pc (star complexes). The cumulative size distribution function of star formation regions is found to be a power law with a slope of approximately −1.5 on scales appropriate to diameters of associations, aggregates and complexes. This slope is close to the slope which was found earlier by B. Elmegreen et al. for star formation regions in the galaxy on scales from 2 to 100 pc.