Vol 42, No 11 (2016)

Open star clusters from the MWSC (Milky Way Star Clusters) catalogue have been used to determine the Galactic rotation parameters. The circular rotation velocity of the solar neighborhood around the Galactic center has been found from data on more than 2000 clusters of various ages to be V₀ = 236 ± 6 km s⁻¹ for the adopted Galactocentric distance of the Sun R₀ = 8.3 ± 0.2 kpc. The derived angular velocity parameters are Ω₀ = 28.48 ± 0.36 km s⁻¹ kpc⁻¹, Ω’₀ = −3.50 ± 0.08 km s⁻¹ kpc₋₂, and Ω″₀ = 0.331 ± 0.037 km s⁻¹ kpc⁻³. The influence of the spiral density wave has been detected only in the sample of clusters younger than 50 Myr. For these clusters the amplitudes of the tangential and radial velocity perturbations are f^θ = 5.6 ± 1.6 km s⁻¹ and f_R = 7.7 ± 1.4 km s⁻¹, respectively; the perturbation wavelengths are λ_θ = 2.6 ± 0.5 kpc (i_θ = ⁻¹1◦ ± 2◦) and λ_R = 2.1 ± 0.5 kpc (i_R = −9◦ ± 2◦) for the adopted four-armed model (m = 4). The Sun’s phase in the spiral density wave is (χ_⊙)_θ = −62◦ ± 9◦ and (χ_⊙)_R = −85◦ ± 10◦ from the residual tangential and radial velocities, respectively.

The electromagnetic field in a magnetized neutron star and the underlying volume charges and currents are found. A general case of a rigidly rotating neutron star with infinite conductivity, arbitrary distribution of the internal magnetic field, arbitrarily changing angular velocity, and arbitrary surface velocity less than the velocity of light is considered. Quaternions are used to describe rotation and determine the magnetic field. It is shown that the charge density is not equal to and can exceed significantly the common Goldreich–Julian density. Moreover, corrections to the magnetic field due to stellar rotation are zero. For a rotating neutron star, twisting magnetic field lines causes charge accumulation and current flows. This fact shows a possible link between changing internal magnetic field topology and observed activity of neutron stars.

We present the results of our UBV and JHKLM photometry for the semiregular pulsating variable V1027 Cyg, a supergiant with an infrared excess, over the period from 1997 to 2015 (UBV) and in 2009–2015 (JHKLM). Together with the new data, we analyze the photometric observations of V1027 Cyg that we have obtained and published previously. Our search for a periodicity in the UBV brightness variations has led to several periods from P = 212^d to 320^d in different time intervals. We have found the period P = 237^d based on our infrared photometry. The variability amplitude, the lightcurve shape, and themagnitude of V1027 Cyg atmaximum light change noticeably from cycle to cycle. The deepest minimum was observed in 2011, when the amplitudes of brightness variations in the star reached the following values: ΔU = 1_.^m28, ΔB = 1_.^m10, ΔV = 1_.^m05, ΔJ = 0_.^m30, ΔH = 0_.^m35, ΔK = 0_.^m32, ΔL = 0_.^m26, and ΔM = 0_.^m10. An ambiguous correlation of the B − V and U − B colors with the brightness has been revealed. For example, a noticeable bluing of the star was observed during the deep 1992, 2008, and 2011 minima, while the variations with smaller amplitudes show an increase in B − V at the photometric minima. The spectral energy distribution for V1027 Cyg from our photometry in the range 0.36 (U)–5.0 (M) μm corresponds to spectral types from G8I to K3I at different phases of the pulsation cycle. Low-resolution spectra of V1027 Cyg in the range λ4400–9200 ˚A were taken during 16 nights over the period 1995–2015. At the 1995 and 2011 photometric minima the star’s spectrum exhibited molecular TiO bands whose intensity corresponded to spectral types M0–M1, while the photometric data point to a considerably earlier spectral type. We hypothesize that the TiO bands are formed in the upper layers of the extended stellar atmosphere. We have measured the equivalent widths of the strongest absorption lines, in particular, the infrared Ca II triplet in the spectrum of V1027 Cyg. The calcium triplet (Ca T) with W_λ(Ca T) = 20.3 ± 1.8 ˚A as a luminosity indicator for supergiants places V1027 Cyg in the region of the brightest G–K supergiants. V1027 Cyg has been identified with the infrared source IRAS 20004+2955 and is currently believed to be a candidate for post-AGB stars. The evolutionary status of the star and its difference from other post-AGB objects are discussed.