Vol 45, No 3 (2019)

We have selected a sample of 326 young (log t < 8) open star clusters with the proper motions and distances calculated by various authors from Gaia DR2 data. The mean values of their line-of-sight velocities have also been taken from various publications. As a result of our kinematic analysis, we have found the following parameters of the angular velocity of Galactic rotation: Ω₀ = 29.34 ± 0.31 km s⁻¹ kpc⁻¹, Ω′₀ = −4.012 ± 0.074 kms⁻¹ kpc⁻², and Ω″₀ = 0.779 ± 0.062 kms⁻¹ kpc⁻³. The circular rotation velocity of the solar neighborhood around the Galactic center is V₀ = 235 ± 5 km s⁻¹ for the adopted Galactocentric distance of the Sun R₀ = 8.0 ± 0.15 kpc. The amplitudes of the tangential and radial velocity perturbations produced by the spiral density wave are f_θ = 3.8 ± 1.2 km s⁻¹ and f_R = 4.7 ± 1.0 km s⁻¹, respectively; the perturbation wavelengths are λ_θ = 2.3 ± 0.5 kpc and λ_r = 2.2 ± 0.5 kpc for the adopted four-armed spiral pattern. The Sun’s phase in the spiral density wave is close to χ_⊙ = −120° ± 10°.

We have performed a joint spectral and timing analysis of the outburst of GRS 1739-278 in 2014 based on Swift and INTEGRAL data. We show that during this outburst the system exhibited both intermediate states: hard and soft. Peaks of quasi-periodic oscillations (QPOs) in the frequency range 0.1–5 Hz classified as type-C QPOs have been detected from the system. Using Swift/BAT data we show that after the 2014 outburst the system passed to the regime of mini-outburst activity: apart from the three mini-outbursts mentioned in the literature, we have detected four more mini-outbursts with a comparable (∼20 mCrab) flux in the hard energy band (15–50 keV). We have investigated the influence of the accretion history on the outburst characteristics: the dependence of the peak flux in the hard energy band in the low/hard state on the time interval between the current and previous peaks has been found (for the outbursts during which the system passed to the high/soft state).

Based on the multicolor (BVRIJHKL) photometric observations of the active red giant PZ Mon performed for the first time in the winter season of 2017–2018, we have determined the main characteristics of the spotted stellar surface in a parametric three-spot model. The unspotted surface temperature is T_eff = 4730 K, the temperature of the cool spots is T_s = 3500 K, their relative area is about 41%, and the temperature of the warm spots is ∼4500 K with a maximum relative area up to 20%.The distribution of spots over the stellar surface has been modeled. The warm spots have been found to be distributed at various longitudes in the hemisphere on the side of the secondary component and are most likely a result of its influence.

An analysis of the SDO AIA observations of oscillations in a sunspot with a duration of 6 h has shown that powerful umbral flashes occur in local oscillation cells. The local oscillation spectrum has been found to be distorted by the short pulses produced by powerful flashes. For one of the single flashes we have managed to extract the undistorted local oscillation spectrum for this cell. The flash has turned out to occur against the background of local 3-min oscillations. A comparison of the observations in the 1600 and 1700 Å channels has shown that the most powerful flashes occur at the level of the upper photosphere below the temperature minimum. Powerful umbral flashes are observed in the form of single or recurrent short pulses with an interval of ∼20 min. This distinguishes them from the long-known less powerful flashes that are trains of pulses with intervals of ∼3 min. Both types of flashes find their explanation in terms of the hypothesis about the existence of a slow-wave subphotospheric resonator and various modes of its operation.