Multifrequency Method for Mapping Active Galactic Nuclei with Allowance for the Frequency-Dependent Image Shift

We consider the problem of multifrequency VLBA image synthesis and spectral-index mapping for active galactic nuclei related to the necessity of taking into account the frequency-dependent image shift. We describe our generalized multifrequency synthesis algorithm with a spectral correction based on the maximum entropy method. The results of our processing of multifrequency VLBI data for the radio sources J2202+4216, J0336+3218, and J1419+5423 are presented.Comment: 12 pages, 2 tables, 6 figure

Peculiarities of Open Star Clusters with High Vertical Velocities from the Region of the Sco-Cen OB Association

We have studied the kinematics of a unique sample of young open star clusters (OSCs) with high vertical velocities, $15<W<40$ km s$^{-1}$. The characteristics of these clusters were taken from the catalogue by Hunt and Reffert (2023), where their mean proper motions, line-of-sight velocities, and distances were calculated using Gaia DR3 data. These OSCs are located within 0.6 kpc of the Sun and form two clumps: one in the region of the Sco-Cen OB association and the other one in the region of the Per OB3-Per OB2 associations. The OSC group of 47 members in the region of the Sco-Cen association is shown to expand along the $y$ axis, $\partial V/\partial y=51\pm12$ km s$^{-1}$ kpc$^{-1}$. This group also has a positive rotation around the $z$ axis with an angular velocity of $71\pm11$ km s$^{-1}$ kpc$^{-1}$ and a negative rotation around the $x$ axis with an angular velocity of $-35\pm5$ km s$^{-1}$ kpc$^{-1}$. Based on the velocities of 27 OSCs from the region of the Per OB3-Per OB2 associations, we have found no gradients differing significantly from zero. We have studied the kinematics of more than 1700 stars selected by Luhman (2022) as probable members of the Sco-Cen OB association. These stars are shown to have no high vertical velocities. The expansion coefficient of the stellar system in the $xy$ plane has been found from all stars to be $K_{xy}=43.2\pm2.2$ km s$^{-1}$ kpc$^{-1}$. Based on stars from the three UCL, LCC, and V1062 Sco groups with a mean age $\sim$20 Myr, for the first time we have found a volume expansion coefficient of the stellar system differing significantly from zero, $K_{xyz}=43.2\pm3.4$ km s$^{-1}$ kpc$^{-1}$.Comment: 13 pages, 7 figures, 0 table

Determination of the Spiral Pattern Speed in the Milky Way from Young Open Star Clusters

We have estimated the spiral pattern speed in the Galaxy $\Omega_p$ from a large sample of young open star clusters (OSCs). For this purpose, we have used 2494 OSCs younger than 50 Myr. Their mean proper motions, line-of-sight velocities, and distances were calculated by Hunt and Reffert (2023) based on data from the Gaia~DR3 catalogue. Three methods have been applied to estimate $\Omega_p$. They all are based on the linear Lin-Shu spiral density wave theory. We have obtained an estimate of $\Omega_p=24.26\pm0.52$~km s$^{-1}$ kpc$^{-1}$ by the first method, which is most reliable in our view, using the velocity perturbations $f_R$ and $f_\theta$ found through a spectral analysis of the radial, $V_R$, and residual rotation, $\Delta V_{\rm circ},$ velocities. Using the second method, we have found the velocity perturbations $f_R$ and $f_\theta$ by solving the basic kinematic equations together with the Galactic rotation parameters and obtained an estimate of $\Omega_p= 23.45\pm0.53$~km s$^{-1}$ kpc$^{-1}$. We have found $\Omega_p= 28.9\pm2.8$~km s$^{-1}$ kpc$^{-1}$ by the third method based on an analysis of the position angles of OSCs at their birth time $\theta_{\rm birth}$.Comment: 15 pages, 5 figures, 1 table. arXiv admin note: text overlap with arXiv:2203.12902, arXiv:1903.09313, arXiv:2207.0341