Galactic Parameters from Masers with Trigonometric Parallaxes

Spatial velocities of all currently known 28 masers having trigonometric parallaxes, proper motion and line-of-site velocities are reanalyzed using Bottlinger's equations. These masers are associated with 25 active star-forming regions and are located in the range of galactocentric distances 3<R<14 kpc. To determine the Galactic rotation parameters, we used the first three Taylor expansion terms of angular rotation velocity {\Omega} at the galactocentric distance of the Sun R0=8 kpc. We obtained the following solutions: {\Omega}o=-31.0 +/- 1.2 km/s/kpc, {\Omega}o'=4.46 +/- 0.21 km/s/kpc^2, {\Omega}o"=-0.876 +/- 0.067 km/s/kpc^3, Oort constants: A=17.8 +/- 0.8 km/s/kpc, B=-13.2 +/- 1.5 km/s/kpc and circular velocity of the Solar neighborhood rotation Vo=248 +/- 14 km/s. Fourier analysis of galactocentric radial velocities of masers VR allowed us to estimate the wavelength {\lambda}=2.0 +/- 0.2 kpc and peak velocity f_R=6.5 +/- 2 km/s of periodic perturbations from the density wave and velocity of the perturbations 4 +/- 1 km/s near the location of the Sun. Phase of the Sun in the density wave is estimated as {\chi}o ~ -130^o +/- 10^o. Taking into account perturbations evoked by spiral density wave we obtained the following non-perturbed components of the peculiar Solar velocity with respect to the local standard of rest (LSR) (Uo,Vo,Wo)LSR=(5.5,11,8.5) +/- (2.2,1.7,1.2) km/s.Comment: 8 pages, 1table, 9 figures, accepte

Experience of high resolution VLBI imaging using generalized maximum entropy method

The generalized maximum entropy method (GMEM) is a special modification of the standard maximum entropy method (MEM) which seeks solutions in the space of complex functions. In this work a reduced version of the GMEM intended for reconstructing real images with positive and negative values is used. As compared with the standard MEM, intended for the reconstruction of only non-negative images, the GMEM allows us to obtain higher-quality images with a much lower level of nonlinear distortions caused by errors in the data. Here, we present the results of the GMEM imaging of 36 selected extragalactic radio sources with a resolution of 0.3-0.5 mas on astrometric and geodetic VLBI observations at 8.2 GHz, obtained with a global array in the period from 1994-1996. In VLBI mapping practice this is the first experience of imaging with such a high resolution using maximum entropy technique. A differential maximum entropy method intended for increasing the dynamic range of images is demonstrated on the radio source 0059+581. In the case of unreliable `closure' phases, completely `phaseless' methods of mapping are recommended. Maps of two sources 0615+820 and 0642+214 are obtained using one such method.Comment: Latex, 11 pages with 4 Postscript figures (images of 36 extragalactic radio sources