Microarcsecond instability of the celestial reference frame

The fluctuation of the angular positions of reference extragalactic radio and optical sources under the influence of the irregular gravitational field of visible Galactic stars is considered. It is shown that these angular fluctuations range from a few up to hundreds of microarcseconds. This leads to a small rotation of the celestial reference frame. The non-diagonal coefficients of the rotation matrix are of the order of a microarcsecond. The temporal variation of these coefficients due to the proper motion of the foreground stars is of the order of one microsecond per 20 years. The celestial reference frame can therefore be considered inertial and homogeneous only to microarcsecond accuracy. Astrometric catalogues with microarcsecond accuracy will be unstable, and must be re-established every 20 years.     

Phototrophic and heterotrophic nano- and microorganisms of sea ice and sub-ice water in Guba Chupa (Chupa Inlet), White Sea, in April 2002

Autotrophic and heterotrophic flagellates, microalgae and ciliates sampled at four stations in the White Sea in April 2002 were studied using epifluorescence microscopy. The concentrations of phototrophic 1.5 μm algae in the middle and lower part of the ice core were very high: up to 6.1 ± 10⁸ cells I⁻¹ and 194 μg C I⁻¹. Heterotrophic algae made up the largest proportion of the nanoplankton (2-20 μm) and microplankton (20-200 μm) at depths 10-25 m below the ice. The proportion of ciliates ranged from about 0.01% to 18% at different stations and depths. Most of the ciliate biomass in the ice was made up of typical littoral zone species, whereas the water under the ice was dominated by phototrophic Myrionecta rubra . Ice algae, mainly flagellates in the upper ice layer and diatoms in the bottom ice layer, supported the proliferation of heterotrophs, algae and ciliates in early spring. Small heterotrophs and diatoms from the ice may provide food for early growth and development of pelagic copepods. Mass development of the ice algae in early spring appears typical for the seasonal ice of the White Sea. Ice algae differ in species composition from the spring pelagic community and develop independently in time and space from the spring phytoplankton bloom.     

Adaptation of the average monthly ionospheric model to current conditions using the data on maximum usable frequencies at two-hop reference radio links

The accuracy in determining the maximum usable frequencies (MUF) of reference radio links has been estimated. A method for using the data on MUF, obtained at two-hop reference radio links, in order to specify the horizontal gradients of electron concentration in the ionosphere has been proposed. The results of the observations at a system of two reference radio links are used to assess the efficiency of such a specification. It has been indicated that the developed method makes it possible to specify the values of the ionospheric critical frequency simultaneously in two radio link regions. The application of two-hop radio links together with one-hop lines substantially broadens the number of reference radio stations that can be used to adapt the parameters of the average monthly ionospheric model to the current conditions.     

Model of the ground ionospheric channel in the problems of communication and position finding

Peculiar specification of the properties of the ionospheric decameter radio channel in the problems of communication and position finding is considered. It is proposed to use the semiempirical model of the ionosphere together with the method of characteristics in order to calculate the signal parameters between emitter and receiver. The errors in determining the vertical angles of arrival, ranges, and signal propagation time in the proposed model and in the ICEPAC model have been compared based on the experimental data.     

Search for gravitational lenses near the extragalactic double object CSL-1

We consider additional arguments in favor of the first observable cosmic string. We discuss candidates for gravitational lensing events near the extragalactic double source CSL-1 (Capodimonte-Sternberg-Lens Candidate no. 1) discovered in the Osservatorio Astronomico di Capodimonte Deep Field (OACDF). The detected excess of candidates for such events cannot be explained in terms of the theory of gravitational lensing by standard extragalactic objects (galaxies, groups of galaxies, etc.) and is in close agreement with the proposed model of gravitational lensing by a cosmic string.     

Principles for selecting a list of reference radio sources for a celestial coordinate system

Time series of the coordinates of radio sources defining the celestial coordinate frame are analyzed. Methods for selecting such sources so as to enhance the stability of the frame are considered. Some of these sources, including so-called “defining” sources, demonstrate significant proper motions. Since the stability of the celestial coordinate frame is determined by an absence of global rotation relative to the defining sources (no net rotation), variation in their coordinates will lead to a rotation of the axes of the celestial coordinate frame. The parameters of this rotation are calculated for two physical models for the motions of extragalactic radio sources. The motions displayed by the first group of sources are linear and uniform. Since the apparent speeds of radio sources are often close to, and sometimes exceed, the speed of light, it is supposed that such radio sources have relativistic jets or plasma clouds that move with speeds roughly equal to the speed of light. The observed uniform, linear motion can then be explained by precession of the jet. The second group of sources display non-linear motions, interpreted as a manifestation of the acceleration of matter by the jet. It is assumed that a cloud of particles that moves into the path of the jet is accelerated to relativistic speeds by the jet. A list of sources that should form a very stable coordinate system for several decades into the future is composed based on these two models.