Latvian Journal of Physics and Technical Sciences, 2012
Radiotelescope RT-32 is a fully steerable 32-m parabolic antenna located at Irbene and belonging ... more Radiotelescope RT-32 is a fully steerable 32-m parabolic antenna located at Irbene and belonging to Ventspils International Radio Astronomy Centre (VIRAC). Currently, the work on upgrading and repair of its receiving hardware and data acquisition systems is of high priority for the VIRAC. One of the main scientific objectives for the VIRAC Radioastronomical observatory is VLBI (very long baseline interferometry) observations in centimetre wavelengths in collaboration with world VLBI networks, such as European VLBI network (EVN), Low Frequency VLBI network (LFVN), and others. During the last years the room in the secondary focus of telescope was reconstructed, and several new receivers were installed. Currently, RT-32 observations are carried out in four different bands: 92 cm, 18 cm, 6 cm, and 2.5 cm. First three of them are already successfully employed in diversified VLBI experiments. The receiver on 2.5 cm band has only one linear polarized chain and is used mainly for the methan...
Plans for geo-VLBI in parallel to astro-VLBI observations at the VIRAC, that could be very nicely... more Plans for geo-VLBI in parallel to astro-VLBI observations at the VIRAC, that could be very nicely connected with geodetic reference network determination tasks.
In order to calculate the molecular concentrations in the interstellar cloud and to obtain heir s... more In order to calculate the molecular concentrations in the interstellar cloud and to obtain heir spatial distribution we have made a computational code to solve the set of equations for chemical equilibrium and equations of charge and atom balance. Now 109 molecules and 1070 chemical reactions are included. Besides, the gas phase reactions with neutrals and ions, formation of molecular hydrogen on grains and the ionization and dissociation due to cosmic rays and UV radiation were taken into account. In order to calculate the photodissociation rates of H2 and CO molecules we take into consideration: i) extinction due to H2 Lyman and Werner series bands, ii) extinction due to atomic H Lyman series lines ? up to n=1 -> n=51, iii) extinction due to 33 CO bands and dust continuum extinction. Only UV continuum for photodissociation of all other species was taken into account.
The question, what is the role of freeze-out of chemical species in determining the molecular abu... more The question, what is the role of freeze-out of chemical species in determining the molecular abundances in the interstellar gas is a matter of debate. We investigate a theoretical case of a dense interstellar molecular cloud core by time-dependent modelling of chemical kinetics, where grain surface reactions deliberately are not included. That means, the gas-phase and solid-phase abundances are influenced by gas reactions, accretion on grains, and desorption, only. We compare the results to a reference model, where no accretion occurs and only gas-phase reactions are included. We can trace that the purely physical processes of molecule accretion and desorption have major chemical consequences on the gas-phase chemistry. The main effect of introduction of the gas-grain interaction is long-term molecule abundance changes that come nowhere near an equilibrium in during the typical lifetime of a prestellar core.
Proceedings of the International Astronomical Union
The deuterium enrichment of many molecules in molecular clouds currently is a topic of intense de... more The deuterium enrichment of many molecules in molecular clouds currently is a topic of intense debate. Theories of molecule deuteration in molecular clouds mostly deal with gas-phase related processes. However, often it is hard to explain the high abundances of multi-deuterated species even when relatively extreme physical conditions are applied. We propose a completely different mechanism of deuteration enrichment - the diffusion of hydrogen in the frozen mantles of interstellar dust grains. This mechanism may be explained as follows. Firstly, many hydrogen-rich molecules are accumulated in a porous grain mantle. Cosmic-ray induced photons dissociate these molecules, producing smaller fragments, including H and H_2. Unlike other species, hydrogen is capable of tunneling right through the amorphous mantle lattice and escaping to surface and gas phases. We argue that this outward diffusion is more important than the inward diffusion into the mantle from the surface. The heavier deute...
Plans for geo-VLBI in parallel to astro-VLBI observations at the VIRAC, that could be very nicely... more Plans for geo-VLBI in parallel to astro-VLBI observations at the VIRAC, that could be very nicely connected with geodetic reference network determination tasks.
Radiotelescope RT-32 is a fully steerable 32-m parabolic antenna located at Irbene and belonging ... more Radiotelescope RT-32 is a fully steerable 32-m parabolic antenna located at Irbene and belonging to Ventspils International Radio Astronomy Centre (VIRAC). Currently, the work on upgrading and repair of its receiving hardware and data acquisition systems is of high priority for the VIRAC. One of the main scientific objectives for the VIRAC Radioastronomical observatory is VLBI (very long baseline interferometry) observations in centimetre wavelengths in collaboration with world VLBI networks, such as European VLBI network (EVN), Low Frequency VLBI network (LFVN), and others. During the last years the room in the secondary focus of telescope was reconstructed, and several new receivers were installed. Currently, RT-32 observations are carried out in four different bands: 92 cm, 18 cm, 6 cm, and 2.5 cm. First three of them are already successfully employed in diversified VLBI experiments. The receiver on 2.5 cm band has only one linear polarized chain and is used mainly for the methan...
Latvian Journal of Physics and Technical Sciences, 2012
Radiotelescope RT-32 is a fully steerable 32-m parabolic antenna located at Irbene and belonging ... more Radiotelescope RT-32 is a fully steerable 32-m parabolic antenna located at Irbene and belonging to Ventspils International Radio Astronomy Centre (VIRAC). Currently, the work on upgrading and repair of its receiving hardware and data acquisition systems is of high priority for the VIRAC. One of the main scientific objectives for the VIRAC Radioastronomical observatory is VLBI (very long baseline interferometry) observations in centimetre wavelengths in collaboration with world VLBI networks, such as European VLBI network (EVN), Low Frequency VLBI network (LFVN), and others. During the last years the room in the secondary focus of telescope was reconstructed, and several new receivers were installed. Currently, RT-32 observations are carried out in four different bands: 92 cm, 18 cm, 6 cm, and 2.5 cm. First three of them are already successfully employed in diversified VLBI experiments. The receiver on 2.5 cm band has only one linear polarized chain and is used mainly for the methan...
Plans for geo-VLBI in parallel to astro-VLBI observations at the VIRAC, that could be very nicely... more Plans for geo-VLBI in parallel to astro-VLBI observations at the VIRAC, that could be very nicely connected with geodetic reference network determination tasks.
In order to calculate the molecular concentrations in the interstellar cloud and to obtain heir s... more In order to calculate the molecular concentrations in the interstellar cloud and to obtain heir spatial distribution we have made a computational code to solve the set of equations for chemical equilibrium and equations of charge and atom balance. Now 109 molecules and 1070 chemical reactions are included. Besides, the gas phase reactions with neutrals and ions, formation of molecular hydrogen on grains and the ionization and dissociation due to cosmic rays and UV radiation were taken into account. In order to calculate the photodissociation rates of H2 and CO molecules we take into consideration: i) extinction due to H2 Lyman and Werner series bands, ii) extinction due to atomic H Lyman series lines ? up to n=1 -> n=51, iii) extinction due to 33 CO bands and dust continuum extinction. Only UV continuum for photodissociation of all other species was taken into account.
The question, what is the role of freeze-out of chemical species in determining the molecular abu... more The question, what is the role of freeze-out of chemical species in determining the molecular abundances in the interstellar gas is a matter of debate. We investigate a theoretical case of a dense interstellar molecular cloud core by time-dependent modelling of chemical kinetics, where grain surface reactions deliberately are not included. That means, the gas-phase and solid-phase abundances are influenced by gas reactions, accretion on grains, and desorption, only. We compare the results to a reference model, where no accretion occurs and only gas-phase reactions are included. We can trace that the purely physical processes of molecule accretion and desorption have major chemical consequences on the gas-phase chemistry. The main effect of introduction of the gas-grain interaction is long-term molecule abundance changes that come nowhere near an equilibrium in during the typical lifetime of a prestellar core.
Proceedings of the International Astronomical Union
The deuterium enrichment of many molecules in molecular clouds currently is a topic of intense de... more The deuterium enrichment of many molecules in molecular clouds currently is a topic of intense debate. Theories of molecule deuteration in molecular clouds mostly deal with gas-phase related processes. However, often it is hard to explain the high abundances of multi-deuterated species even when relatively extreme physical conditions are applied. We propose a completely different mechanism of deuteration enrichment - the diffusion of hydrogen in the frozen mantles of interstellar dust grains. This mechanism may be explained as follows. Firstly, many hydrogen-rich molecules are accumulated in a porous grain mantle. Cosmic-ray induced photons dissociate these molecules, producing smaller fragments, including H and H_2. Unlike other species, hydrogen is capable of tunneling right through the amorphous mantle lattice and escaping to surface and gas phases. We argue that this outward diffusion is more important than the inward diffusion into the mantle from the surface. The heavier deute...
Plans for geo-VLBI in parallel to astro-VLBI observations at the VIRAC, that could be very nicely... more Plans for geo-VLBI in parallel to astro-VLBI observations at the VIRAC, that could be very nicely connected with geodetic reference network determination tasks.
Radiotelescope RT-32 is a fully steerable 32-m parabolic antenna located at Irbene and belonging ... more Radiotelescope RT-32 is a fully steerable 32-m parabolic antenna located at Irbene and belonging to Ventspils International Radio Astronomy Centre (VIRAC). Currently, the work on upgrading and repair of its receiving hardware and data acquisition systems is of high priority for the VIRAC. One of the main scientific objectives for the VIRAC Radioastronomical observatory is VLBI (very long baseline interferometry) observations in centimetre wavelengths in collaboration with world VLBI networks, such as European VLBI network (EVN), Low Frequency VLBI network (LFVN), and others. During the last years the room in the secondary focus of telescope was reconstructed, and several new receivers were installed. Currently, RT-32 observations are carried out in four different bands: 92 cm, 18 cm, 6 cm, and 2.5 cm. First three of them are already successfully employed in diversified VLBI experiments. The receiver on 2.5 cm band has only one linear polarized chain and is used mainly for the methan...
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