Boris Shustov

Molecular Emission Line Formation in Prestellar Cores

We investigate general aspects of molecular line formation under conditions typical of prestellar cores. Focusing on simple linear molecules, we study the formation of their rotational lines with radiative transfer simulations. We present a thermalization diagram to show the effects of collisions and radiation on the level excitation. We construct a detailed scheme (contribution chart) to illustrate the formation of emission-line profiles. This chart can be used as an efficient tool to identify which parts of the cloud contribute to a specific line profile. We show how molecular line characteristics for uniform model clouds depend on hydrogen density, molecular column density, and kinetic temperature. The results are presented in a two-dimensional plane to illustrate mutual effects of the physical factors. We also use a core model with a nonuniform density distribution and chemical stratification to study the effects of cloud contraction and rotation on spectral line maps. We discuss the main issues that should be taken into account when dealing with interpretation and simulation of observed molecular lines.

HIRDES UV spectrographs

The World Space Observatory Ultraviolet (WSO/UV) is a multi-national project grown out of the needs of the astronomical community to have future access to the ultraviolet range of the spectrum. The development of the WSO/UV S/C and the telescope is headed by the Russian Federal Space Agency (Roscosmos). The mission is scheduled to be launched in 2010 into the L2 orbit. The WSO/UV consists of a single Ultraviolet Telescope, incorporating a primary mirror of 1.7 m diameter feeding UV spectrometer and UV imagers. The UV spectrometer comprises three different single spectrographs, two high resolution echelle spectrographs - the High Resolution Double Echelle Spectrograph (HIRDES) - and a low dispersion long slit instrument. Within the HIRDES the spectral band (102 - 310 nm) is separated into two echelle spectrographs covering the UV range between 174- and 310 nm (UVES) and VacuumUV range between 102 and 176 nm (VUVES) with a very high spectral resolution of > 50000. Each spectrograph encompass a stand alone optical bench structure with a fully redundant high speed MCP detector system, the optomechanics and a network of mechanisms with different functionalities. The fundamental technical concept is based on the heritage of the two previous ORFEUS SPAS missions. The phase B1 development activities are described in this paper under consideration of performance aspects, design drivers, the related trade offs (e.g. mechanical concepts, material selection etc.) and the critical functional and environmental test verification approach. Furthermore the actual state of the other scientific instruments of the WSO/UV (e.g. UV imagers) project is described.

A mechanism for the formation of oxygen and iron bimodal radial distribution in the disc of our Galaxy

Recently, it has been proposed that there are two type Ia supernova progenitors: short-lived and long-lived. On the basis of this idea, we develop a theory of a unified mechanism for the formation of the bimodal radial distribution of iron and oxygen in the Galactic disc. The underlying cause for the formation of the fine structure of the radial abundance pattern is the influence of the spiral arms, specifically the combined effect of the corotation resonance and turbulent diffusion. From our modelling, we conclude that in order to explain the bimodal radial distributions simultaneously for oxygen and iron and to obtain approximately equal total iron output from different types of supernovae, the mean ejected iron mass per supernova event should be the same as quoted in the literature if the maximum mass of stars, which eject heavy elements, is 50 M� . For the upper mass limit of 70 M� , the production of iron by a type II supernova explosion should increase by about 1.5 times.

Science with the World Space Observatory - Ultraviolet

The World Space Observatory-Ultraviolet (WSO-UV) will provide access to the UV range during the next decade. The instrumentation on board will allow to carry out high resolution imaging, high sensitivity imaging, high resolution (R~55000) spectroscopy and low resolution (R~2500) long slit spectroscopy. In this contribution, we briefly outline some of the key science issues that WSO-UV will address during its lifetime. Among them, of special interest are: the study of galaxy formation and the intergalactic medium; the astronomical engines; the Milky Way formation and evol ution, and the formation of the Solar System and the atmospheres of extrasolar p lanets.

Instrumentation of the WSO-UV project

Dedicated to spectroscopic and imaging observations of the ultraviolet sky, the World Space Observatory - Ultraviolet mission is a Russian-Spanish collaboration. The project consists of a 1.7m telescope with instrumentation able to perform: a) high resolution (R ≥50 000) spectroscopy by means of two echellé spectrographs covering the 115–310 nm spectral range; b) long slit (1x75 arcsec) low resolution (R ∼ 1000) spectroscopy with a near-UV channel and a far-UV channel to cover the 115–305 nm spectral range; c) near-UV and a far-UV imaging channels covering the 115-320 nm wavelength range; d) slitless spectroscopy with spectral resolution of about 500 in the full 115–320 nm spectral range. Here we present the WSO-UV focal plane instruments, their status of implementation, and the expected performances.

A method for molecular-line radiative-transfer computations and its application to a two-dimensional model for the starless core L1544

We present a numerical method and the URAN(IA) computer code for two-dimensional, axially symmetric radiative-transfer computations in molecular lines and spectral modeling. The algorithm is based on Monte Carlo computations of the mean radiation intensity and Accelerated Λ Iterations (ALI) to provide self-consistency between the radiation field and molecular excitation. The code is applied to the structure and kinematic properties of the starless core L1544, which is often considered to be the collapsing core of a molecular cloud. This object has been well studied, but none of the one-dimensional models obtained earlier has been able to provide a self-consistent picture of its structure and kinematics. We show that the spectral features of L1544 can be reproduced in a two-dimensional model in which the cloud has an axial ratio of 2: 1, a mean velocity of contraction (collapse) of Vr∼50 m/s, and a rotational velocity of up to Vφ ∼ 200 m/s. We construct the model of L1544 based on a continuous transition from an initially homogeneous cloud to the observed configuration. The velocity of the contraction is appreciably lower than is predicted by one-dimensional dynamical models. We discuss the problems of interpreting observed molecular-line profiles and prospects for developing self-consistent models for the chemical and dynamical evolution of molecular clouds.

The WSO: a world-class observatory for the ultraviolet

The World Space Observatory is an unconventional space project proceeding via distributed studies. The present design, verified for feasibility, consists of a 1.7-meter telescope operating at the second Largangian point of the Earth-Sun system. The focal plane instruments consist of three UV spectrometers covering the spectral band from Lyman alpha to the atmospheric cutoff with R~55,000 and offering long-slit capability over the same band with R~1,000. In addition, a number of UV and optical imagers view adjacent fields to that sampled by the spectrometers. Their performance compares well with that of HST/ACS and the spectral capabilities of WSO rival those of HST/COS. The WSO, as presently conceived, will be constructed and operated with the same distributed philosophy. This will allow as many groups and countries to participate, each contributing as much as feasible but allowing multi-national participation. Although designed originally with a conservative approach, the WSO embodies some innovative ideas and will allow a world-class mission to be realized with a moderate budget.

Astronomical aspects of cosmic threats: new problems and approaches to asteroid—comet hazard following the chelyabinsk event of February 15, 2013

A new definition of hazardous celestial bodies (HCBs) is introduced, in which the lower limit of the size of a HCB is reduced to 10 m. A new definition for threatening and collisional orbits of DCBs is introduced. The main astronomical factors that must be taken into account when creating systems for the detection of HCBs are analyzed. The most important of these are the uniformity of the distribution of points (regions) for the appearance of HCBs on the celestial sphere in near-Earth space and the practical limit for the velocity of approach of a HCB of 20 km/s (for 90% of bodies). It is shown that the creation of a system for the nearby detection of asteroids and comets arriving from the daytime sky requires the use of a space-based system. A concept for such a system, in which one or several optical telescopes are placed in the vicinity of the libration point L1 for the Sun—Earth system, is developed. Preliminary plans for such a system, called the System for the Detection of Daytime Asteroids (SDDA), are briefly described.

Interaction of the dark-matter cusp with the baryonic component in disk galaxies

The influence of the formation and evolution of a (disk) galaxy on the matter distribution in the dark-matter halo is considered. Calculations of the evolution of an isolated dark-matter halo were carried out with and without including a baryonic component. N-body simulations (for the dark-matter halo) and gas-dynamical numerical simulations (for the baryonic gas) were used for this analysis. Star formation, feedback, and heating and cooling of the interstellar medium were taken into account in the gas-dynamical calculations. The results of these numerical simulations with high spatial resolution indicate that 1) including the star formation resolves the so-called cusp problem (according to CDMcosmological models, the density distribution in the central regions of the dark-matter halo should have a distinct peak (cusp), which is not shown by observations); 2) the interaction of the dark matter with dynamical substructures of the stellar-gas galactic disk (spiralwaves, a bar) affects the shape of the dark-matter halo. In particular, the calculated dark-matter distribution in the plane of the disk is more symmetric when the baryonic component is taken into account.

The Stellar Epoch in the Evolution of the Galaxy

We consider the astrophysical evolution of the Galaxy over large time scales, from early stages (an age of ∼108 yrs) to the end of traditional stellar evolution (∼1011 yrs). Despite the fact that the basic parameters of our stellar system (such as its size, mass, and general structure) have varied little over this time, variations in the characteristics of stars (their total luminosity, color, mass function, and chemical composition) are rather substantial. The interaction of the Galaxy with other stellar systems becomes an important factor in its evolution 100–1000 Gyr after its origin; however, we take the Galaxy to be isolated. In the model considered, the basic stages of Galactic evolution are as follows. The Galaxy forms as the result of the contraction (collapse) of a protogalactic cloud. The beginning of the Milky Way’s life—the relaxation period, which lasts about 1–2 Gyr—is characterized by active star formation and final structurization. The luminosity and colors of the Galaxy are correlated to the star formation rate (SFR). The young Galaxy intensely radiates high-energy photons, which are mostly absorbed by dust and re-emitted at IR wavelengths. In the subsequent period of steady-state evolution, the gas content in the Galactic disk gradually decreases; accordingly, the SFR decreases, reaching 3–5M⊙/yr at the present epoch and decreasing to 0.03M⊙/yr by an age of 100 Gyr. Essentially all other basic parameters of the Galaxy vary little. Later, the decrease in the SFR accelerates, since the evolution of stars with masses exceeding 0.4M⊙ (i.e., those able to lose matter and renew the supply of interstellar gas) comes to an end. The Galaxy enters a period of “dying”, and becomes fainter and redder. The variation of its chemical composition is manifested most appreciably in a dramatic enrichment of the interstellar gas in iron. The final “stellar epoch” in the life of the Galaxy is completed ∼1013 yrs after its formation, when the evolution of the least massive stars comes to an end. By this time, the supplies of interstellar and intergalactic gas are exhausted, the remaining stars become dark, compact remnants, there is no further formation of new stars, and the Galactic disk no longer radiates. Eventually, infrequent outbursts originating from collisions of stellar remnants in the densest central regions of the Galaxy will remain the only source of emission.