Observations of interstellar HOCO+: abundance enhancements toward the galactic center

A survey of the 4(04)-3(03) and 1(01)-0(00) transitions of HOCO+ has been made toward several molecular clouds. The HOCO+ molecule was not observed in any sources except Sgr B2 and Sgr A. The 5(05)-4(04) and 4(14)-3(13) transitions were also detected toward Sgr B2. The results indicate that gas phase CO2 is not a major carbon reservoir in typical molecular clouds. In Sgr B2, the HOCO+ antenna temperature exhibits a peak approximately 2' north of the Sgr B2 central position (Sgr B2[M]) and the 4(04)-3(03) line emission is extended over a approximately 10' x 10' region. The column density of HOCO+ at the northern peak in Sgr B2 is approximately 3 x 10(14) cm-2, and the fractional abundance relative to H2 > or = 3 x 10(-10), which is about 2 orders of magnitude greater than recent predictions of quiescent cloud ion-molecule chemistry.     

Identification of the interstellar cyanomethyl radical (CH2CN) in the molecular clouds TMC-1 and Sagittarius B2

We report the astronomical identification of the cyanomethyl radical, CH2CN, the heaviest nonlinear molecular radical to be identified in interstellar clouds. The complex fine and hyperfine structures of the lowest rotational transitions at about 20.12 and 40.24 GHz are resolved in TMC-1, where the abundance appears to be about 5 x 10(-9) relative to that of H2. This is significantly greater than the observed abundance of CH3CN (methyl cyanide) in TMC-1. In Sgr B2 the hyperfine structure is blended in the higher frequency transitions at 40, 80, and 100 GHz, although the spin-rotation doubling is clearly evident. Preliminary searches in other sources indicate that the distribution of CH2CN is similar to that for such carbon chain species as HC3N or C4H.     

Heterodyne spectroscopy of the 158 micron C II line in M42

We have obtained velocity-resolved spectra of the 12C II 157.8 microns 2P3/2-2P1/2 fine structure line in the M42 region of Orion. Observations at 0.8 km s-1 resolution with a laser heterodyne spectrometer show multiple velocity components in some locations, with typical linewidths of 3-5 km s-1. Spectra of theta 1C and BN-KL also show weak emission from the F = 2-1 hyperfine component of the equivalent 13C II line. From the observed 12C II/13C II line intensity ratios, we deduce that the 12C II emission is optically thick with tau approximately 5 at both positions. Excitation temperatures of 128 K and 90 K, together with column densities of approximately 1 x 10(19) cm-2 and approximately 4 x 10(18) cm-2, are derived for theta 1C and BN-KL, respectively.     

Union republic migration trends in the USSR during the 1980s

"This article examines union republic migration trends in the USSR between 1979 and 1987 and prospects for indigenous out-migration from rural areas in Central Asia. The study is based on migration data derived by the residual technique and migration data from the 1985 microcensus. Results indicate that a south-to-north and probably Russian-dominated migration trend emerged in the 1980s, one which marks an almost complete reversal from earlier periods, especially 1959-70. Although Central Asia continues to have low levels of indigenous out-migration, labor surpluses and relatively waning capital investment in Central Asia may change this situation."     

A new approach to the possibilities of Σ(D)-dependence and distances of the supernova remnants

A new way of choosing of the calibrators for constructing (D)-dependence of supernova remnants (SNR) is suggested. A knowledge of the distance of an SNR is not sufficient to consider it as a calibrator. It is shown that neither more accurate determination of distance to calibrators, nor an increase in their number, nor an increase in the precision of the remnant angular size and radio flux determination can lead to a considerable improvement of simple (D)-dependence which is suggested in the given work.For remnants with small surface brightnesses there is no (D)-dependence at all. The most accurate remnant distances currently known, are given: these are liable to change only after a large amount of additional observational data accurately compiled.     

Dynamical effects of dark matter in systems of galaxies

SeveralN-body experiments were performed in order to simulate the dynamical behaviour of systems of galaxies gravitationally dominated by a massive dark background.We discuss mass estimates from the dynamics of the luminous component (M _VT) under the influence of such a background, assuming a constant dark/luminous mass ratio (M _D/M _L) and plausible physical conditions. We extend in this way previous studies (Smith, 1980, 1984) about the dependence ofM _VT on the relative distributions of dark and luminous matter (Limber, 1959). We found that the observed ratio of the virial theorem mass to luminosity (M _VT/L) in systems of galaxies of different sizes could be the result of different stages of their post-virialisation evolution as was previously suggested by White and Rees (1978) and Barnes (1983). This evolution is mainly the result of the dynamical friction that dark matter exerts on the luminous component. Thus our results give support to the idea that compact groups of galaxies are dynamically more evolved than large clusters, which is expected from the hierarchical clustering picture for the formation of such structures.     

Evolution of galaxies: One-zone model with a birth-rate stellar function depending on gas density and temperature

In this paper closed one-zone models with a birth-rate stellar function depending on gas density and temperature are built up, in order to make a zeroth order approximation of thermo-chemical evolution of galaxies. To get a more realistic picture, the models are allowed first to expand with the universe and then to contract according to three successive time-scales, in order to simulate violent relaxation, rapid contraction, and slow contraction processes.Star formation occurs according to a birth-rate (m, t) _g ⁿ T ^r m ^p ( _g , gas density;T, gas temperature; andm, star mass), which reproduces the usual Schmidt-type law in the limitr0. Further we suppose that synthesized metals and helium are instantaneously mixed when returned to gas component at star death, and that relative metal abundances are time-independent: ( any element heavier than He, ). An energy fraction of each typical supernova event is assumed to heat interstellar medium, which is also though always to maintain a steady state.Under these hypotheses it becomes possible to use the interstellar cooling function of Dalgarno and McCray (1972), which is related to a special cosmic abundance of elements, to express analytically an interstellar cooling function related to any abundance. At this stage, numerical computations are performed up to about 12 Gy and the results analyzed in order to reproduce some morphological features observed in the galaxy, namely: (i) the extreme scarcity of stars with nearly zero metal content; (ii) the metal content and mass fraction of halo stars; (iii) the metal content and mass fraction of disk stars; and (iv) the ratio of the present-day birth-rate to the past birth-rate averaged over the age of the disk. It is found that a whole class of theoretical models exist, with slope of the mass spectrum between –2.5 and –2.6, which range from a Schmidt's law limitn=1.3 andr=0 to the opposite limitn=0 andr=–1.2, and are able to fit more or less at the same extent the observations mentioned above. On the analysis of further computations, it is also shown that an universal birth-rate stellar function is in contradiction with neither a dynamical hystory starting from the initial expansion of proto-galaxies, nor a morphological sequence where the amount of angular momentum is the only free parameter for any given mass, at least for what concerns spiral types. Finally, possible refinements for future work are briefly outlined.     

Discrete Alfvén waves in planar flux tubes

Properties of discrete Alfvén wave modes are derived, at frequencies up to the ion-cyclotron frequency, for current-carrying plasma slabs with non-uniform densities. It is shown that the essential features of the dispersion relations can be derived by examining the dominant terms in the potential function, when the wave equation is cast in the Schrödinger equation form. Analytical predictions for a class of mass and current density profiles are compared with numerically calculated dispersion relations and wavefields for particular profiles.     

Bipolar nebulae and jets from young stars: Contributions from calar alto

The topic is reviewed with emphasis on observations in the optical and near infrared spectral range.Paper presented at a Workshop on The Role of Dust in Dense Regions of Interstellar Matter, held at Georgenthal, G.D.R., in March 1986.     

Main sequence for rotating stars of intermediate mass

We have investigated the evolutionary behaviour of intermediate mass (2, 3, 4, 5, and 7M ) Population I stars, assuming two different rates of rotation at the threshold of stability.In the first part of the study, stars are assumed to start with a critical rotation (fast rotation model) and to progress to the point of rotational instability. The stars evolve by losing mass and become rotationally unstable before they reach the zero-age Main Sequence. It is argued that multiple star systems might be formed through the evolution of rapidly rotating stars. An expression for the rotational mass loss rate is derived as a function of the physical parameters of stars.In the second part of the study, stars are assumed to rotate at a rate below the critical value (slow rotation model). The evolution of slowly rotating stars is followed as far as zero-age Main Sequence on the theoretical Hertzsprung-Russell diagram and compared with that of normal stars. The evolutionary paths are found to be more or less similar to those of normal stars; but their positions on the Main Sequence are characterized by effective temperatures and luminosities lower than those of normal stars. The zero-age Main-Sequence times of these stars are longer than those of normal stars. The rotational rates obtained for the zero-age Main Sequence are in good agreement with observed values.