Turbulent diffusion in the interstellar medium

We have calculated the coefficient of turbulent diffusion in a random flow with time restoration, describing the interstellar medium. Such a flow abruptly loses its memory at random times, forming a Poisson flow of events. The coefficient of turbulent diffusion in the flow is determined by the rms velocity and correlation time, as in mixing-length theory, but the numerical coefficient differs from that predicted by this theory. The closure equation derived by us for the transport of the mean concentration of a passive scalar takes a more complicated form than obtained in standard mean-field theory, but the main properties of the equation retain their validity. The possibility of extending the results of this exactly solved problem to the problem of transport in the turbulent interstellar medium is discussed.     

A new exact solution of Kompaneets equation for a shock front

An analytical solution of the Kompaneets equation is found for a medium whose density varies according to a hyperbolic tangent law, from a more diffuse (interstellar) medium to a denser medium (a cloud). The law of motion of the leading points of the shock front is discussed. Intermediate asymptotics describing the acceleration and change of the shape of the shock front are analyzed in detail. The obtained solution can be used to investigate analytically the evolution of the shock-front shape at a boundary with a molecular cloud.     

Chemical composition of gas and grains in dense interstellar clouds

This paper is a short review of the present knowledge on the composition of dense clouds where stars form, with extensions to the less dense interstellar medium and to the most likely sites of grain formation. The problem is complex and intricate, and it is still difficult to answer such fundamental questions as the lifetime of the dense clouds or the lifetime of the interstellar grains.     

Condensation of heavy elements on dust grains in interstellar clouds

A possibility of an efficient condensation of heavy elements, such as iron, on the surface of dust grains in interstellar molecular clouds is studied. A high rate of dust destruction in the interstellar medium from one side, and a high degree of heavy elements depletion from the other indicate that the freezing-out of metals should be efficient in interstellar (predominantly molecular) clouds. This is possible only due to betatron acceleration of dust grains behind shocks that originate under intersection of supersonic turbulent flow. Estimates of the heavy elements depletion due to condensation on the surface of dust grains are given.     

The Photolysis of Aromatic Hydrocarbons Adsorbed on the Surfaces of Cosmic Dust Grains

The results of laboratory mass-spectrometer studies of the laser-induced dissociation of molecules of simple aromatic hydrocarbons adsorbed on a quartz substrate under the conditions of deep vacuum and low temperatures are adapted to the physical and chemical conditions in regions of active star formation in molecular clouds. The main properties of the photolysis of physically adsorbed molecules compared to the photodissociation of isolated molecules in the gas phase are identified. The relevance of molecular photolytic desorption to the real conditions in the interstellar medium is analyzed, in particular, to the conditions in photodissociation regions. It is shown that the photodissociation of adsorbed benzene occurs along other channels and with appreciably lower efficiency than does the corresponding process in the gas phase. The photodissociation of aromatic hydrocarbons adsorbed on the surfaces of interstellar grains cannot make a large contribution to the abundance of hydrocarbons with small numbers of atoms observed in the interstellar medium.

     

Distribution of the relative plasma turbulence level in the galaxy

The statistical dependence of τ/(DM)² (the ratio of the broadening of a pulsar pulse due to scattering in the interstellar medium to the square of the pulsar’s dispersion measure) on the pulsar’s dispersionmeasure, Galactic coordinates, age, and the angular distance to the nearest supernova remnant are studied. This parameter describes the relative level of electron density fluctuations in the turbulent interstellar plasma. It is shown that the interstellar plasma turbulence level is three orders of magnitude higher in the spiral arms of the Galaxy than outside the arms. The plasma turbulence level is approximately an order of magnitude higher in the Galactic arms, in regions within ?0.3° of supernova remnants, than outside these regions. We conclude that the source of energy for the turbulence in the Galactic arms is supernova explosions in the denser medium there.     

Measurement of the inner turbulence scale of the interstellar plasma toward the pulsar PSR B2111+46

The pulsar PSR B2111+46 has been observed at 112 MHz, and a new approach to analyzing pulsar pulses scattered in turbulent interstellar plasma applied. This method is based on the dependence of the normalized energy in the trailing part of a pulse on the intrapulse time. Since the trailing edge of a pulse follow exponential law to high accuracy, the inner turbulence scale of the interstellar plasma exceeds the field coherence scale. The measured scattering parameter is τ _sc = 147 ± 1 ms. Analysis of the parameters of diffractive and refractive scintillations of the pulsar at 610 MHz together with the 112 MHz data shows that the spectrum of the interstellar plasma toward PSR B2111+46 is a piecewise power law: on scales of 10¹³–10¹⁴ cm, the exponent of the turbulence spectrum is n ≃ 4, whereas n = 3.5 on scales of 2 × 10⁸−10¹³ cm. The spectrum flattens with approach to the inner turbulence scale l: n = 3–3.2. The obtained inner turbulence scale is l = (3.5 ± 1.5) × 10⁷ cm. The distribution of the interstellar plasma toward the pulsar is close to statistically homogeneous. The local density (N _e = 0.4 cm⁻³) and filling factor (F = 0.04) of the interstellar plasma have been estimated. The similarity of N _e estimates obtained from the inner scale of the inhomogeneities and the ratio of the emission measure to the dispersion measure provides evidence that the inner turbulence scale corresponds to the ion inertial length.     

The influence of variations of elemental composition on the thermal properties of interstellar gas

The mixing of metals and redistribution of the relative abundances of chemical elements in the interstellar medium often takes place on a timescale that exceeds the characteristic timescales for many other processes, such as ionization and the establishment of thermal equilibrium. Under these conditions, different regions of interstellar gas can have different thermal, chemical, and spectral properties. The paper considers the ionization kinetics and thermal regime of interstellar gas with variations in the relative elemental abundances. The thermal properties and observational (spectral) characteristics are most sensitive to variations of the relative abundance of carbon, oxygen, neon, and iron. The dynamic consequences of such variations are considered.     

The influence of variations of the elemental composition on the thermal properties of gas behind shock fronts

The homogenization of inhomogeneities in the elemental composition of the interstellar medium due to stellar evolution and weak mixing are inevitably related to the action of shocks. This paper considers the influence of variations in the elemental composition on the thermal and ionizational evolution of a collisional gas with the solar metallicity that is cooled behind a shock front with a velocity of 50–120 km/s. The intensities of lines of heavy elements in plasma cooling behind a shock front depend not only on variations in the elemental composition, but also on the shock velocity, due to the different values of the critical density for the transition to the equilibrium level populations in atoms and ions of heavy elements. This circumstance can be used to determine the elemental composition of cool and warm gas of the interstellar medium, as well as the thermal history of the gas.     

Size discontinuity between interstellar and chondritic aromatic structures: A high-resolution transmission electron microscopy study

Polyaromatic hydrocarbons (PAHs) are often considered as abundant and widespread organic structures in the universe and such structures are known to build the macromolecular network of the organic matter in carbonaceous chondrites. Assuming that interstellar PAHs are properly identified from infrared bands, these meteoritic aromatic moieties can be compared with their interstellar counterpart. The main structural parameters of the aromatic units of the insoluble organic matter of the Orgueil and Murchison chondrites are directly determined through high resolution transmission electron microscopy along with image analysis. These aromatic moieties appear weakly organized and of a smaller size than those present in the interstellar medium (containing ∼30 and ∼150 C atoms). Provided chondritic and interstellar polyaromatic hydrocarbons are derived from a similar organosynthesis, the smaller units were selectively preserved in meteorites, likely thanks to their fast accumulation on grains, which would protect them from solar UV photodissociation at the surface of the protosolar disk.     

Spectroscopy of 13 high-mass stars in the Cyg OB2 association

The NES echelle spectrograph of the 6-m telescope of the Special Astrophysical Observatory has been used to obtain high-resolution spectra for 13 hot O3-B4 stars in the Cyg OB2 association, making it possible to study weak spectral features of stellar and interstellar origin. Velocity fields in the atmospheres and interstellar medium, characteristics of optical spectra and line profiles are investigated. The cascade star-formation scheme for the association is confirmed. Evidence is presented suggesting that the hypergiant Cyg OB2 No. 12 is an LBV object and that its anomalous reddening has a circumstellar nature.     

Response of a multicomponent interstellar medium to external gravitational influences

The contribution of cosmic rays as a collection of charged particles to the generation of currents in the interstellar medium and to the total viscosity of this medium is analyzed. Our estimates show that this contribution is negligible under the conditions commonly found in our Galaxy but can become important when an excess dust concentration above the mean level is combined with a local increase in the cosmic-ray density.     

Characteristics of the pulsed emission of the peculiar pulsar B1822-09 at low radio frequencies

The pulse structure of the pulsar B1822-09 has been studied at 112, 62, and 42 MHz. The observations were conducted in 2010 on the Large Scanning Antenna and the DKR-1000 radio telescope of the Pushchino Radio Astronomy Observatory. The shape of the main pulse and interpulse undergo considerable changes at low radio frequencies. In the main pulse, the precursor disappears and is replaced by a new component that trails 50 ms behind the main component. At 62 MHz, the interpulse acquires a pronounced two-peaked shape. At 62 and 112 MHz, as well as at higher frequencies, the brighter second component of the interpulse follows the main pulse at 185° and has a relative amplitude of about 5%. The main pulse width changes with frequency according to the power law W _0.5 ∼ ν ^−0.15 in the frequency range 42–4750-MHz. The interpulse width follows this law only in the range 325–4750 MHz; at 112, 102, and 62 MHz, the interpulse is almost a factor of three broader than themain pulse. The parameters of the pulse’s scattering on interstellar plasma inhomogeneities and the initial pulse width before it enters the scattering medium have been measured at 62 and 42 MHz. The frequency dependence of the characteristic scale for scattering of the pulses of B1822-09 corresponds to a Kolmogorov spectrum for the electron-density fluctuations in the interstellar medium in the direction toward this pulsar.     

A general geomorphological map of Romania on the scale of 1:25,000, Zlatna sheet

All of the General Geomorphological Map of Romania on the medium scale of 1:200,000, with 50 sheets was elaborated in the Institute of Geography during the 1976--1990 period. A new general geomorphological map, this time on a large scale -- 1:25,000 and 1:50,000 -- is being worked out since 1991. The legend of the last two maps lists 250 geomorphological elements, grouped by ten large categories: 1. geological substrate; 2.denudational relief; 3. fluviatile relief; 4. lacustrine and marine relief; 5. glacial and periglacial relief; 6. karst relief; 7. eolian relief; 8. volcanic relief; 9. structural relief and, 10. anthropic relief. The general geomorphological maps of Romania on large scale (1:25,000 and 1:50,000) are accompanied by two auxiliary maps, i.e. a map of relief units and a morphostructural map, as well as by three geomorphological cross-sections. These show, beside landforms and geological structure, also rock composition and inclination of the strata. As an illustration, there is Zlatna sheet, on the scale of 1:25,000, which covers an area situated in the south-eastern part of the Romanian Western Carpathians (Apuseni Mountains). The work expounds on the location, division of the relief, relief energy and landforms, rock structure and make-up, current modelling processes, terraces, minor channel-beds, distribution of volcanic funnels and anthropic relief.     

Circumstellar envelopes of hot stars: Formation of extended regions of weakly ionized gas

We propose a model explaining the presence of vast regions of partially ionized gas in the interstellar medium. The circumstellar envelope of a hot star absorbs soft ionizing radiation, but transmits an appreciable fraction of the hard photons, which are absorbed much more weakly than photons with energies close to the ionization limit. For this reason, the radiation attenuated by the envelope becomes harder, and can penetrate to larger distances. For stars hotter than 50 000 K, the transition zone between the ionized and neutral gas can extend to tens or hundreds of parsecs. Thus, a region of partially ionized hydrogen, with a small gradient of the degree of ionization without a well-defined inner HII zone, can form in the interstellar medium.     

Formation of galactic shocks and the vertical structure of the gaseous disk of the galaxy in a “turbulent” interstellar medium

The effects on the formation of Galactic shocks and the vertical structure of the Galactic disk due to thermal processes in a cloudy interstellar medium as it flows through a spiral density wave in the plane of the Galactic disk are considered. The evolution of the gas is fundamentally different, depending on the thermal properties of the medium. For example, if it is compressed in the horizontal direction (parallel to the Galactic plane) by the gravitational forces of the spiral density waves responsible for the formation of spiral arms, an isothermal and adiabatic medium is swept out in the vertical direction. However, on the contrary, a medium whose volume loss function increases fairly rapidly with density and temperature is further compressed under the action of the overall gravitational field of the galaxy. This effect is referred to as “self-focusing,” and may serve as an additional mechanism to explain the recently discovered anticorrelation between the width of the atomic hydrogen layer in the Galaxy and the gas density. The difference in the vertical behavior of media with different thermal properties can be used as an indicator of the thermal properties of a particular component of the interstellar gas (atomic or molecular). Attention is drawn to the fact that Galactic shocks themselves represent a mechanism that can heat the ensemble of clouds, i.e., increase the dispersion of cloud velocities. The vertical structure of a Galactic shock front is constructed, which is in qualitative agreement with the “bow shock” inferred from radio data.     

辽西地区沟系次生晕测量方法的研究

文章介绍了辽西某多金属矿区沟系次生晕测量的应用及效果,探讨了沟系次生晕测量中布点、采样、元素含量统计、异常图编制、异常解释和异常检查的方法与技术.工作成果证明,沟系次生晕测量是一种针对沟系发育、厚层覆盖地区的快速、经济和有效的化探方法,可迅速圈定矿化带、评价矿化带的含矿性.     

辽西地区沟系次生晕测量方法的研究

文章介绍了辽西某多金属矿区沟系次生晕测量的应用及效果，探讨了沟系次生晕测量中布点、采样、元素含量统计、异常图编制、异常解释和异常检查的方法与技术。工作成果证明，沟系次生晕测量是一种针对沟系发育、厚层覆盖地区的快速、经济和有效的化探方法，可迅速圈定矿化带、评价矿化带的含矿性。     

地球化学数据的定和化及其在系统误差校正中的应用

地球化学数据间的系统误差,既影响了图幅的拼接,又因破坏了多元总体的相关结构而干扰到地球化学数据的统计分析。针对这一问题,这里分析了地球化学数据的定和特点,探讨了系统误差校正的定和化处理方法。同时,结合实例说明了该方法的实际应用效果,并验证了定和化方法的有效性。