Far-infrared contribution to interstellar extinction from graphite whiskers

A mass contribution of graphite whiskers as small as 0.1% to the population of interstellar grains could dramatically change their far-infrared extinction properties. With varying mass fractions of graphite whiskers, and for different size parameters, the infrared extinction could vary from a ^-2 dependence to ⁰, consistent with the requirements of some astronomical observations.     

Evidence for iron whiskers near the galactic centre

It is shown that ~ 10² M of iron in the form of long slender whiskers, expelled from supernovae, can explain an observed deficit of line emission in the 157.7µm C II line and in the 205µm N II line from the galactic centre region.     

Hydrogen and Helium under high pressure: A case for a classical theory of dense matter

When subject to high pressure, H₂ and ³He are expected to undergo phase transitions, and to become metallic at a sufficiently high pressure. Using a semiclassical theory of dense matter proposed by Savi and Kaanin, calculations of phase transition and metallisation pressure have been performed for these two materials. In hydrogen, metallisation occurs at p _M= (3.0 ± 0.2) Mbar, while for helium the corresponding value is p _M= (106 ± 1) Mbar. A phase transition occurs in helium at p _tr= (10.0 ± 0.4) Mbar. These values are close to the results obtainable by more rigorous methods. Possibilities of experimental verification of the calculations are briefly discussed.     

Estimates for the effective electrical conductivity of the core in the interior of Jupiter and Saturn

In the deep interior of the giant planets Jupiter and Saturn, ordinary hydrogen and helium are transformed into a conducting metallic liquid at extremely high pressure. It is likely that the giant planets' observed magnetic field is constantly generated in the metallic fluid core by magnetohydrodynamic processes, converting mechanic energy in the form of convection into magnetic energy. The maximum strength of their magnetic fields is likely to be limited by magnetic field instabilities which convert the magnetic energy back into convection. The parameter which governs the occurrence of magnetic instabilities is the Elsasser number, = B ²/2, where B is the field strength, is the electrical conductivity, is the rotation rate and is the density. Since magnetic instability will be very active when exceeds a critical value _c 10 (the precise value depending on the magnetic field distribution), this imposes an upper bound on the effective electrical conductivity of the metallic fluid which comprises the bulk of Jupiter's interior and much of Saturn's.Stability calculations including both toroidal (model) and poloidal (observed) components of the magnetic field in a rapidly rotating spherical shell, have been performed. The most stable configuration of the field is when the poloidal component of field is strong and the toroidal field is weak; in this case we obtain an upper bound for electrical conductivity of 3 × 10⁶ S/m; while the most unstable configuration of the field is when the toroidal and poloidal fields are comparable, giving rise to _m 3 × 10⁵ S/m. The implications of the results for general dynamo theory are also discussed.     

Physical characters of HD 93044

The measurements ofuvby H of HD 93044 were obtained in April 1991, and the observational results that the star locates nearly in the middle of Scuti instability strip with somewhat deviation to red edge. According to Crawford (1979) and Philip's (1979) calibrations, the effective temperature, absolute visual magnitude and surface gravity are obtained to beT _eff = 7300±200 K,M _v = 1.^m33±0.39 and logg = 3.7±0.15, respectively. The observational results of _m1 = 0.01 give an estimate of [Fe/H] = –0.003 ± 0.18, so the opinion of metallic deficient is not supported obviously. The observations show the reddening indexE(b -y) to be 0.014 which is 1.4 times as large as the standard deviation of Crawford's (1979) statistics.Project supported by Young Foundation of Beijing Astronomical Observatory, China     

Franck-condon factors and -centroids for certain band systems of astrophysical molecular ions CN+ and N+2

The Franck-Condon factors and r-centroids, which are very closelyrelated to relative vibrational transition probabilities, have beenevaluated by the more reliable numerical integration procedure forthe bands of c ¹ - a ¹ and f ¹ - a ¹ systems of CN ⁺ and C ^{2 +} _u- X ^{2 +} _g and D ² _g- A ² _u systems of N ⁺ ₂ molecular ions of astrophysical interest,using a suitable potential.     

Lunar rock magnetism

The relationship between the magnetization and temperature in a high constant magnetic field for a temperature range between 5 K and 1100 K was examined for Apollo 11, 12 and 14 lunar materials. The average value of Curie point temperature is (768.2 ± 3.5)°C for the lunar igneous rocks and (762.5 ± 3.4)°C for the lunar fines and breccias. A tentative conclusion about the ferromagnetic substance in the lunar materials would be that Fe is absolutely dominant with a slight association of Ni and Co, and probably Si also, in the lunar native irons.The antiferromagnetic phase of ilmenite and the paramagnetic phase of pyroxenes are considerably abundant in all lunar materials. However, a discrepancy of observed magnetization from a simulated value based on known magnetic elements for the temperature range between 10 and 40 K suggests that pyroxene phase represented by (M _x Fe_1-x ) SiO₃ (whereM = Ca²⁺, Mg²⁺, etc and 0 x 1/4) also may behave antiferromagnetically.Magnetic hysteresis curves are obtained at 5 K and 300 K, and the viscous magnetic properties also are examined for a number of lunar materials. The superparamagnetically viscous magnetization has been experimentally proven as due to fine grains of metallic iron less than 200 Å in mean diameter. The viscous magnetization is dominant in the lunar fines and breccias which is classified into Type II, while it is much smaller than the stable magnetic component in lunar igneous rocks (Type I). The superparamagnetically fine particles of metallic iron are mostly blocked at 5 K in temperature; thus coercive force (H _c ) and saturation remanent magnetization (I _R ) become much large at 5 K as compared with the corresponding values at 300 K.Strongly impact-metamorphosed parts of lunar breccias have an extremely stable NRM which could be attributed to TRM. NRM of the lunar igneous rocks and majority of breccias (or clastic rocks) are intermediately stable, but their stability is considerably higher than that of IRM of the same intensity. This result may imply that some mechanism which causes an appreciable magnitude of NRM and the higher stability, such as the shock effect, may take place on the lunar surface in addition to TRM mechanism for special cases.A particular igneous rock (Sample 14053) is found to have an unusually strong magnetism owing to a high content of metallic iron (about 1 weight percent), and its NRM amounts to 2 × 10^–3 emu/g. The abundance of such highly magnetic rocks is not known as yet but it seems that the observed magnetic anomalies on the lunar surface could be related to such highly magnetized rock masses.     

Detection of CH3D on Titan

We report the detection of ¹³CH₃D in Titan's stratosphere from Cassini/CIRS infrared spectra near 8.7 μm. Fitting simultaneously the ν₆ bands of both ¹³CH₃D and ¹²CH₃D and the ν₄ band of CH₄, we derive a D/H ratio equal to and a ¹²C/¹³C ratio in deuterated methane of , consistent with that measured in normal methane.     

Quantum effects in cyclotron plasma absorption

It is shown that X-ray radiation of neutron stars with magnetic fieldsB=10¹¹–10¹³ G near cyclotron resonances=s _B (s=1,2,...) is deeply affected by such quantum effects as electron-positron vacuum polarization (significant at V=3×10²⁸ n _e ^–1 (B/B _C ⁴)1, whereB _C =4.4×10¹³G), the quantizing character of the magnetic field (significant atV=3 x 10²⁸ n _e ^–1 (B/B _c)⁴1 whereB _c =4.4 x 10¹³G), the non-harmonic character of the Landau levels, and the quantum recoil of electrons. The latter two factors shift the resonances by the frequency –s ² _B (B/2B _c )sin², being the angle between the direction of radiation propagation and the magnetic field. IfVV ₀ (for 1,V ₀^–1=(mc ²/2T)^1/2), the normal mode (NM) polarizations, as well as the absorption coefficientk ₁ of the extraordinary NM in the Doppler core of the first resonance (|–| _B cos ), is only slightly affected by varyingb and/orV, whereas for the ordinary NM (at 1)k ₂k ₁ ²[b + (3 + tan²–2V)²]k ₁. For sufficiently largeb and/orV the quantum effects amplify resonant absorption of the ordinary NM at _B , with spin-flip transitions playing a major role atb1+V ². IfVV ₀, the coefficientsk ₁ andk ₂ in the Doppler core of the resonance are of the same order and acquire some peculiar features (shifts, intersections, etc.), with the NM polarizations depending sharply on and being strongly non-orthogonal. AtVV ₀,k ₂=k ₁(cos² +B/2B _C ) and the polarizations are almost linear. Near high resonances (s2), as a rule,k _1,2(1 + b) ^{s–1 2s–3} i.e., absorption increases withb due to replacement of the thermal energy of the transverse motion of electron,T, by the magnetic energy _B . The above effects should be taken into account for an interpretation of observational data on X-ray pulsars (e.g., Her X-1) and other X-ray sources associated with neutron stars.     

On the excitation of lower levels of singlet helium in quiescent prominences

The paper deals with the excitation of the helium singlet level 2¹ P in the homogeneous and filamentary models of quiescent prominences with following parameters: the optical thickness at the limit of helium Lyman continuum _1c ^M = 0.1–100, T _e = 7000 K, n _e = 5 × 10¹⁰ cm^–3. Assuming a model He atom with seven discrete levels (1¹ S, 2³ S, 2¹ S, 2³ P, 2¹ P, 3³ D, 3¹ D) and the continuum the steady state equations for the levels 2³ S, 2¹ P and the continuum have been solved together with the radiative transfer equations for the line 584 Å and the continuum 504 Å. The variations with depth of the functions n ₂ ³ _S /n ₁ ¹ _S (₁ c), n ₂ ¹ _P /n ₁ ¹ _S (_1c ), and n ⁺ _He n _e /n ₁ ¹ S(_1c ) as well as the intensities of the triplet (D₃, 10830 Å) and singlet (16678, 20581 Å) lines have been calculated. Comparison with observations leads to the following conclusions: (1) The line intensities calculated for filamentary models of prominences agree better with observations than those for homogeneous ones. (2) The helium level 2¹ P is excited by diffuse field 584 Å being formed by recombinations and spontaneous transitions 2¹ P – 1¹ S and escaping from the prominence into the space between the filaments and to the surface. (3) Underpopulation of the singlet level 2¹ P may be explained by combination of weak excitation mechanism (recombinations and formation of the diffuse field 584 Å) and strong deexcitation mechanism (spontaneous transitions into the level 1¹ S).     

Effects of mass transfer on the unsteady free convection flow past an accelerated vertical porous plate with variable suction

An exact analysis of the effects of mass transfer on the flow of a viscous incompressible fluid past an uniformly accelerated vertical porous and non-porous plate has been presented on taking into account the free convection currents. The results are discussed with the effects of the Grashof number Gr, the modified Grashof number Sc, the Schmidt number Sc, and the suction parametera for Pr (the Prandtl number)=0.71 representating air at 20°C.Nomenclature a suction parameter - C species concentration - C species concentration at the free stream - g acceleration due gravity - Gc modified Grashof number (vg^*(C –C )/U ₀ ³ ) - Pr Prandtl number (C _p/K) - T temperature of the fluid near the plate - T dimensionless temperature near the plate ((T-T )/(T -T )) - U(t) dimensionless velocity of the plate (U/U ₀) - v normal velocity component - v ₀ suction/injection velocity - x, y coordinate along and normal to the plate - v kinematic viscosity (/gr) - C _p specific heat at constant pressure - C _w species concentration at the plate - C non-dimensional species concentration ((C-C )/(C _w -C )) - Gr Grashof number (g(T _w -T )/U ₀ ³ ) - D chemical molecular diffusivity - K thermal conductivity - Sc Schmidt number (/D) - T _w temperature of the plate - T free stream temperature - t time variable - t dimensionless time (tU ₀ ² /) - U ₀ reference velocity - u velocity of the fluid near the plate - u non-dimensional velocity (u/U ₀) - v dimensionless velocity (v/U ₀) - v ₀ non-dimensionalv ₀ (v ₀ /U₀)=–at^–1/2 - y dimensionless ordinate (yU ₀/) - density of the fluid - coefficient of viscosity     

Some characteristic magnetic properties of lunar materials

One of the typical magnetic characteristics of lunar materials is the composition of their ferromagnetic constituent. Lunar breccias often contain kamacite (less than 7 weight per cent of Ni content) as well as almost pure metallic iron. Metallic ferromagnetics in most igneous rocks are almost pure iron, but the kamacite phase also has been found in some Apollo 15 igneous rocks. It seems likely therefore the metallic ferromagnetics in the lunar crust are more or less similar to those in chondrites.Another typical magnetic characteristic of lunar materials is the presence of a considerable amount of superparamagnetically fine particles of metallic iron. A higher relative content of such fine iron particles results in a higher value of the ratio of magnetic susceptibility (o) to saturation magnetization (I _s), a smaller ratio of the coercive force (H _c) to remanence coercive force (H _RC), and an extremely higher ratio of the viscous component (I _v) to the stable one (I _s) of the remanent magnetization.Communication presented at the Lunar Science Institute Conference on Geophysical and Geochemical Exploration of the Moon and Planets, January 10–12, 1973.     

Cylindrical oscillations of force-free electromagnetic fields

This paper is devoted to Force-Free Electromagnetic Oscillations in a constant magnetic field. A correction is made in the derivation of the basic equation. The paper confirms the predicted spectrum of frequencies, namely _n = _o (n + 1)^1/2;n = 0, 1, 2, .... In addition it is suggested that hybrid frequency _n = ( _n ² + _H ² )^1/2 should be found in observational data.     

An Improved Optical Model for the Non-LTE Problem for the CO2 Molecule in the Atmosphere of Mars: Nighttime Populations of Vibrational States and the Rate of Radiative Cooling of the Atmosphere

The estimates of the population of excited vibrational states of the CO₂ molecule and of the rate of radiative cooling of the atmosphere in the 15-m CO₂ band are given for the nighttime mesosphere and thermosphere of Mars. For the first time, these estimates are made (1) with allowance for the overlap of lines in the 15-m band; (2) for a wide set of vibrational states of seven isotopes of the CO₂ molecule, which was used earlier in the solution of a similar terrestrial problem; and (3) using the rate constant for quenching of the CO₂(01¹0) state in collisions with oxygen atoms, which has been recently measured for low temperatures by Khvorostovskaya et al. (2002). The main results are as follows. 1. The approximation of isolated lines provides a satisfactory accuracy of determining the radiative cooling rate and overestimates vibrational temperatures of the states of the ₂ mode by no more than 3 K for the ¹²C¹⁶O₂ molecule and by no more than 2 K for low-abundant isotopes of the CO₂ molecule. 2. A reasonably high accuracy of estimating the cooling rate can be achieved by taking into account only fundamental vibrational transitions in ¹²C¹⁶O₂, ¹³C¹⁶O₂, ¹⁶O¹²C¹⁸O, and ¹⁶O¹²C¹⁷O molecules and the hot transitions 2_{2 2} and 3₂ 2₂ in the ¹²C¹⁶O₂ molecule. 3. The vertical profile of the total rate of radiative cooling displays two peaks. The maximum near a height of 130 km is very sensitive to temperature and to the ratio of the mixture for oxygen in the atmosphere.     

Unexplained empirical relations among certain scatterings

When the differential cross-section data of ⁺ -proton scattering are compared to the data of proton-alpha scattering at momenta related by 4p₄=p (where p₄ is the momentum of p-alpha scattering and p is the momentum of ⁺ -proton scattering) a correlation is observed between p=125 MeV/c and 1100 MeV/c. The correlation is most pronounced in the region of the lowest energy resonance of both scatterings (p210 MeV/c). A less pronounced correlation (in the lower energy regions) among four scatterings is observed when the differential cross-section data of ⁺ -p and p-alpha scatterings and the data of p-³He and protondeuteron scatterings are compared using relations 4p₄=3p₃=2p₂=p (where p₃ is the p-³He momentum and p₂ is the proton-deuteron momentum). The facts strongly suggest something of physical significance but no theoretical explanation is known. Indeed, an explanation seems to be beyond the scope of existing theory.     

Plasmon neutrinos emission in a strong magnetic field

The decay of a longitudinal plasmon into two neutrinos is studied in the presence of a strong magnetic field. Contrary to the transverse case, for longitudinal plasmons the existence of a new mode, entirely dependent on the magnetic field, greatly enhances the energy loss at high densities. Denoting byQ _HandQ ₀the neutrino energy losses with and without magnetic field respectively, the situation is as follows: atH10¹¹ G andT10⁹K,Q ₀10⁵ Q _Hfor <10¹¹g cm^–3, WhileQ _H10¹⁰ Q ₀for >10¹¹g cm^–3. A second physically interesting feature is the anisotropic character of the energy loss which is highly peaked along the field lines, giving rise to a shorter cooling time in that direction than in any other.     

Grain formation in the expanding gas flow around cool luminous stars

We studied grain formation process and flow structure around cool luminous mass-loss stars. The nucleation and growth theory of Yamamoto and Hasegawa was extended to the case of expanding gas flow.The envelope was assumed to be steady, spherically symmetric, in thermal and radiative equilibrium, optically thin, and driven by radiation pressure on grains. For oxygen rich stars, Mg-silicate was found to be the first condensate which can drive the gas effectively. The following stellar parameters were chosen; stellar massM _*=1M , effective temperatureT _*=3000K, stellar luminosityL _* from 7.5×10³ to 2.0×10⁴ L , and mass-loss rate |M| from 1.0×10^–6 to 1.0×10^–4 M yr^–1.Main results of calculations are as follows; (1) grain condensation temperatureT _c9801080 K; (2) total gas pressure at the condensation pointP _t6×10^–116×10^–9 atm; (3) scale parameterA _c10³6×10⁴; and (4) final grain sizer _f=400Å1m. For the smaller |M| or the largerL _*, these values are the smaller. We recognized two types of flow solutions (1) Dust driven flow for large |M|, which reaches the sonic point near the condensation point; and (2) Modified Parker flow for small |M| for which grain sizer _f is almost independent of |M|.A comparison with observational results ofL _* and gas terminal velocityV suggests that Mg-silicate grains are of submicron size, which are effective for interstellar extinction in visible and infrared. Fe-grains condense in the rarefied outflow with a size probably smaller than 100Å, which may contribute for interstellar ultraviolet extinction. The envelope has three-layer structure inner dense region with small outflow velocity, grain formation layer and outer rarefied region with fast outflow velocity.No flow solutions exist forM _* greater than a critical stellar massM _*cr for a given stellar luminosityL _* and mass-loss rate |M|.For example, critical stellar massM _*cr=1.8M forL _*=10⁴ L ,T _*=3000 K, and |M|=10^-5 M yr^-1.     

Spatial and Temporal Behavior of a Laser Generated Titanium Plasma

Optical emission studies have been performed on the laser ablation of Titanium metallic targets. The high intensity radiation of a pulsed N₂ laser (337.1 nm; 8 J/cm²) was focused onto the target to generate a short living (150 ns) plasma cloud that expands away from the surface into vacuum at high velocities. Time resolved measurements were taken as a function of the distance from the studied surface with a spatial rsolution of 20 µm, by collecting the emitted light in a direction perpendicular to the plasma expansion axis. A simple diffusion model with a source term is proposed to demonstrate the interaction of the laser beam with the plasma plume, as derived from analysis of the space-time behavior of several UV and visible atomic transitions.     

VR c photometry of dwarf cepheids (I)

In this paper, we present VRc photometric observations of four dwarf cepheids: YZ Boo (P = 0 _. ^d 104, V = 0 _. ^m 5), AD CMi (P = 0 _. ^d 123, V = 0 _. ^m 5), XX Cyg (P = 0 _. ^d 135, V = 0 _. ^m 5), EH Lib (P = 0 _. ^d 088, V = 0 _. ^m 7). The light curves were obtained at West Mountain Observatory, Provo, Utah on 14 nights from 1983 through 1986 and contain 589 data points in each of theV andR bands in the Cousin photometric system. A detailed study of these stars, based on the present light curves, will be published separately.     

Generation of acoustic and gravity waves by turbulence in an isothermal stratified atmosphere

Lighthill's method of calculating the aerodynamic emission of sound waves in a homogeneous atmosphere is extended to calculate the acoustic and gravity-wave emission by turbulent motions in a stratified atmosphere. The acoustic power output is P _ac 10³ _o u _o ³ /l _o M ⁵ ergs/cm³ sec, and the upward gravity wave flux is F _zgr 10² _o U _o ³ /l _o (l _o ergs/cm³ sec. Here u ₀ is the turbulence velocity scale, l ₀ is its length scale, and H the scale height at the atmosphere. M = u ₀/c ₀ is the Mach number of the turbulence. The acoustic power output is proportional to the maximum value of the turbulence spectrum, and inversely to its rate of falloff at high frequencies. The stratification cuts off the acoustic emission at low Mach numbers. The gravity emission occurs near the critical angle to the vertical _c = cos^–1 / ₂, where ₂ ² = ( - 1)/ ² (c ₀/H), and at very short wavelengths. It is proportional to the large wave number tail of the turbulence spectrum. On the sun, gravity-wave emission is much more efficient than acoustic, but can occur only from turbulent motions in stable regions, whereas acoustic waves are produced by turbulence in the convection zone.