Preliminary calibration results of VEGA 1 and 2 SIGMA-3 gas chromatograph

SIGMA - 3 gas chromatograph on board VEGA 1 and 2 landing probes has been operated successfully in the 60 - 50 km altitude range, providing several in - situ chemical analysis of the gas and the aerosols of Venus cloud layers. Post flight calibration required to derive atmospheric abundancies from gas chromatograms were carried out using the SIGMA - 3 spare model. A Venus atmospheric aerosol simulation chamber was used in which sulfuric acid droplets were generated. Preliminary results of these calibration experiments indicate that the concentration of sulfuric acid in the upper part of the clouds ( 60 to 55 km) is about 1 mg/m³ and suggest that an additional constituant must be present in noticeable amount in the aerosols. From these experiments the mixing ratio upper limits of SO₂ is 100 ppmV and of H₂S and COS is few 10 ppmV.     

S3 and S4 absorption cross sections in the range of 340 to 600 nm and evaluation of the S3 abundance in the lower atmosphere of Venus

S₃ absorption cross section equals 6×10⁻¹⁷ cm² at 400 nm, 6 × 10⁻¹⁹ cm² at 500 nm (less by a factor of 4 than that given by Sanko), 4×10⁻²⁰ cm² at 600 nm. That of S₄ equals 1.5 × 10⁻¹⁷ cm² at 450 nm, 8 × 10⁻¹⁷ cm² at 500 nm, and 4.7 × 10⁻¹⁷ cm² at 600 nm. Preliminary evaluation of the S₃ mixing ratio in the lower atmosphere of Venus is (8±3)×10⁻¹¹ at 5 to 25km according to the Venera 14 measurements and several times lower at the locations of the Veneras-11 and -13.     

Experimental limit on low energy antiprotons in the cosmic radiation

We report results from the Low Energy Antiproton Experiment (LEAP), a balloon-borne instrument which was flown in August, 1987. We find no evidence of antiproton fluxes in the kinetic energy range 120 MeV to 360 MeV, top of the atmosphere. The 90 percent confidence upper limit on the antiproton/proton ratio in this energy range is 3.5 × 10⁻⁵. In particular, this new experiment places an upper limit on the flux almost an order of magnitude below the reported flux of Buffington et al.     

Geminga pulsar observations with gamma-telescope Gamma-1

The Geminga light curve obtained with the “Gamma-1” telescope features two peaks separated by 0.5 ± 0.03 period. The light curve is pronounced for γ-quanta energies higher than 400 MeV. The pulsed flux upper limit (1σ) in the energy interval 50 – 300 MeV is 6·10⁻⁷ cm⁻²sec⁻¹. For energies >300 MeV the pulsed component power law spectrum has an exponent 1.1 _−0.3^+1.1 and an integral flux (1.1±0.3)·10⁻⁶ cm⁻²sec⁻¹.     

Neutral upper atmospheres of Venus and Mars

Numerous measurements of the neutral upper atmosphere above 100 km have been made from spacecraft over Venus and over Mars. The Venus exospheric temperatures are unexpectedly low (less than 300°K near noon and less than 130°K near midnight). These very low temperatures may be partially caused by collisional excitation of CO₂ vibrational states by atomic oxygen and partially by eddy cooling. The Venus atmosphere is unexpectedly insensitive to solar EUV variability. On the other hand, the Martian dayside exospheric temperature varies from 150°K to 400°K over the 11-year solar cycle, where CO₂ 15-μm cooling may be less effective because of lower atomic oxygen mixing ratios. On Venus, temperature increases with altitude on the dayside (thermosphere), but decreases with altitude from 100 to 150 km on the nightside (cryosphere). However, dayside Martian temperatures near solar minimum for maximum planet-sun distance and low solar activity are essentially isothermal from 40 km to 200 km. During high solar activity, the thermospheric temperatures of Mars sharply increase. The Venus neutral upper atmosphere contains CO₂, O, CO, C, N₂, N, He, H, D and hot nonthermal H, O, C, and N, while the dayside Mars neutral upper atmosphere contains CO₂, O, O₂, CO, C, N₂, He, H, and Ar. There is evidence on Venus for inhibited day-to-night transport as well as superrotation of the upper atmosphere. Both atmospheres have substantial wave activity. Various theoretical models used to interpret the planetary atmospheric data are discussed.     

Venera-15 and -16 spacecraft: Images and maps of Venus

The main purpose of the spacecraft Venera-15 and -16 was to radar map the north hemisphere of Venus. From October 1983 to July 1984, when this experiment was conducted, an area of 115 million km² was mapped. It stretches from the north pole to the latitude of 30°. The images (radar swathes) and height profiles of the whole surveyed territory were constructed.

At present mosaic maps of Venus were drawn by computer combining of individual swathes in a certain map projection. The height of the local topography was taken into consideration. Topographic maps of Venus were also drawn by interpolation of individual height profiles. They are the most detailed maps of Venus available.     

An archival study of extended X-ray emission from classical and recurrent novae

I discuss morphology and spectrum of the first resolved and detected classical nova shell in the X-rays – the remnant of GK Persei (1901). The existence of such a nebulosity brings about the possibility of other nova remnants emitting X-rays. I calculate that the X-ray luminosity should be about 10²⁶–10³³ ergs s⁻¹ on the onset of cooling for nova remnants. I have done an archival search on 250 classical and recurrent nova candidates using Chandra, XMM-Newton, ROSAT and ASCA databases. There is no significant extended emission detected which places an upper limit of F_x < × 10⁻¹² erg s⁻¹ cm⁻² (unabsorbed). Only exceptions are GK Per, RR Pic and DQ Her (all observed by Chandra ACIS-S and GK Per also by ROSAT HRI) where the latter two show marginal extended emission in the X-rays associated with emission knots (DQ Her) or an equatorial ring (RR Pic).     

Effects of large scale magnetic fields in the dayside ionosphere of Venus

The ion density and magnetic field data from the Pioneer Venus Orbiter for the first three dayside periapsis passes have been analysed to study the effect of the large-scale fields upon the dayside ion density profiles. The peak value of the O⁺ density in a strongly magnetised ionosphere often shows an enhancement as compared to a close non-magnetic orbit. Further, the height of the O⁺ peak shows a positive correlation with the height of the minimum of the magnetic field profile. Contrary to earlier findings, the compressional effects of the magnetic fields are observed even at near-terminator locations.     

Two new hot white dwarfs in a region of exceptionally low hi density

We report the discovery of two hot white dwarfs which have the lowest line-of-sight neutral hydrogen column densities yet measured. The stars were found independently by the ROSAT EUV, Montreal-Cambridge-Tololo, and Edinburgh-Cape surveys. Follow-up observations made using the Voyager 2 ultraviolet spectrometer reveal strong continua shortward of the 912Å Lyman limit from which we deduce that the neutral hydrogen column densities are 1.3 × 10¹⁷ and 2.0 × 10¹⁷ atoms cm⁻².     

Hot hydrogen and deuterium in the exosphere of Venus

A theoretical study of the production, thermalization and escape, of hot atomic hydrogen and deuterium in the exosphere of Venus is presented. The approach adopted involves the quantum mechanical calculation of the charge exchange collision cross sections for (H⁺, H) and (D+, H) collisions, the production of translationally energetic atoms, and their ensuing thermalization and escape from Venus. A kinetic theory which employs the quantum mechanical collision cross sections and accounts for the production, thermalization and escape of hot atoms is described. Preliminary numerical results for escape fluxes calculated with density and temperature profiles as provided from the Pioneer Venus orbiter are presented.     

The ion energy spectra in the ring current during the geomagnetic storm of February, 1986

Using data from the CHEM instrument on the AMPTE/CCE spacecraft, we follow the development of the ring current energy spectra (1–300 keV/e) of the ion species H⁺, O⁺, He⁺, and He⁺⁺ in the post-noon and pre-noon local time sectors during the geomagnetic storm of February 1986. By comparing displays of phase space density, f, vs. magnetic moment, μ, we can distinguish between enhancements due to newly injected ions and those due to adiabatic energization of a pre-existing population. In both the local time sectors, the initial drop in Dst is associated with enhanced phase space densities of all species. The spectra observed during the pass when the Dst dropped to a minimem of −312 nT show a strong local time asymmetry. In the post-noon sector, the spectra showed the influx of a new population of ions, rich in O⁺ and He⁺⁺. In the pre-noon sector, the flux increase was consistent with adiabatic energization of the ion population injected earlier in the storm. This local time difference is consistent with a greatly enhanced convection electric field which brings a new population from the magnetotail to the post-noon, but not the pre-noon local time sector.     

A serendipitous survey for galaxy clusters by the XMM-Newton Survey Science Center

We describe the initial results of a programme to detect and identify extended X-ray sources found serendipitously in XMM-Newton observations. We have analyzed 186 EPIC-PN images at high galactic latitude with a limiting flux of 1 × 10⁻¹⁴ erg cm⁻² s⁻¹ and found 62 cluster candidates. Thanks to the enhanced sensitivity of the XMM-Newton telescopes, the new clusters found in this pilot study are on the average fainter, more compact, and more distant than those found in previous X-ray surveys. At our survey limit the surface density of clusters is about 5 deg⁻². We also present the first results of an optical follow-up programme aiming at the redshift measurement of a large sample of clusters. The results of this pilot study give a first glimpse on the potential of serendipitous cluster science with XMM-Newton based on real data. The largest, yet to be fulfilled promise is the identification of a large number of high-redshift clusters for cosmological studies up to z = 1 or 1.5.     

碘工质射频离子推力器栅极系统束流特性仿真

为分析碘工质射频离子推力器束流特性,应用粒子云网格算法（PIC）,对碘工质射频离子推力器栅极系统进行三维数值仿真。碘工质电离产物中除了大量存在的I⁺,还包含少量I₂⁺、I²⁺、I³⁺几种多价离子。对添加多价离子前后束流特性的仿真结果进行对比,得出该栅极系统离子空间分布、电势分布、离子相空间分布以及束流、束流发散角,并对变密度工况下束流大小进行统计。计算结果表明,程序能较好地模拟离子在栅极系统中的运动情况：添加多价离子后,等离子体悬浮电势有所上升,鞍点电势有所下降,但整体电势分布的变化幅度较小;添加多价离子后束流大小略有增加,束流发散角略有减小,通过理论分析可知仿真所得理论推力及理论比冲均有小幅度增加;放电室等离子体数密度增加到约2.4×10¹⁷m^-3时,该栅极系统达到了束流引出的极限,后续增大等离子体密度引出束流不增反降。模拟结果可以为碘工质射频离子推力器栅极系统的设计提供参考。     

不同热解温度下酚醛树脂复合材料渗透率测试

为了获得不同热解温度下酚醛树脂复合材料渗透率,设计搭建了复合材料气体渗透过程实验测量装置,提出了一种测量复合材料渗透率的方法,基于达西定律获得了复合材料渗透率。以不同热解温度下酚醛树脂复合材料为研究对象,进行了气体渗透过程实验测量,获得了材料上下表面气体压力变化曲线,同时得到了渗透过材料的气体流量,进而通过达西定律得出材料的渗透率。结果表明,该实验装置能够实现复杂孔隙复合材料的渗透率的测量。整体上,热解温度越高,渗透率越大。热解温度为400℃,渗透率量级在10-13;600℃和800℃时,渗透率量级在10-11。材料渗透率K和热解温度T满足K=9.7×10-14T-4×10-11。该实验结果为该类材料的渗透和热质扩散性能分析提供了基础物性数据。      

Do we know the cosmic-ray boosters?

The literature on cosmic-ray acceleration tends to favour strong shocks (in supernovae, stellar and galactic winds) over compact boosters. Difficulties are posed by the spectrum which does not reveal the implied upper cutoff (at E = 10^13±1 eV), by the energy-dependent anisotropy at the high-energy end (at E 10¹⁸ eV), the missing hydrogen, the large required boosting efficiency, the high positron abundance at E 10 GeV, detailed studies of supernova shells, and by an inadequacy of the Sedov-Taylor model for supernova explosions. Solar and solar-wind data support single-step or few-step accelerations because of the large observed anisotropies and short time scales.

The importance of spindown in compact binary systems is often underestimated. Several neutron-star binaries have been detected at cosmic γ-ray energies. Cosmic-ray escape from the Galaxy may proceed supersonically through narrow tubes rather than via convective diffusion.     

Investigation of magnetospheric processes with the use of a source of strong magnetic field in the ionosphere

More than 20 years ago V.P. Shabansky suggested that the magnetic system installed aboard the satellite, could be used as a physical instrument for studying the processes which occur in the near Earth space. The corresponding space scales of an artificial “magnetosphere”—“magnisphere”—are 10 m in the experiment with relatively small magnets in the ionosphere and 100 m in the solar wind. The corresponding similarity criteria are estimated. The possible scheme of the experiment with a superconducting magnet (magnetic moment 10⁵ A · m²) installed aboard the satellite is considered. The experimental complex includes a number of systems for measuring the fluxes of charged particles in a wide energy range, DC electric and magnetic fields, the electromagnetic fields in different frequency bands (from X-rays to radio). The scientific objectives are discussed in detail.     

Fluctuation analyses of the X-ray background

We review recent progress in the use of analyses of fluctuations in the cosmic X-ray background (XRB) to determine the source counts below the detection thresholds. Three flux domains are discussed: the range around 10⁻¹²erg cm⁻² s⁻¹ where the Ginga and Einstein Observatory results remain inconsistent unless the sources at these fluxes (mainly Seyfert galaxies) are highly absorbed at low energies, the 10⁻¹⁴erg cm⁻² s⁻¹ zone where the flattening of the source counts predicted by fluctuation analyses of Einstein Observatory images is now confirmed by Rosat, and the 10⁻¹⁵erg cm⁻² s⁻¹ flux domain, where fluctuation analyses of Rosat images show that source counts remain subeuclidean with very little contribution to the XRB coming from these sources.     

The 2.5 to 5 microns spectrum of comet Halley from the IKS instrument of Vega

Results of the 2.5–5 micron spectroscopic channel of the IKS instrument on Vega are reported and the data reduction process is described. H₂O and CO₂ molecules have been detected with production rates of 10³⁰ s⁻¹ and 1.5 10²⁸ s⁻¹ respectively. Emission features between 3.3 and 3.7 microns are tentatively attributed to CH - bearing compounds - CO is marginally detected with a mixing ratio CO/H₂O 0.2. OH emission and H₂O - ice absorption might also be present in the spectra.     

Rocket observation of the ultraviolet spectrum of comet Halley

An ultraviolet sounding rocket telescope/spectrograph experiment observed Comet Halley on 26 February 1986, 17 days after perihelion. From the long-slit spectra, the production rates of O, C, and CO are calculated. The derived water production rate is a lower limit of 5.0 × 10²⁹ s⁻¹ and the volume mixing ratio of CO to H₂O is 21%. The predicted brightness distribution from a radial outflow model with H₂O and CO as parent molecules are in accordance with the measured spatial profiles of OI and CO emissions. The ratio of the production rates of CO to C is 2.7 which is consistent with the carbon source being the photodissociation of CO. However, the radial outflow model which best fits the CO data predicts significantly weaker CI emissions than was observed. A better fit to the carbon data is found when an inner coma source of C at a rate of 3% of the water production rate is included in the model.     

Meteorites in Antarctica — Statistics on falls, concentration, recovery and alteration on ice-sheet

The Antarctic meteorites are distributed on the blue-ice area surfaces in the ablation zone of the Antarctic ice-sheet, to where meteorites have been transported by the ice-flow within the ice-sheet from the wider accumulation zone. Among the Antarctic meteorite collection H- and L-chondrites are most abundant; this is also true in the non-Antarctic meteorite collection. Meteorite showers also are involved in the collection. Several new types of stony meteorites have been discovered from the Antarctic meteorite collection. The mass and shape of Antarctic meteorites are in agreement with those of resultant fragments of high-speed impact basaltic rocks. In Antarctica, small fragments of meteorite smaller than 1 kg in weight can easily be found and collected. The solidification and the gas retention ages of Antarctic meteorites also are concentrated around 4.5×10⁹ years, but some of them are considerably younger. Their cosmic-ray exposure ages are extended up to 9×10⁶ years and their terrestrial ages are 9×10⁴-7×10⁵ years.