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.     

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.     

Energy content of accelerated electrons and ions in intense solar flares

The energy content of nonthermal particles in solar flares is shared between accelerated electrons and ions. It isimportant for understanding the particle acceleration mechanism in solar flares. Yohkoh observed a few intense flares which produced both strong gamma-ray lines and electron bremsstrahlung continuum. We analyze energy spectra of X-class solar flares on October 27, 1991(X6.1), November 6, 1997 (X9.4), July 14, 2000 (X5.7) and November 24, 2000 (X2.3). The accelerated electron and proton spectra are derived from a spectral analysis of their high-energy photon emission and the energy contents in >1 MeV electrons and >10 MeV protons are estimated to be 6×l0²⁸ – 4×10³⁰ and 2×10²⁸ – 5×10²⁹ erg, respectively. We study the flare to flare variation in the energy content of >1 MeV electrons and >10 MeV protons for the four Yohkoh gamma-ray flares. Ratios of >1 MeV electron energy content to >10 MeV proton energy content are roughly within an order of magnitude.     

CMB anisotropy testing from small satellites

We review the advantages and possibilities of small satellites. New results of data reduction of the satellite-borne experiment RELICT-1 are presented. For the inflation spectrum of primordial perturbations we obtained the estimate for quadrupole component 6·10⁻⁶ <ΔT₂/T<3.3·10⁻⁶. The RELICT-2 mission will provide a possibility of measurement of CBR anisotropy down to the level less than ΔT₂/T = 10⁻⁸. We present the results of engineering testing of RELICT-2 measurement system and discuss ways of improving of the radiometers sensitivities.     

High spectral resolution Fabry-Perot interferometer measurements of comet Halley at H-alpha and 6300 Å

A 40.6 cm Newtonian telescope has been interfaced to the Fabry-Perot interferometer at the Arecibo Observatory to make high spectral resolution measurements of Comet Halley emissions at 6562.72 Å (H-alpha) and 6300.3 Å (OI). In March 1986 the H-alpha surface brightness for a 5′.9 field of view centered on the comet nucleus decreased from 39±7.8 rayleighs on 12 March to 16±3.8 rayleighs on 23 March. The atomic hydrogen production rate on 12 March 1986 was 1.62±0.5 × 10³⁰ s⁻¹, and on 23 March 1986 it was 6.76±2.3 × 10²⁹ s⁻¹. Using spectral resolution of 0.196 Å, we found the atomic hydrogen outflow velocity to be approximately 7.9±1.0 km s⁻¹. In general, the H-alpha spectra are highly structured, and indicative of a multiple component atomic hydrogen velocity distribution. An isotropic outflow of atomic hydrogen at various velocities is not adequate to explain the spectra measured at H-alpha. The 6300.3 Å emission of O(1D) had a surface brightness of 81±16 rayleighs on 15 March 1986, and 95±11 rayleighs on 17 March 1986. After adjustment for atmospheric extinction, the implied O(1D) production rate on 15 March is 6.44±3.0 × 10²⁸ s⁻¹, and the production rate on 17 March is 5.66±2.7 × 10²⁸ s⁻¹. These spectra included a feature at 6300.8 Å that we attribute to NH₂. The brightness of this emission feature was 37±11 rayleighs on 15 March.     

Interaction of growth-determining systems with gravity

The experiments have been carried out with lettuce shoots on board the Salyut-7 orbital station, the Kosmos-1667 biological satellite and under ground conditions at 180° plant inversion. By means of the centrifuge Biogravistat-1M the threshold value of gravitational sensitivity of lettuce shoots has been determined on board the Salyut-7 station. It was found to be equal to 2.9 × 10⁻³g for hypocotyls and 1.5 × 10⁻⁴g for roots. The following results have been received in the experiment performed on board the Kosmos-1667 satellite: a) under microgravity the proliferation of the meristem cells and the growth of roots did not differ from the control; b) the growth of hypocotyls in length was significantly enhanced in microgravity; c) under microgravity transverse growth of hypocotyls (increase in cross sectional area) was significantly increased due to enhancement of cortical parenchyma cell growth. At 180° inversion in Earth's gravity root extension growth and rate of cell division in the root apical meristem were decreased. The determination of DNA-fuchsin value in the nuclei of the cell root apexes showed that inversion affected processess of the cell cycle preceeding cytokinesis.     

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.     

Microwave imaging observation of an electron stream in a solar flare

We report a Nobeyama Radioheliograph (NoRH) microwave observation of a propagating feature of non thermal emission in a solar flare. The flare had a very extended source well resolved by NoRH. In the rising phase of the microwave burst, a non-thermal gyrosynchrotron source was observed by the high-rate (10 images per second) observations to propagate from one end of the loop to the other with a speed of 9 × 10⁴ km s⁻¹. We interpret this non-thermal propagating source is emitted from streaming electrons.     

Near infrared observations of comet Halley from Vega 2

Spatial distribution of the continuum radiation in the range of 0.95–1.9 μm presumes total dust production rate of the comet of 10ρ tonne s⁻¹ (ρ is the dust material density) and its angular distribution proportional cos . Observations of the water vapor band at 1.38 μ m reveal strong jets, their time shift from the dust jet measured in situ is consistent with gas velocity of 0.82±0.1 km s⁻¹ and dust velocity of 0.55±0.08 km s⁻¹. The OH vibrational-rotational bands observed are excided directly via photolysis of water vapor. Water vapor production rate deduced from the H₂O band and OH band intensities is 8×10²⁹ s⁻¹. Intensity of the CN(0,0) band result in the CN column density of 9×10¹² cm⁻², i.e. larger by a factor of 3 than given by the violet band.     

First results of plasma and neutral gas measurements from Vega-1/2 near comet Halley

Based on the ion, electron and neutral gas observations, performed by five of the six sensors comprising the PLASMAG-1 experiment on board VEGA-1 and -2, the following results are discussed: (1) the existence of the bow shock and its location at 1.1×10⁶ km for VEGA-1 inbound; (2) the existence of a cometopause and its location at 1.6×10⁵ km for VEGA-2 inbound; (3) the plasma dynamical processes occurring inside the cometosheath; (4) the phenomena taking place within the cometary plasma region including mass-spectroscopy of cometary ions at distances 1.5×10⁴ km; (5) the existence of keV electrons near closest approach to the nucleus; and (6) the radial dependence of the cometary neutral gas and the comparison with model calculations, yielding a mean ionization scale length of 2×10⁶ km and an overall production rate of 1.3×10³⁰ molecules s⁻¹ for VEGA-1 inbound. The results are also discussed in the context of the other, both remote and in-situ, observations, performed on board the VEGA- and GIOTTO-spacecraft.     

Hard X-ray focusing optics up to 80 keV for the future missions

X-ray telescopes have been providing high sensitivity X-ray observations in numerous missions. For X-ray telescopes in the future, one of the key technologies is to expand the energy band beyond 10 keV. We designed depth-graded multilayer, so-called supermirrors, for a hard X-ray telescope in the energy band up to 40 keV using lightweight thin-foil optics. They were successfully flown in a balloon flight and obtained a hard X-ray image of Cyg X-1 in the 20–40 keV band. Now supermirrors are promising to realize a hard X-ray telescope. We have estimated the performance of a hard X-ray telescope using a platinum–carbon supermirror for future satellite missions, such as NeXT (Japan) and XEUS (Europe). According to calculations, they will have a significant effective area up to 80 keV, and their effective areas will be more than 280 cm² even at 60 keV. Limiting sensitivity will be down to 1.7 × 10⁻¹³ erg cm⁻² s⁻¹ in the 10–80 keV band at a 100 ks observation. In this paper, we present the results of the balloon experiment with the first supermirror flown and projected effective areas of hard X-ray telescopes and action items for future missions.     

Extreme starburst or central activity in X-ray luminous IRAS galaxies

ROSAT All Sky Survey observations of IRAS galaxies have revealed up to now a number of 10 optically non-Seyfert galaxies with X-ray (0.1–2.4) luminosities up to a few 10⁴³erg · s⁻¹ (Boller et al. 1992). The sources are brighter than previous detection limits of a few 10⁴¹erg · s⁻¹ as found by Stocke et al. (1991) or Green, Anderson and Ward (1992) for Einstein sources. The optical classification is based on follow-up observations which indicate clearly the non-Seyfert (LINER and HII region-like galaxies) nature. Our investigations reveal that galaxies classified as non-Seyferts on the basis of optical spectroscopy may reach exceptionally high X-ray luminosities which are similar to that of Seyfert galaxies. On the basis of the present observational material we suppose a hidden low luminosity AGN in the centre of these objects as the source of energy production. The objects are of interest when evaluating starburst versus central activity.     

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.     

Her X-1 as seen in the ROSAT all-sky survey

ROSAT performed the first, spectrally resolved, soft X-ray observations of Her X-1 in the SHORT-ON state of the 35^d cycle. The data were taken during the All-Sky survey covering the range 0.1–2.4 keV. The mean luminosity in the ROSAT bandpass is 1.5 × 10³⁶ ergs sec⁻¹. Timing analysis of the data revealed a highly significant signal at a period of 1.237749(1) sec. Finally, we present evidence to support the hypothesis that the resuction in intensity during the SHORT-ON state is caused by hot matter absorption in the disk.     

Earth encounter velocities for interplanetary meteoroids

The speed distribution of meteoroids encountering the Earth is shown to be similar for all meteoroid masses in the range 1 g to 10⁻¹² g. The speed distribution of interplanetary meteoroids encountering the Earth has usually been inferred from meteor observations. This paper reviews commonly quoted distributions and introduces more recent estimates. The influence quoted measurement uncertainties have on the distribution of Earth encounter velocities presented by Sekanina and Southworth (1975) and Erickson (1968) is presented. The Divine (1993) model of interplanetary meteoroids fits a set of orbital distributions to a wide range of spacecraft and ground based dust detector observations. By ‘flying’ the Earth through this model the distribution of geocentric encounter velocities has been obtained for typical particle masses, 10⁻⁹ and 10⁻¹² g while those at 10⁻⁴ and 10⁻⁵ g are shown to be in error.     

Study of the luminosity-dependent cyclotron resonance energies of the binary X-ray pulsar 4U 0115+63 with RXTE

We report on the luminosity dependent change of the cyclotron resonance energy obtained from a transient X-ray pulsar, 4U 0115+63. Using RXTE data observed on 1999 March, we found that the fundamental resonance energy stayed constant (11 keV) when the source luminosity was above 5 × 10³⁷ erg s⁻¹. As the luminosity decreased below 5 × 10³⁷ erg s⁻¹, the fundamental resonance energy gradually increased up to 16 keV at 0.16 × 10³⁷ erg s⁻¹. The luminosity dependence of the resonance energy can be understood by the change of the accretion column height.     

Experimental drop tube of the metallurgy department of Grenoble

The drop tube which will be available in the “Centre d'Etudes Nucléaires de Grenoble” is described. Its main features are the following: - Dimensions : Drop height : 47.1 m Drop time : 3.1 s Tube inside diameter : 0.2 m - Experimental atmosphere : 1 Ultra-vacuum : 10⁻⁶ to 10⁻⁷ Pa - Residual gravity level : 10⁻⁸ to 10⁻⁹ g according to the vacuum level and drop diameter.

This facility is unique insofar as it enables experiments to be performed under ultra-vacuum conditions which, by delaying the formation of surface oxides, should contribute to improving maximum undercooling values.

The techniques used for obtaining small metallic drops (0.5 to 3 mm) are described. The availability of this instrument for the scientific community is also foreseen by the french sponsoring organizations (CEA, CNES, CNRS) ; some practicle informations will be given to potential experimenters.     

Correlations between neutral and ionized solar wind

We report results of a statistical study correlating ionized solar wind (ISW) fluxes observed by ACE during late 2000 and throughout 2001 with neutral solar wind (NSW) fluxes observed by IMAGE/LENA over the same period. The average correlation coefficient between the neutral and ionized solar wind is 0.66 with correlations greater than 0.80 occurring about 29% of the time. Correlations appear to be driven by high solar wind flux variability, similar to results obtained by in situ multi-spacecraft correlation studies. In this study, however, IMAGE remains inside the magnetosphere on over 95% of its orbits. As a function of day of year, or equivalently ecliptic longitude, the slope of the relationship between the neutral solar wind flux and the ionized solar wind flux shows an enhancement near the upstream direction, but the symmetry point appears shifted toward higher ecliptic longitudes than the interstellar neutral (ISN) flow direction by about 20°. The estimated peak interstellar neutral upstream density inside of 1 AU is about 7 × 10⁻³ cm⁻³.     

From solar nanoflares to stellar giant flares: Scaling laws and non-implications for coronal heating

In this study we explore physical scaling laws applied to solar nanoflares, microflares, and large flares, as well as to stellar giant flares. Solar flare phenomena exhibit a fractal volume scaling, V(L)  L^1.9, with L being the flare loop length scale, which explains the observed correlation between the total emission measure EM_p and flare peak temperature T_p in both solar and stellar flares. However, the detected stellar flares have higher emission measures EM_p than solar flares at the same flare peak temperature T_p, which can be explained by a higher electron density that is caused by shorter heating scale height ratios s_H/L ≈ 0.04–0.1. Using these scaling laws we calculate the total radiated flare energies E_X and thermal flare energies E_T and find that the total counts C are a good proxy for both parameters. Comparing the energies of solar and stellar flares we find that even the smallest observed stellar flares exceed the largest solar flares, and thus their observed frequency distributions are hypothetically affected by an upper cutoff caused by the maximum active region size limit. The powerlaw slopes fitted near the upper cutoff can then not reliably be extrapolated to the microflare regime to evaluate their contribution to coronal heating.     

Distinctive spatial configuration of a class ofmicrowave flaring sources

We discuss a class of microwave flares whose source regions exhibit a distinctive spatial configuration; the primaryenergy release in these flares results from the interaction between emerging magnetic flux and an existing overlying region. Such events typically exhibit radio, X-ray and EUV emission at the main flare site (the site of interaction) and in addition radio emission at a remote site up to 1 × 10⁵ km away in another active region. We have identified and studied more than a dozen microwave flares in this class, in order to arrive at some general conclusions on reconnection and energy release in such solar flares. Typically, these flares show a gradual rise showing many subsidiary peaks in both radio and hard X-ray light curves with a quasi-oscillatory nature with periods of 5–6 seconds, a bright compact X-ray & EUV emitting loop in the main flare source, a delay of the radio emission from the remote source relative to the main X-ray-emitting source. The magnetic field in the main flare site changes sharply at the time of the flare, and the remote site appears to be magnetically connected to the main flare site.