A simple two-layer model for the Uranus satellites

A two-layer model of a satellite interior with a rocky core with a density 3–3.4 g cm^-3 and with a H₂O mantle with a density 0.94–1.2 g cm^-3 is applied for the icy satellites. The case of Mimas is discussed separately. A comparison of the results with these obtained for more complicated models as applied for Jupiter and Saturn icy satellites has been carried out. This comparison shows that the two-layer model offers a reasonable approximation and, therefore, it can be applied for the satellites of Uranus. We obtained the dimensionless core radii 0.55–0.74, 0.45–0.68, 0.59–0.67, 0.55–0.65, and dimensionless core masses 0.42–0.72, 0.26–0.63, 0.47–0.61, 0.41–0.57, for Ariel, Umbriel, Titania, and Oberon, respectively.Institute of Geophysics of Warsaw University, Warszawa, Poland.     

X-ray observation of the Jovian impacts of comet Shoemaker - Levy 9

An ASCA observation of the Jovian impact of the comet Shoemaker-Levy 9 is reported. Four impacts of H, L, Q1 and R were observed and four impacts of B, C, G, and Q2 were observed within 60 minutes after their impacts. No significant flaring of X-ray emission was observed. Upper limit X-ray fluxes of 90 % confidence level, averaged 5 minutes just after the impacts, were 2.4 × 10^–13 erg sec^–1 cm^–2, 3.5 × 10^–13 erg sec^–1 cm^–2, 1.6 × 10^–13 erg sec^–1 cm^–2 and 2.9 × 10^–13 erg sec^–1 cm^–2 for the impacts of H, L, Q1 and R, respectively, in the 0.5(0.7 for H and Q1)–10 keV energy range. However, a hint of X-ray enhancement around Jupiter from July 17 to July 19 was detected with about 2 6 × 10^–14 erg sec^–1 cm^–2 in the 0.5–10 keV energy range.     

Interpretation of the solar continuum from 1680 to 600 Å. Model of the transition region photosphere-chromosphere and of the chromosphere

An interpretation is given of the observations of the continuous solar radiation in the spectral range 600–1700 Å. The model allows for deviations from LTE of H, C, Si and S, and is in hydrostatic equilibrium. The predicted intensity from 1680 to 1520 Å has virtually no dependence on the electron temperature variation in the optical depth range 10^–3–4 × 10^–5, at 5000 Å; the brightness temperature is compatible with a low electronic temperature minimum near the optical depth 10^–4. The model of the low chromosphere is characterized by a steep temperature gradient. The model satisfies observations at millimeter wavelengths.     

The Wide Band Spectrometer on the SOLAR-A

The SOLAR-A spacecraft has spectroscopic capabilities in a wide energy band from soft X-rays to gamma-rays. The Wide Band Spectrometer (WBS), consisting of three kinds of spectrometers, soft X-ray spectrometer (SXS), hard X-ray spectrometer (HXS) and gamma-ray spectrometer (GRS), is installed on SOLAR-A to investigate plasma heating, high-energy particle acceleration, and interaction processes. SXS has two proportional counters and each counter provides 128-channel pulse height data in the 2–30 keV range every 2 s and 2-channel pulse count data every 0.25 s. HXS has a NaI scintillation detector and provides 32-channel pulse height data in the 20–400 keV range every 1 s and 2-channel pulse count data every 0.125 s. GRS has two identical BGO scintillation detectors and each detector provides 128-channel pulse height data in the 0.2–10 MeV range every 4 s and 4-channel pulse count data (0.2–0.7, 0.7–4, 4–7, and 7–10 MeV) every 0.25–0.5 s. In addition, each of the BGO scintillation detectors provides 16-channel pulse height data in the 8–100 MeV range every 4 s and 2-channel pulse count data (8–30 and 30–100 MeV) every 0.5 s. The SXS observations enable one to study the thermal evolution of flare plasma by obtaining time series of electron temperatures and emission measures of hot plasma; the HXS observations enable one to study the electron acceleration and heating mechanisms by obtaining time series of the electron spectrum; and the GRS observations enable one to study the high-energy electron and ion acceleration and interaction processes by obtaining time series of electron and ion spectra.After the launch the name of SOLAR-A has been changed to YOHKOH.     

On the reliability of the so-far performed tests for measuring the Lense–Thirring effect with the LAGEOS satellites

In this paper, we critically discuss the so-far performed attempts aimed at the detection of the general relativistic gravitomagnetic Lense–Thirring effect in the gravitational field of the Earth with the existing LAGEOS satellites. In the latest reported measurement of the gravitomagnetic shift with the nodes of the LAGEOS satellites and the second generation GRACE-only EIGEN-GRACE02S Earth gravity model over an observational time span of 11 years a 5–10% total accuracy is claimed at 1–3σ, respectively. We will show that, instead, it might be 15–45% (1–3σ) if the impact of the secular variations of the even zonal harmonics is considered. Possible strategies in order both to make more robust and reliable the tests with the node-only LAGEOS–LAGEOS II combination used and to overcome the problems affecting it with other alternative combinations are presented.     

On the fourier spectrum analysis of the solar neutrino capture rate

Periodic variations in Davis' experimental data concerning the solar neutrino capture rate are derived on the basis of a Fourier spectrum analysis. Variations in the ³⁷Ar production rate are obtained for a series of randomly spaced observations in the period 1970–1985 (runs 18–89). The harmonic analysis of runs 18–89 has determined solar neutrino capture rate variations with periods of 8.33, 5.00, 2.13, 1.61, 0.83, 0.61, 0.54, and 0.51 yr, thereby confirming earlier calculations performed for the set of runs 18–69 (1983), 18–74 (1985a), and 18–80 (1985b). The results also confirm those of Sakurai (1979) who showed that there is strong evidence that the observed solar neutrino flux has a tendency to vary with quasi-biennial periodicity. We show that the results of the Fourier spectrum analysis do not depend upon certain high or low values in Davis' experimental data.     

Statistical Weights and Selective Height Corrections in the Determination of the Solar Rotation Velocity

Observations of the Sun performed at 37 GHz with the 14-m radio telescope of the Metsähovi Radio Observatory were analyzed. Rotation velocities were determined, tracing Low Temperature Regions (LTRs) in the years 1979–1980, 1981–1982, 1987–1988, and 1989–1991. Statistical weights were ascribed to the determined rotation velocities of LTRs, according to the number of tracing days. Measured changes of the rotation velocity during the solar activity cycle, as well as a north–south rotation asymmetry, are discussed. The results obtained with and without the statistical weights procedure are compared, and it was found that the statistical significance of the solar differential rotation parameters' changes is higher when the statistical weights procedure is applied. A selective application of the height correction on LTR's positions has not removed the cycle-related changes nor the north–south asymmetry of the solar rotation measured tracing LTRs. So, projection effects cannot explain these changes. The differential rotation of LTRs is more rigid than the differential rotation obtained tracing magnetic features and measuring Doppler shifts, which can be explained by the association rate of the LTRs' positions with rigidly rotating `pivot points'. The observed cycle-related changes and the north–south asymmetry of the rotation velocity of LTRs are consistent with the cycle-related changes and the north–south asymmetry of the association rate between LTRs and pivot points.     

The hypothesis of the Fornax system at perigalacticon. Are the stars and the universe older?

Published in Astrofizika, Vol. 37, No. 2, pp. 307–312, April–June, 1994.     

Nature of the variability of the subfour V 1143 Ori

Byurakan Astrophysical Observatory; Tonantzintla Observatory, Mexico. Translated from Astrofizika, Vol. 34, No. 2, pp. 175–180, March–April, 1991.     

On the energy distribution in the continuous spectrum

Byurakan Astrophysical Observatory; TETRA Corporation, USA. Translated from Astrofizika, Vol. 33, No. 1, pp. 39–45, July–August, 1990.     

The emission of solar X-rays in the 0.5–3 Å wavelength range and its relation to the magnetic configuration of active centers

The slowly varying component of solar X-rays in the 0.5–3 Å wavelength range has been studied using data obtained by the satellite Explorer 30 (Solrad 8). The intensity of these X-rays is poorly correlated with the centimeter radio flux, contrary to the good correlation found in the spectral bands 1–8, 8–16 and 44–60 Å. On the other hand the 0.5–3 Å X-ray intensity is often connected to the development of a specific magnetic configuration in the sun spot group which may thus be associated with the X-ray producing active center.     

Cosmological solutions of the Friedmann type in the tensor-scalar theory of gravitation

Erevan State University. Translated from Astrofizika, Vol. 36, No. 4, pp. 583–592, October–December, 1993.     

Temperature changes on the Tibetan Plateau during the past 600 years inferred from ice cores and tree rings

The climatological signal of δ¹⁸O variations preserved in ice cores recovered from Puruogangri ice field in the central Tibetan Plateau (TP) was calibrated with regional meteorological data for the past 50 years. For the period AD 1860–2000, 5-yearly averaged ice core δ¹⁸O and a summer temperature reconstruction derived from pollen data from the same ice core were compared. The statistical results provide compelling evidence that Puruogangri ice core δ¹⁸O variations represent summer temperature changes for the central TP, and hence regional temperature history during the past 600 years was revealed. A comparison of Puruogangri ice core δ¹⁸О with several other temperature reconstructions shows that broad-scale climate anomalies since the Little Ice Age occurred synchronously across the eastern and southern TP, and the Himalayas. Common cold periods were identified in the 15th century, 1625–1645 AD, 1660–1700 AD, 1725–1775 AD, 1795–1830 AD, 1850–1870 AD, 1890–1920 AD, 1940–1950 AD, and 1975–1985 AD. The period 1725–1775 AD was one of the most prolonged cool periods during the past 400 years and corresponded to maximum Little Ice Age glacier advance of monsoonal temperate glaciers of the TP.     

Solar energetic particle events at the rise phase of the 23rd solar activity cycle registered aboard the spacecraft &;#x201C;INTERBALL-2&;#x201D;

The experiment with 10K-80 aboard the INTER-BALL-2 (which detects protons with energies > 7, 27–41, 41–58, 58–88, 88–180 and 180–300 MeV) registered six events of the solar energetic particle (SEP) increase. These events are during the initial rise phase of the 23rd solar activity cycle. Solar flares with the SEP generation are accompanied by coronal mass ejection (CME). Here we analyze the dynamics of the differential energy spectrum at different phases of the SEP increase.     

Power spectra of the interplanetary magnetic field

Power spectra based on Pioneer 6 interplanetary magnetic field data in early 1966 exhibit a frequency dependence of f ^–2 in the range 2.8 × 10^–4 to 1.6 × 10^–2 cps for periods of both quiet and disturbed field conditions. Both the shape and power levels of these spectra are found to be due to the presence of directional discontinuities in the microstructure (< 0.01 AU) of the interplanetary magnetic field. Power spectra at lower frequencies, in the range of 2.3 × 10^–6 to 1.4 × 10^–4 cps, reflect the field macrostructure (> 0.1 AU) and exhibit a frequency dependence roughly between f ^–1 and f ^–3/2. The results are related to theories of galactic cosmic-ray modulation and are found to be consistent with recent observations of the modulation.     

Observing the CMB at high-ℓ using the VSA and AMI

We discuss two experiments – the Very Small Array (VSA) and the Arcminute MicroKelvin Imager (AMI) – and their prospects for observing the CMB at high angular multipoles. Whilst the VSA is primarily designed to observe primary anisotropies in the CMB, AMI is designed to image secondary anisotropies via the Sunyaev–Zel’dovich effect. The combined ℓ-range of these two instruments is between ℓ=150 and 10,000.     

Some remarks on the universal X-ray background

It is shown that a universal steady X-ray background with the energy flux 10^–7 erg cm^–2 s^–1 sr^–1 can arise as a superposition of radiation from pulsars (neutron stars) in various galaxies when it is taken into account that supernova outburst occurs in a galaxy at the rate of 10^–2/year.     

On the observed carbon underabundance in the atmospheres of B stars

Crimean Astrophysical Observatory. Translated from Astrofizika, Vol. 30, No. 1, pp. 99–110, January–February, 1989.     

On the reality of the observed chemical anomalies of Am stars in the light of their binary nature

Crimean Astrophysical Observatory. Translated from Astrofizika, Vol. 31, No. 3, pp. 519–525, November–December, 1989.     

A Study on the Long-term Spectral Variability of the Black-hole Candidate X-ray Binary Cyg X-1

Using the All-Sky Monitor (ASM, 1.5–12–kev) data of Rossi X-ray Timing Explorer (RXTE) from January 1996 to May 2005, we have made a detailed analysis of the correlation between photon-count rate and spectral hardness ratio HR2 (5–12 keV/3–5 keV) of the black-hole candidate X-ray binary Cyg X-1 in 3 energy bands, namely the A-band (1.5–3 keV), B-band (3–5 keV) and Cband (5–12 keV). By the study on the ASM data of 1-day time scale, we find: (1) When Cyg X-1 is in the soft state, the A-band photon-count rate and hardness ratio HR2 exhibit an anticorrelation, but in B-band and C-band there appears the positive correlation. When Cyg X-1 is in hard state, the photon-count rates in the A,B,C bands are all inversely correlated with the hardness ratio HR2; (2) No matter whether Cyg X-1 is in the soft state or the hard state, the hardness ratios HR2 and HR1 are always positively correlated. In addition, we have analyzed the “dwell by dwell” data of the ASM, and obtained the following interesting results: (1) In the period of MJD = 52600–52760 (while Cyg X-1 is in the hard state), the photon-count rates in the A-band and B-band are inversely correlated with HR2, but in the C-band there appears a relatively strong positive correlation; (2) During the hard state, a clear anticorrelation exists between the hardness ratios HR2 and HR1.