Recent work by Dyer and Morfill has shown that satellite measurements of the diffuse cosmic X-ray spectrum made with crystal scintillators may include errors due to radioactive spallation products formed in the detector by inner belt and cosmic ray protons.
An estimate is made of the magnitude of this source of background for the various experimental situations and it is shown that apparent features at 40 keV and 1 MeV are likely to be due to radioactive decays in the instruments. A review is made of experiments covering the range 1 keV-100 MeV in order to ascertain whether a single exponent spectrum is capable of fitting the experimental results. The astrophysical implications of such a spectrum are briefly considered.
Suggestions are made for the location and correction for background of future experiments.
相似文献By the analysis of the profiles of 20 weak lines observed at five centre-to-limb positions on the solar disk, radial and tangential components of the velocity amplitude of the photospheric motion field are derived in the range of optical depth - 3.0 ? lgτ5 ? +0.5.
相似文献Maps of the brightness distribution of the ‘quiet Sun’ at 80 and 160 MHz reveal the presence of features both brighter and darker than average. The ‘dark’ regions are well correlated with dark regions on UV maps; we deduce that they result from ‘coronal holes’. The ‘bright’ regions are associated with quiescent filaments and not plages or bright regions on microwave or UV maps; we deduce that they result from ‘coronal helmets’.
When coronal holes appear near the centre of the disk we can estimate the density and kinetic temperature in the holes from the radio observations. For a hole observed on 1972 July 20–21, we find T ≈ 0.8 × 106 inside the hole and T ≈ 1.0 × 106 in average regions outside the hole. Inside the hole the density is estimated to be about one-quarter of that in Newkirk's model of the spherically symmetric corona.
Variations in brightness at a fixed height above the limb are generally well correlated with scans at a similar height made with a K-coronameter. Occasional differences may result from streamers protruding beyond the limb from the back of the Sun. These can be seen by the K-coronameter but, because of refraction of the radio rays, not by the radio-heliograph.
相似文献We study the longitudinal magnetic field in a number of active limb prominences showing fields in excess of 30 G. The objects fall into three groups: surges, caps and active region prominences. There appears to be an upper limit of 150–200 G for the field strength in prominences.
A model of surges is presented in which a pre-surge axi-symmetric magnetic field is established by a line current in the corona. We observe particle acceleration in surges that indicates v×B≠0 in these objects during periods comparable to the Alfvén transit time.
The strong fields observed in caps seem to run between parts of active regions in accordance with Hale's law of sunspot group polarities.
相似文献Time-averaging technique is performed on a set of white light pictures obtained at μ=0.87. After eliminating short-lived granulations, the time-averaged pictures show some large scale but longlived brightness patterns which are not recognizable in any of the single frame snapshots. The patterns are brighter than the background and are co-spatial with the upper photospheric emissions and magnetic fields. We define these patterns as the white light network.
相似文献A brief review on the history of constructing Earth-like models of the Venusian interior is presented. Available observational data are analyzed. An explanation for the anomalously large ratio of the quadrupole gravitational moment J2 to the small parameter of Venus q is proposed. Thus, estimates were obtained for the precession constant and principal moments of inertia for the Earth-like model of Venus.
相似文献A mechanism is proposed explaining the structures consisting of plasma arcs, as observed in X-ray photographs of solar active regions. It is suggested that the width of the arcs corresponds to the cut-off wavelength of a Rayleigh-Taylor instability which develops due to a difference in density between the plasma in the arcs and the plasma in the surrounding region. The transverse component of the magnetic field necessary to stabilize the instability at a wavelength corresponding to the width of the arcs is estimated to be of the order of 0.1 G.
相似文献Attitude motion of spinning axisymmetric satellites in presence of gravity-gradient and solar radiation pressure torques is studied analytically. The approximate closed-form solution developed for the nonlinear, nonautonomous, coupled fourth-order system proves to be an excellent tool in locating periodic solutions of the system in both circular and noncircular orbits. The variational stability of the periodic motion is examined using the Floquet theory. The resonance analysis suggests the existence of critical combinations of system parameters leading to large amplitude oscillations.
相似文献This study constitutes the second phase of an effort devoted to the relative motion of two spheroidal rigid bodies.
An isolated binary system was considered whose components are bodies: (1) of comparable size; (2) of constant density; and (3) having the shape of an oblate ellipsoid of revolution with small meridional eccentricity.
The equations that determine the relative motion of the centroids and the angular motion for the two sets of body axes constitute a simultaneous system of seven nonlinear, second-order differential equations, for which solutions were obtained as power series in the two meridional eccentricities.
A recurrent procedure was formulated to ascertain the various approximations in terms of lower order terms; it gave rise to linear differential equations with constant coefficients for the angular variables and to differential equations of the Hill type for the other coordinates. The zero-order approximation for the motion of the centroids was assumed to be a Kepler elliptic orbit of small eccentricity.
The following contributions were made:
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(1)
The general solution to the zero-order approximation of the rotational motion was obtained in terms of elementary functions;
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(2)
Certain functionals, related to the Kepler motion and depending on two parameters, were expressed in terms of the mean anomaly up to the sixth power of the orbital eccentricity in order to evaluate the lower order terms of the various approximations;
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(3)
The secular terms were eliminated from the first-order approximation;
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(4)
The second-order approximation was also obtained; and
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(5)
An alternate procedure was suggested that might be more appropriate for achieving higher order approximations.
Methods for the determination of the average optical depth of formation of weak Fraunhofer lines are compared, and their relative merits are discussed. Distinction should be made between the region of origin of the emergent radiation, and of the line depression. For weak or fairly weak lines the average optical depth of formation of the line depression is the relevant quantity; it should be determined by using a computational scheme based on the classical weighting functions of line formation; other methods give physically unsignificant or conflicting results.
相似文献A stationary two-dimensional isothermal flow parallel to the magnetic lines of force is studied in connection with the hydrodynamic support of a spicule. Observed large extension into the corona (～ 6000 km) and high velocities (～ 25 km s-1) can be explained consistently if the effective kinetic temperature within a spicule could be about 104 K in the chromospheric region (z < 2000 km) and increase to about 2.5 × 104 K or more in the coronal region (z > 2000 km). In a special simple case, an analytic solution of equations of motion is obtained and is used for explaining why the pressure in a spicule can be higher than the normal surrounding pressure in upper levels.
Comparison between the effective kinetic temperatures for the spicule support and the empirical electron temperatures shows that they are about the same in lower levels (z < 2000 km) but contributions to the effective kinetic temperature other than the electron temperatures are necessary in higher levels (z > 2000 km). Thus, we postulate the role of acoustic waves that are enhanced by the presence of the magnetic field and are practically undamped in the accelerated flow in a spicule. The coupling between the acoustic waves and the outward expanding motion initiated at the foot of a spicule by the magnetic buoyancy and the solar oscillation is thought to be similar to the mechanism of a geyser in which the bubble formation in an ascending flow is fundamental. The magnetic field strength adequate to provide an appropriate circumstance for the occurrence of a spicule is considered to be about 200 G at the base of the chromosphere. Observational implications are briefly discussed.
相似文献We describe time-series observations of small-scale Ca ii emission features located outside the network in the quiet chromosphere. Simultaneous spectra in K and λ 8542 show unambiguously that the evolutionary behaviour of the K-line profile due to an outwardly propagating velocity pulse. Assuming that this pulse is a progressive acoustic wave, as suggested by the inferred flow parameters, we show that the wave loses mechanical energy in traversing the chromosphere. This implies that the bright Ca ii features (K-grains) are the manifestation of local heating in the chromosphere, possibly by shock waves.
相似文献The integration by recurrent power series of certain differential equations occurring in celestial mechanics is shown to be very much more efficient and accurate than that produced by classical one step methods. It is shown that for any such system of differential equations the machine time taken to carry out an integration is a minimum for a certain choice of the number of terms taken in the recurrent power series. In the two-body orbits considered this number is about 15. For the same accuracy criterion the power series is faster than the Runge-Kutta method of the fourth order by a factor which varies between 6 and 15 depending on the eccentricity of the orbit.
相似文献The Chelyabinsk meteorite sample of type LL5 was subjected to calcination in the specially constructed instrument in the temperature range 200–800°C in increments of 100°C. The composition of the obtained volatile constituents was examined on a chromatograph. Detected were: CO2, H2O, and N2 in concentrations of 5–40 μg/g of the sample; H2, CO, CH4, and H2S in concentrations of 0.1–2.0 μg/g. By observing changes in the selected component concentrations over time (up to 90 minutes), it was concluded that chemical reactions in the system between volatile components occur directly during outgassing.
相似文献Observations of the solar photosphere show spatially compact large-amplitude Doppler velocity events with short lifetimes. In data from the Imaging Magnetograph eXperiment (IMaX) on the first flight of the Sunrise balloon in 2009, events with velocities in excess of 4\(\sigma \) from the mean can be identified in both intergranular downflow lanes and granular upflows. We show that the statistics of such events are consistent with the random superposition of strong convective flows and p-mode coherence patches. Such coincident superposition complicates the identification of acoustic wave sources in the solar photosphere, and may be important in the interpretation of spectral line profiles formed in solar photosphere.
相似文献Long records of the wavelength oscillations of the solar 7699 Å potassium line have been obtained with an atomic-beam resonance-scattering apparatus taken to Kitt Peak. Data are presented giving the dependence of rms oscillation amplitude on the size of the area observed and power spectra of the oscillations are shown. The results are compared with recent work by others.
相似文献The resonance amongst three of the Galilean satellites is described in a way intended to demonstrate the similarities it has to the normal two-satellite resonance. The hypothesis that the resonance was formed by the action of tidal forces is discussed. The problem is too complicated to reach any firm conclusions, but the tidal hypothesis does not seem to be a satisfactory explanation.
相似文献Previously we have reported the detection of a sequence of three particle arrival events at energies above 1019 eV during one day and from a small sky region by two extensive air shower (EAS) arrays. We have shown that the probability of a chance coincidence of the three events is very low and suggested the arrival of a short-lived particle beam at the Earth. Here we refine the energies of the recorded particles and discuss a possible beam formation mechanism that explains the observational results.
相似文献The investigation of the models of the contemporary Sun with a mixed core has shown that the amplitude of some gravity modes of oscillations of the star can be mainly concentrated in the central region. This phenomenon takes place if the node of the amplitude of radial displacement coincides with the boundary of the mixed core. In this case the core can be regarded as a driving generator of the oscillations, determining their period and phase. It is suggested as the explanation of the observational properties of the 160-min oscillation.
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