在18及6厘米波长对4C 39.25的VLBI观测

在18及6厘米,以基线长分别达15及23兆波长的欧洲长基线干涉网(EVN),对类星体4C 39.25作了VLBI观测,试图搜寻该类星体的中等尺度——10到100毫角秒(mas)的结构。 观测未曾检测到这种尺度上超过核峰值亮度5％的明显结构。但核自身看来有2到4毫角秒的延伸,而且其流量可变。     

VLBI observations of 4C 39.25 at 18 and 6 cm waves

VLBI observations at wavelengths of 18 and 6 cm with baselines up to 15 and 23 million wavelengths have been made in a search for structures on scales of 10 to 100 milliarcseconds (mas) in the quasar 4C 39.25.No significant structure on these scales above 5% of the peak brightness was detected. The core itself, however, appears to be extended on a scale of 2 to 4 mas and to have a variable flux.     

百秒差距尺度上的4C39.25

通过主要在短厘米波长的全球VLBI观测,已经发现强射电类星体4C39.25在十秒差距尺度结构中的视超光速运动,其运动学图景表明该源是一个很特殊的视超光速源.近几年已提出了若干模型,试图解释这特殊的运动图景.报道不多的百秒差距尺度的VLBI观测,很可能有助于检验提出的模型.本文介绍用欧洲网及上海25m天线,在18cm波长对4C39.25所作的VLBI 成象观测的初步结果,显示百秒差距尺度复杂结构及可能存在的视超光速运动.     

Noble gases in presolar diamonds I: Three distinct components and their implications for diamond origins

Abstract— High-purity separates of presolar diamond were prepared from 14 primitive chondrites from 7 compositional groups. Their noble gases were measured using stepped pyrolysis. Three distinct noble gas components are present in diamonds, HL, P3, and P6, each of which is found to consist of five noble gases. P3 , released between 200 °C and 900 °C, has a “planetary” elemental abundance pattern and roughly “normal” isotopic ratios. HL , consisting of isotopically anomalous Xe-HL and Kr-H, Ar with high ³⁸Ar/³⁶Ar, and most of the gas making up Ne-A2 and He-A, is released between 1100 °C and 1600 °C. HL has “planetary” elemental ratios, except that it has much more He and Ne than other known “planetary” components. HL gases are carried in the bulk diamonds, not in some trace phase. P6 has a slightly higher median release temperature than HL and is not cleanly separated from HL by stepped pyrolysis. Our data suggest that P6 has roughly “normal” isotopic compositions and “planetary” elemental ratios. Both P3 and P6 seem to be isotopically distinct from P1, the dominant “planetary” noble-gas component in primitive chondrites. Release characteristics suggest that HL and P6 are sited in different carriers within the diamond fractions, while P3 may be sited near the surfaces of the diamonds. We find no evidence of separability of Xe-H and Xe-L or other isotopic variations in the HL component. However, because ～10¹⁰ diamonds are required to measure a Xe composition, a lack of isotopic variability does not constrain diamonds to come from a single source. In fact, the high abundance of diamonds in primitive chondrites and the presence of at least three distinct noble-gas components strongly suggest that diamonds originated in many sources. Relative abundances of noble-gas components in diamonds correlate with degree of thermal processing (see companion paper), indicating that all meteorites sampled essentially the same mixture of diamonds. That mixture was probably inherited from the Sun's parent molecular cloud.     

Neue Bestimmungen der Präzession nach dem Prinzip der Maximalmenge von Sternen ohne meßbare Eigenbewegung

The principle of the maximum set of stars without proper motions (μ = 0) requires that the corrections of the precession be specified so that the number of the stars “without proper motion” (practically μ < 0″.10) becomes a maximum. These stars are named the “Träger” (carriers) of the non-rotating coordinate system. The method avoids any hypothesis about the distribution of the proper motions and hence does not use the method of least squares. The procedure algorithmized in the FORTRAN language and computed on a UNIVAC 1108 is based on the geometric means of a regular sequence of numbers of stars within concentric circles around the position μ = 0 with growing radius in a rightangle coordinate system with the axes μαcos δ and μδ. The main concept is the “zero-point density” D in the defining equation (13). The inequality (15) is the main relation of the method, where r is the radius of a circle-neighbourhood of the position μ = 0. The main part of the procedure in praxi and the algorithm are described in section 5. In sections 6, 7 and 8 the method is applied to the proper motions of the catalogue FK₄, then to the proper motions of the catalogue N₃₀ and finally to a third catalogue, which consists of the proper motions of N₃₀ reduced to the system of FK₄ (N₃₀ → FK₄). The main result lies in table 4 of section 9. With regard to the accuracy as well as to the number of the “Träger” (carriers) of the coordinate system free of rotation the results from (N₃₀ → FK₄) have the following implications: the corrections of lunisolar precession Δp₁ = +0″.97 ± 0″.04 per century; the correction of the motion of equinox Δp₂ = Δλ + Δc = +1″.10 ± 0″.04 per century. For the motion of equinox Δp₂ = Δλ + Δc = +1″.10 ± 0″.04 per century. For the purpose of investigations of motions of stars these corrections correspond to the corrections (21) of the proper motions of N₃₀ → FK₄. The new method has the advantage also, that fewer than half of the stars of a catalogue can influence the result (table 6).     

A VLBI Study of Compact Steep Spectrum Sources 3C43, 3C48 and 3C454

We used the VLBA(NRAO, USA) and made VLBI observations towards the compact steep spectrum sources 3C43, 3C48 and 3C454 at the central frequency 1.6 GHz, and obtained their total flux density maps and information on the structures of their components. By comparison with the previous data, we analyzed the variations of their flux densities as well as the displacements of their components. It is found that the total flux density of the source 3C43, as well as the flux densities and relative positions of its components are quite stable in 14 years. For the source 3C454, the total flux density and the flux densities of its components are also relatively stable, but two of the components moved away from the central core with superluminal velocities of 21.6c and 17.7c. Fitted to their flux densities at 4 L-band frequencies, the spectral indexes of the sources 3C43 and 3C454 were obtained to be 0.63 and 0.86, respectively, in good agreement with previous results, and consistent with the definition of α ≥0.5 for compact steep spectrum sources.     

Empirical Modeling of Radiative <Emphasis Type="Italic">versus</Emphasis> Magnetic Flux for the Sun-as-a-Star

We study the relationship between full-disk solar radiative flux at different wavelengths and average solar photospheric magnetic-flux density, using daily measurements from the Kitt Peak magnetograph and other instruments extending over one or more solar cycles. We use two different statistical methods to determine the underlying nature of these flux – flux relationships. First, we use statistical correlation and regression analysis and show that the relationships are not monotonic for total solar irradiance and for continuum radiation from the photosphere, but are approximately linear for chromospheric and coronal radiation. Second, we use signal theory to examine the flux – flux relationships for a temporal component. We find that a well-defined temporal component exists and accounts for some of the variance in the data. This temporal component arises because active regions with high magnetic-field strength evolve, breaking up into small-scale magnetic elements with low field strength, and radiative and magnetic fluxes are sensitive to different active-region components. We generate empirical models that relate radiative flux to magnetic flux, allowing us to predict spectral-irradiance variations from observations of disk-averaged magnetic-flux density. In most cases, the model reconstructions can account for 85 – 90% of the variability of the radiative flux from the chromosphere and corona. Our results are important for understanding the relationship between magnetic and radiative measures of solar and stellar variability.     

Japanese VLBI Network Observations of a Gamma-Ray Narrow-Line Seyfert 1 Galaxy 1H 0323+342

We made simultaneous single-dish and VLBI observations of a gamma-ray narrow-line Seyfert 1 (NLS1) galaxy 1H 0323+342. We found significant flux variation at 8 GHz on a time scale of one month. The total flux density varied by 5.5% in 32 days, corresponding to a variability brightness temperature of 7.0 × 10¹¹ K. We also obtained brightness temperatures of greater than 5.2 × 10¹⁰ K from the VLBI images. These high brightness temperatures suggest that the source has nonthermal processes in the central engine. The source structure could be modelled by two elliptical Gaussian components on the parsec scales. The flux of the central component decreases in the same way as the total flux density, showing that the short-term variability is mainly associated with this component.     

The Self-Inversion of the Sign of Circular Polarization in “Halo” Microwave Sources

The large active region AR NOAA 5200 from October 1988 is used to investigate the concept of the “halo,” a magnetosphere-like structure above the active region. This structure is studied by using radio spectral polarization observations with high spatial resolution obtained mainly with the radio telescope RATAN-600. In the case of AR 5200 the halo emission accounted for >50% of the total AR emission. The results of the analysis of the observational data and of the model calculations allow us to reach the following conclusions: (1) The halo is a large, nonstructured, source of emission with a size of the total AR, with the emission centered at the dividing (neutral) line of polarities of the bipolar sunspot group. (2) The emission spectrum allows us to distinguish two components: a thermal part and a nonthermal part. The presence of two components implies that there are two populations of particles with different energy levels in the emission region. The phenomenon of inversion of the polarized halo radio emission could be explained by the influence of propagation conditions inside the source. The term “self-inversion” is introduced. The maximum in the halo density flux spectrum at wavelengths of 5 –10 cm may be explained by scattering resulting from the strong suppression of the emissivity of nonthermal electrons at these and longer wavelengths.     

The unusual 2006 dwarf nova outburst of GK Persei

The 2006 outburst of GK Persei differed significantly at optical and ultraviolet (UV) wavelengths from typical outbursts of this object. We present multiwavelength (X-ray, UV and optical) Swift and AAVSO data, giving unprecedented broad-band coverage of the outburst, allowing us to follow the evolution of the longer-than-normal 2006 outburst across these wavelengths. In the optical and UV we see a triple-peaked morphology with maximum brightness ∼1.5 mag lower than in previous years. In contrast, the peak hard X-ray flux is the same as in previous outbursts. We resolve this dichotomy by demonstrating that the hard X-ray flux only accounts for a small fraction of the total energy liberated during accretion, and interpret the optical/UV outburst profile as arising from a series of heating and cooling waves traversing the disc, caused by its variable density profile.     

Thermal protons in the morning magnetosphere: Filling and heating near the equatorial plasmapause

Thermal H⁺ distributions have been measured as the European Space Agency GEOS-1 satellite passed through the late morning equatorial magnetosphere, plasmapause and plasmasphere. The unique capabilities of the on-board Supralhermal Plasma Analysers (SPA) have been used to overcome the retarding floating potential of the satellite and measure the velocity distribution of the cold protons. In the magnetosphere an enhanced source cone of such ions with a temperature of ~ 0.5 eV is a signature of the filling process occurring outside the plasmapause where flux tubes are relatively empty. In the plasmasphere the thermal H⁺ is essentially isotropic with a temperature less than 0.5 eV but the motion of the satellite introduces apparent drift.These measurements of cold proton velocity distribution now permit a reappraisal of the definition of the “plasmapause”. It becomes inappropriate to use an arbitrary empirical density, e.g. the conventional 10 cm ^?3, in order to establish a boundary. It is now possible to identify a plasmapause interaction region where the two cold proton populations co-exist. This region generally lies Earthward of the 10 cm ^?3 density level, has a width which is strongly dependent on magnetic activity and the temperature is typically between 0.5 and 1.5 eV. The change from “filled” to “unfilled” flux tubes relates to the physical processes which are occurring and the controlling electric field configuration; in particular, the last closed equipotential. Throughout this region, in going from the plasmasphere to the magnetosphere, the plasma drift motion is expected to change from corotation to a convection which is controlled by E ×B, and is predominantly Sunward due to the dawn-dusk electric field. Crossing the plasmapause on the morning side, little change in drift direction should occur but subtle variations in the ionic velocity distribution do reflect the change in the degree of flux tube density equilibrium.Our first direct measurement of the magnetospheric E × B drift has been reported previously but here measurements from a selected six day period show how the plasma in the plasmapause region responds to changing magnetospheric activity. The drift velocities cannot he derived with high accuracy but the analysis shows that the technique can provide a valid mapping of the magnelospheric electric field. In addition, since the magnetospheric cold plasma distribution is observed after it has come from the ionosphere, a distance of many Earth radii, the scattering and accelerating mechanisms along the flux tube can be studied. For this particular data-set taken in the late morning, the maximum potential drops along the flux tubes were less than a volt. The ionospheric proton source cone is observed to be broad, pitch angle scattering persists up to 40 or even 70°.Although these results throw new light on the plasmaspheric filling process one must recognise that, however the plasmapause is defined, it is not a simple matter to map this boundary from the equatorial plane down to low altitudes and the mid-latitude trough.     

The UV environment of the Beagle 2 landing site: detailed investigations and detection of atmospheric state

December 25th 2003 will see the Beagle 2 lander arrive at the surface of Mars in the Isidis region, allowing for the first time in situ measurements of ultraviolet (UV) flux directly from the surface of Mars through the use of a sensor designed as part of a miniaturised environmental package. The expected conditions the sensor will experience are studied here, and the detection signatures for phenomenon such as dust devils, H₂O clouds ands near-surface fogs are presented. The beginning and end of mission surface fluxes show little variation, though the period towards mid-nominal mission does experience a maximum in total daily dose levels. Diurnal profiles are calculated highlighting the effects of increased scattering towards shorter wavelengths. A possible dust storm scenario is presented, and the effect upon component UV fluxes is shown to reverse the relative contributions of direct and diffuse components of the total UV flux. The presence of cloud formation above the landing site will be detectable though the observation of elevated diffuse/direct flux ratios. Near-surface morning fogs show a characteristic ‘dip’ in the morning profile when compared to clear mornings, allowing their detection on cloud-free mornings through post-event analysis of long term data. Predicted Phobos eclipses are investigated at each of the sensor centre wavelengths, and show greatest reduction in relative intensity at short wavelengths. Observations of near-miss eclipse events will also be possible, through monitoring of the diffuse UV flux. Dust devil encounters are shown to create a double minima lightcurve, with the depth of the minima dependent upon the total dust loading of the vortex. The effects of these changing conditions on DNA-weighted irradiances are investigated. Possible dust storms provide the greatest increase in biological protection, whereas expected cloud formations at the Beagle 2 site are found to offer negligible protection. Within just five minutes of landing >95% of any Bacillus subtilis-like bacteria present on the surface of the craft will have lost viability.     

致密陡谱源3C43、3C48和3C454的VLBI研究

利用美国甚长基线阵对3个致密陡谱源3C43、3C48和3C454进行中心频率1.6GHz的观测,获得总流量图和各个子源的结构等信息.对比已有的数据,分析源3C43和3C454的流量变化和各个子源的位置移动,发现3C43的总流量、各子源流量、各子源的相对位置在14年内比较稳定;3C454的总流量和各子源流量也比较稳定,但两个子源相对核心的偏离速度分别是光速的21.6和17.7倍,存在明显的视超光速现象.同时通过对L波段4个频率的总流量结果进行谱指数拟合,获得源3C43和3C454的谱指数分别是0.63和0.86,符合致密陡谱源谱指数α≥0.5的定义,也与已有的结果吻合较好.     

Rigorous computation of proper motions and their effects on star positions

New rigorous formulas are given for the computation of the effects of proper motions and radial velocities on star positions, and for the transformation of proper motion components and radial velocities from one epoch to another. These expressions depend explicitly only on the values of the star's coordinates and distance, proper motion components and radial velocity, at the initial epoch.     

Reverse-current effect in present-day models of solar flares: Theory and high-accuracy observations

We propose an accurate analytical model for the source of hard X-ray emission from a flare in the form of a “thick target” with a reverse current to explain the results of present-day observations of solar flares onboard the GOES, Hinode, RHESSI, and TRACE satellites. The model, one-dimensional in coordinate space and two-dimensional in velocity space, self-consistently takes into account the fact that the beam electrons lose the kinetic energy of their motion along the magnetic field almost without any collisions under the action of the reverse-current electric field. Some of the electrons return from the emission source to the acceleration region without losing the kinetic energy of their transverse motion. Based on the observed hard X-ray bremsstrahlung spectrum, the model allows the injection spectrum of accelerated electrons to be reconstructed with a high accuracy. As an example, we consider the white-light flare of December 6, 2006, which was observed with a high spatial resolution in the optical wavelength range at the main maximum of hard X-ray emission. Within the framework of our model, we show that to explain the hard X-ray spectrum, the flux density of the energy transferred by electrons with energies above 18 keV was ～3 × 10¹³ erg cm^?2 s^?1. This exceeds the habitual values typical of the classical model of a thick target without a reverse current by two orders of magnitude. The electron density in the beam is also very high: ～10¹¹ cm^?3. A more careful consideration of plasma processes in such dense electron beams is needed when the physical parameters of a flare are calculated.     

The brightness temperatures of Saturn and its rings at 39 microns

We have resolved the relative rings-to-disk brightness (specific intensity) of Saturn at 39 μm (δλ ? 8 μm) using the 224-cm telecscope at Mauna Kea Oservatory, and have also measured the total flux of Saturn relative to Jupiter in the same bandpass from the NASA Learjet Observatory. These two measurements, which were made in early 1975 with Saturn's rings near maximum inclination (b′ ? 25°), determine the disk and average ring (A and B) brightness in terms of an absolute flux calibration of Jupiter in the same bandpass. While present uncertainties in Jupiter's absolute calibration make it possible to compare existing measurementsunambiguously, it is nevertheless possible to conclude the following: (1) observations between 20 and 40 μm are all compatible (within 2σ) of a disk brightness temperature of 94°K, and do not agree with the radiative equilibrium models of Trafton; (2) the rings at large tilt contribute a flux component comparable to that of the planet itself for λ ? 40 μm and (3) there is a decrease of ～22% in the relative ring: disk brightness between effective wavelengths of 33.5 and 39 μm.     

Dynamics of artificial plasma clouds in “SPOLOKH“ experiments : Cloud deformation

Data on the evolution of the density profiles of the neutral and ionized components of barium clouds obtained in “Spolokh” experiments are presented. The ion density in the cigar-like structure exceeds by more than an order of magnitude that of the background plasma, while the density in the plasma tail out flowing from the cigar-like structure is of the same order as that of the background plasma. The Ba⁺ outflow rate is determined. The results agree with observed cloud motion and with the estimates following from Dzubenko et al. (1983).     

Frequency analysis of photometric observations of HD 101158

Observations of solar radio emission at 3 cm wavelength have been made at Japal-Rangapur Observatory for 1980–1981, the solar maximum year using the 3 m radio telescope. The correlation between microwave solar emissions and the sunspot activity on monthly basis has been found to be high during the maximum phase and in the high cm wavelength band. The basic component has been estimated statistically for successive solar rotations using the data obtained at Japal-Rangapur Observatory. Further, this was compared with the data obtained at other cm wavelengths during 1980–1981 and the solar minimum period 1975–1976 of the 21st cycle. The comparison showed pronounced dips in flux levels at different wavelengths during the summer months of the solar maximum year which may be attributed to the presence of coronal holes in the various levels of the solar atmosphere. The computed basic component values showed pronounced variation at high cm wavelengths for the solar maximum period with dissimilar variations at different wavelengths. During the solar minimum period the variations were negligibly small and showed more or less constant level of activity.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984.     

22周上升段太阳射电缓变成分的一些统计特性

本文根据1987年1月—1989年11月期间,2cm、3.4cm、6cm、10.7cm和21.2cm五个波段每日总辐射流量与日面上占主导地位的活动区黑子视面积之间的关系,对第22周上升段若干大活动区的射电缓变成分的统计特性进行了分析研究,发现有几个大活动区在日面时S-Ay图上处在平均曲线之下,当黑子面积增加时,射电流量的增加并不明显。     

Supermassive black-hole binary systems in active galactic nuclei

An analysis of periodic components of flux variability was carried out based on the long-term monitoring of the nuclei of active galaxies 3C454.3, 1633+382, and 3C120, performed in the Crimean Astrophysical Observatory from 1985 to 2008 at 22.2 and 36.8 GHz. Long-period components of the variability (12–14 yrs) were detected and interpreted in terms of the precessional motion of the central body in binary systems. Short-period components (1.5–3 yrs) related to the orbital periods for the motions of the central supermassive black holes were also detected. We concluded that the brightest active galaxies observed as nonstationary sources in a wide range of wavelengths are binary systems of supermassive black holes at the stage of evolution close to coalescence. For the supposed binary black-hole systems, the masses of the central objects and their companions, the orbital radii of the companions, and the coalescence times were determined. The ratios of the masses in the binary systems in all cases proved to be less than ten, pointing to a strong gravitational effect of the companion on the central black hole. The velocities of the central body motion proved to be high, approximately 1000 km/s. This fact should be accounted for in the calculations of the rate of accretion onto the central body. The orbital radii of the companions fall into a narrow range between 4 × 10¹⁶ cm and 6 × 10¹⁶ cm, demonstrating a strong dependence of the masses of the binary systems on the orbital sizes and the energy loss for the gravitational radiation. Within the orbit of the companion during its motion through the accretion disk, a high temperature of surrounding gas is achieved. The high density of the medium, 10⁹–10¹⁰ cm^?3, combined with the magnetic field and shock waves propagating in the accretion disk, develop the conditions for powerful energy release in the directed jets.