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1.
Collinear libration points play an important role in deep space exploration because of their special positions and dynamical characteristics. Since motion around them is unstable, we need to control the spacecraft if we wish to keep them around such a libration point for a long time. Here we propose a continuous low-thrust control strategy, illustrated with numerical simulations combined with the orbit design and control of the World Space Observatory/UltraViolet (WSO/UV).  相似文献   

2.
Quasi-simultaneous VLBI observations at 15-86 GHz have shown that in the classical superluminal radio source 3C 273, the spectral index α(Sv∝v^α) has a systematic variation along the jet. For epoch 1995.15, a spectral reversal was observed at core distance -1.5mas, where the superluminal knot C12 Located. Similarly, for epoch 1997.18, two spectral reversals wrer observed at core distances of -1.8 mas and -4.2 mas ,where superluminal knots C11 and C14 were, respectively. These spectral reversals are associated with local maxima of the jet width. We suggest that this phenomenon may be related to a stratification of the jet structure, i.e., its physical parameters (flow velocity, Doppler factor, electron density and energy, magnetic field strength,etc.) are substantially dependent on the distance from the jet axis. These properties may be naturally formed through gasdynamic processes when the jet expands into a lower pressure ambient medium.  相似文献   

3.
We have pointed out that, when thermal relativistic electrons with an isotropic velocity distribution move through a region of dense gas or impinge upon its surface, the Cerenkov effect will produce a particular kind of atomic or ionic emission line, which we have called the “Cerenkov line-like radiation”. This prediction for the optical wavebands has been verified by laboratory experiments. In this paper, we extend this line-like radiation theory to the X-ray waveband and give the basic formulae for calculating the intensity ratio and intrinsic redshift ratio of the Cerenkov iron Kα and Kβ lines, for different ionization orders of iron. Potential application of this calculated result may be found in the study of AGNs. The recent observations of NGC3783 show that besides the iron Kα line at ∼6.4 keV, there is also a very strong iron Kβ line at ∼7.0 keV, and that the ratio of equivalent widths between the two is anomalous: EWKα/EWKβ ≈ 3.43. It is difficult to explain this by the conventional mechanism of “photoelectric absorption-fluorescence emission”. We suggest that the mechanism of Cerenkov line-like radiation can provides a way of solving this puzzle. Besides, we expect that the calculated intrinsic redshift ratio of Cerenkov iron Kα and Kβ lines could be tested in future observations. If our suggestion is further supported by observations, then our view on the physical environment around the central massive black hole of an AGN will be greatly modified: the activity becomes more energetic and violent, and the gas, much denser than previously thought.  相似文献   

4.
Magnetic clouds (MCs) have been identified for the period 2007??C?2009 (at/near the recent solar minimum) from Wind data, then confirmed through MC parameter fitting using a force-free model. A dramatic increase in the frequency of occurrence of these events took place from the two early years of 2007 (with five MCs) and 2008 (one MC) compared to 2009 (12 MCs). This pattern approximately mirrors the occurrence-frequency profile that was observed over a three-year interval 12 years earlier, with eight events in 1995, four in 1996, and 17 in 1997, but decreased overall by a factor of 0.62 in number. However, the average estimated axial field strength [??|B O|??] taken over all of the 18 events of 2007??C?2009 (called the ??recent period?? here) was only 11.0 nT, whereas ??|B O|?? for the 29 events of 1995??C?1997 (called the ??earlier period??) was 16.5 nT. This 33% average drop in ??|B O|?? is more or less consistent with the decreased three-year average interplanetary magnetic field intensity between these two periods, which shows a 23% drop. In the earlier period, the MCs were clearly of mixed types but predominantly of the South-to-North type, whereas those in the recent period are almost exclusively the North-to-South type; this change is consistent with global solar field changes predicted by Bothmer and Rust (Geophys. Monogr. Ser. 99, 139, 1997). As we have argued in earlier work (Lepping and Wu, J. Geophys. Res. 112, A10103, 2007), this change should make it possible to carry out (accurate short-term) magnetic storm forecasting by predicting the latter part of an MC from the earlier part, using a good MC parameter-fitting model with real-time data from a spacecraft at L1, for example. The recent set??s average duration is 15.2 hours, which is a 27% decrease compared to that of the earlier set, which had an average duration of 20.9 hours. In fact, all physical aspects of the recent MC set are shown to drop with respect to the earlier set; e.g., as well as the average internal magnetic field drop, the recent set had a somewhat low average speed of 379 km?s?1 (5% drop), and the average diameter had a 24% drop. Hence, compared to the earlier set, the recent set consists of events that are smaller, slightly slower, and weaker in every respect (and fewer in number), but in a relative sense the two three-year sets have similar frequency-of-occurrence profiles. It is also interesting that the two sets have almost the same average axial inclinations, i.e., axial latitude ??31° (in GSE). These MC characteristics are compared to relevant solar features and their changes. A preliminary assessment of the statistics on possible shocks and pressure pulses upstream of these recent MCs yields the following: About 28% of the MCs, at most, had shocks, and 33% had shocks and/or pressure pulses. These are low values, since typically the percentage of cases with shocks is about 50%, and the percentage with shocks and/or pressure pulses is usually about 75%.  相似文献   

5.
High dispersion CCD spectra are used to study the profiles of the Hα and Hβ lines of 48 stars in early spectral classes in the young diffuse binary cluster h/χ Per. In addition, moderate resolution spectra of 15 B and Be stars were taken over the interval 4400–4960 Å. One or, possibly, two new Be stars are discovered. The major parameters of the Hα line are measured for the observed B and Be stars. The spectra over 4400–4960 Å are used to estimate Teff, logg, and υsin i. No traces of emission are detected in the Hα line profiles for 28 of the stars and emission is observed in the Hα line for 20. During our observations an absorption profile of the Hα line was observed for some of the stars, such as Oo146, Oo566, Oo922, and Oo1268, although they have previously been identified as Be stars. A significant long-term variability of the Hα line is discovered for the Be stars Oo1161 and Oo2242. Oo2371 manifests a variability in its faint emission spectrum which is typical of close binary systems that include a Be star. __________ Translated from Astrofizika, Vol. 51, No. 2, pp. 305–319 (May 2008).  相似文献   

6.
This paper explores the correlation between the fractional variation of the ionizing continuum and CⅣ broad absorption lines(BALs) with different ionization levels.Our results reveal anti-correlations between fractional variation of the continuum and fractional equivalency width(EW) variation of the C Ⅳ B ALs without AlⅢ B AL/mini-BALs at corresponding velocities,providing evidence for the widespread influence of the ionizing continuum variability on the variation of HiBALs.Conversely,for CⅣ BAL...  相似文献   

7.
We have analysed the wide band images taken by Hinode/SOT, in a blue continuum window and in the G-band, more or less on a daily basis in the frame of the synoptic program, to investigate the variation of the solar granulation and of the photospheric network with the activity cycle. A particular attention has been given to disentangle solar effects from instrumental ones. It appears that a substantial fraction of the images are more or less blurred and/or defocussed. During the analysed period November 2006??C?July 2010, the granulation contrast of the sharpest selected images decreased steadily, the granulation scale increased and the number of MBPs decreased (they are the Bright Points of Magnetic origin which form the photospheric network in G-band images). These trends are likely of instrumental origin. Consequently, the granulation and the photospheric network have most probably not changed during the extended solar minimum 2007??C?2009.  相似文献   

8.
In this paper, we discuss the fundamental aspects of the semi-analytical precession–nutation models that were adopted by IAU Resolutions in 2000 and 2006. We show that no significant discrepancies appear between those models (Mathews et al., J Geophys Res 107:B4, ETG 3-1–3-26, 2002, Capitaine et al., Astron Astrophys 412:567– 586, 2003) and other semi-analytical solutions or the INPOP06 numerical integration (Fienga et al., Astron Astrophys 477:315–327, 2008), especially for the quadratic terms. We also report on the most recent comparisons of the models with VLBI observations. We have employed different empirical models to fit the residuals, in attempting to characterize the nature of the observed curvature. The efficiencies of those empirical models are compared and their interpretations in terms of physical mechanisms are discussed. We show that a combination of linear and 18.6-year corrections is the most credible model for explaining the currently observed residuals, but that a longer span of observations is required before the true character of the effect can be determined. We note that the predictions from the ERA-2005 theory (Krasinsky, Celest Mech Dyn Astron 96:169–217, 2006) have diverged from recent VLBI results and suggest that the empirical nature of the ERA model is responsible.  相似文献   

9.
We construct for the first time, the sequences of stable neutron star (NS) models capable of explaining simultaneously, the glitch healing parameters, Q, of both the pulsars, the Crab (Q≥0.7) and the Vela (Q≤0.2), on the basis of starquake mechanism of glitch generation, whereas the conventional NS models cannot give such consistent explanation. Furthermore, our models also yield an upper bound on NS masses similar to those obtained in the literature for a variety of modern equations of state (EOSs) compatible with causality and dynamical stability. If the lower limit of the observational constraint of (i) Q≥0.7 for the Crab pulsar and (ii) the recent value of the moment of inertia for the Crab pulsar (evaluated on the basis of time-dependent acceleration model of the Crab Nebula), I Crab,45≥1.93 (where I 45=I/1045 g cm2), both are imposed together on our models, the models yield the value of matching density, E b =9.584×1014 g cm−3 at the core-envelope boundary. This value of matching density yields a model-independent upper bound on neutron star masses, M max≤2.22M ⊙, and the strong lower bounds on surface redshift z R ≃0.6232 and mass M≃2.11M ⊙ for the Crab (Q≃0.7) and the strong upper bound on surface redshift z R ≃0.2016, mass M≃0.982M ⊙ and the moment of inertia I Vela,45≃0.587 for the Vela (Q≃0.2) pulsar. However, for the observational constraint of the ‘central’ weighted mean value Q≈0.72, and I Crab,45>1.93, for the Crab pulsar, the minimum surface redshift and mass of the Crab pulsar are slightly increased to the values z R ≃0.655 and M≃2.149M ⊙ respectively, whereas corresponding to the ‘central’ weighted mean value Q≈0.12 for the Vela pulsar, the maximum surface redshift, mass and the moment of inertia for the Vela pulsar are slightly decreased to the values z R ≃0.1645, M≃0.828M ⊙ and I Vela,45≃0.459 respectively. These results set an upper and lower bound on the energy of a gravitationally redshifted electron-positron annihilation line in the range of about 0.309–0.315 MeV from the Crab and in the range of about 0.425–0.439 MeV from the Vela pulsar.  相似文献   

10.
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11.
X-ray and γ-ray observations can help understand the origin of the electron and positron signals reported by ATIC, PAMELA, PPB-BETS, and Fermi. It remains unclear whether the observed high-energy electrons and positrons are produced by relic particles, or by some astrophysical sources. To distinguish between the two possibilities, one can compare the electron population in the local neighborhood with that in the dwarf spheroidal galaxies, which are not expected to host as many pulsars and other astrophysical sources. This can be accomplished using X-ray and γ-ray observations of dwarf spheroidal galaxies. Assuming the signal detected by Fermi and ATIC comes from dark matter and using the inferred dark matter profile of the Draco dwarf spheroidal galaxy as an example, we calculate the photon spectrum produced by electrons via inverse Compton scattering. Since little is known about the magnetic fields in dwarf spheroidal galaxies, we consider the propagation of charged particles with and without diffusion. Extending the analysis of Fermi collaboration for Draco, we find that for a halo mass ∼109 M⊙, even in the absence of diffusion, the γ-ray signal would be above the upper limits. This conclusion is subject to uncertainties associated with the halo mass. If dwarf spheroidal galaxies host local magnetic fields, the diffusion of the electrons can result in a signal detectable by future X-ray telescopes.  相似文献   

12.
Low noise photoelectric measurements of the line profile of the g = 0 Fe line gl 5576.097 combined with determinations of the wavelength shift of its centre calibrated by use of an I 2 absorption tube are reported. Measurements taken at various limb distances (1.0 cos 0.2) and along 4 different diameters of the Sun are used to investigate the behaviour of the line asymmetry (C-shape) and wavelength shift of the line centre as functions of cos and of latitude and to search for possible pole-equator differences.An accuracy of approx. 0.8 mÅ r.m.s. is achieved for the determination of the centre of the solar line relative to the iodine lines and of 0.3 mÅ to 1 mÅ r.m.s. for the relative variations of the C-shape. The analysis shows a significant difference between the limb-effect curves along polar and equatorial diameters for cos 0.4 and changes of the C-shape for 0.9 cos 0.6 with a rather strong indication of a latitude dependence of the C-shape. This latitude dependence may account for the so-called ears observed by Howard et al. (1980) who used the well-known Doppler compensator method which integrates the line asymmetry from the line wings to the core.Mitteilungen aus dem Kiepenheuer-Institut Nr. 207.  相似文献   

13.
The demonstration of a compact imaging X-ray spectrometer (D-CIXS), which flew on ESA's SMART-1 mission to the Moon (Racca et al., 2001; Foing et al., 2006), was designed to test innovative new technologies for orbital X-ray fluorescence spectroscopy. D-CIXS conducted observations of the lunar surface from January 2005 until SMART-1 impacted the Moon in September 2006. Here, we present scientific observations made during two solar flare events and show the first detection of Titanium Kα from the lunar surface. We discuss the geological implications of these results. We also discuss how experience from D-CIXS has aided the design of a similar instrument (Chandrayaan-1 X-ray Spectrometer (C1XS)) that was launched on the 22nd October 2008 on India's Chandrayaan-1 mission to the Moon.  相似文献   

14.
The photometric variability of CPD-48°1577 in the optical and IR ranges is discussed. The structure and variation of prominent emission line profiles are investigated. An estimate of the distance is given.Paper presented at the Lembang-Bamberg IAU Colloquium No 80 on Double Stars: Physical Properties and Generic Relations, held at Bandung, Indonesia, 3–7 June, 1983.Based on data collected at the European Southern Observatory in Chile.  相似文献   

15.
There are numerous complex organic molecules containing carbon and oxygen atoms which show either C–C–O or C–O–C bonding backbone. This paper examines altogether 51 C–C–O and C–O–C bonding backbone molecules from ten different isomeric groups (C2H2O, C3H2O, C2H4O, C2H4O2, C3H4O, C2H6O, C2H6O2, C3H6O, C3H6O2, C3H8O) to summarize the present astronomical status of these molecules. Accurate calculations of enthalpy of formation of these molecules show that the isomers with C–C–O backbone are more stable than the C–O–C backbone. Interestingly, a detailed analysis of relevant astromolecules indicates that most of the observed astromolecules have the C–C–O backbone. As a matter of fact, of all the molecules examined in this study, 80% of the astronomically observed species have the C–C–O backbone while only 20% have the C–O–C backbone. In general, interstellar abundance of a molecule is controlled by some factors such as kinetics, formation and destruction pathways,thermodynamics etc. A proper consideration of these factors could explain the observed abundances of these molecules. All these possible key factors are discussed in this paper.  相似文献   

16.
Using observations from the High Energy Telescopes (HETs) on the STEREO A and B spacecraft and similar observations from near-Earth spacecraft, we summarize the properties of more than 200 individual >?25 MeV solar proton events, some detected by multiple spacecraft, that occurred from the beginning of the STEREO mission in October 2006 to December 2013, and provide a catalog of these events and their solar sources and associations. Longitudinal dependencies of the electron and proton peak intensities and delays to onset and peak intensity relative to the solar event have been examined for 25 three-spacecraft particle events. Expressed as Gaussians, peak intensities fall off with longitude with σ=47±14° for 0.7?–?4 MeV electrons, and σ=43±13° for 14?–?24 MeV protons. Several particle events are discussed in more detail, including one on 3 November 2011, in which ～?25 MeV protons filled the inner heliosphere within 90 minutes of the solar event, and another on 7 March 2012, in which we demonstrate that the first of two coronal mass ejections that erupted from an active region within ～?1 hour was associated with particle acceleration. Comparing the current Solar Cycle 24 with the previous cycle, the first >?25 MeV proton event was detected at Earth in the current solar cycle around one year after smoothed sunspot minimum, compared with a delay of only two months in Cycle 23. Otherwise, solar energetic particle event occurrence rates were reasonably similar during the rising phases of Cycles 23 and 24. However, the rate declined in 2013, reflecting the decline in sunspot number since the peak in the northern-hemisphere sunspot number in November 2011. Observations in late 2013 suggest that the rate may be rising again in association with an increase in the southern sunspot number.  相似文献   

17.
Supergranulation is a component of solar convection that manifests itself on the photosphere as a cellular network of around 35 Mm across, with a turnover lifetime of 1 – 2 days. It is strongly linked to the structure of the magnetic field. The horizontal, divergent flows within supergranule cells carry local field lines to the cell boundaries, while the rotational properties of supergranule upflows may contribute to the restoration of the poloidal field as part of the dynamo mechanism, which controls the solar cycle. The solar minimum at the transition from cycle 23 to 24 was notable for its low level of activity and its extended length. It is of interest to study whether the convective phenomena that influence the solar magnetic field during this time differed in character from periods of previous minima. This study investigates three characteristics (velocity components, sizes and lifetimes) of solar supergranulation. Comparisons of these characteristics are made between the minima of cycles 22/23 and 23/24 using MDI Doppler data from 1996 and 2008, respectively. It is found that whereas the lifetimes are equal during both epochs (around 18 h), the sizes are larger in 1996 (35.9 ± 0.3 Mm) than in 2008 (35.0 ± 0.3 Mm), while the dominant horizontal velocity flows are weaker (139 ± 1 m s−1 in 1996; 141 ± 1 m s−1 in 2008). Although numerical differences are seen, they are not conclusive proof of the most recent minimum being inherently unusual.  相似文献   

18.
In this paper we explore the consequences of the recent determination of the mass m=(8.7±0.8)M ⊙ of Cygnus X-1, obtained from the Quasi-Periodic Oscillation (QPO)-photon index correlation scaling, on the orbital and physical properties of the binary system HDE 226868/Cygnus X-1. By using such a result and the latest spectroscopic optical data of the HDE 226868 supergiant star we get M=(24±5)M ⊙ for its mass. It turns out that deviations from the third Kepler law significant at more than 1-sigma level would occur if the inclination i of the system’s orbital plane to the plane of the sky falls outside the range ≈41–56 deg: such deviations cannot be due to the first post-Newtonian (1PN) correction to the orbital period because of its smallness; interpreted in the framework of the Newtonian theory of gravitation as due to the stellar quadrupole mass moment Q, they are unphysical because Q would take unreasonably large values. By conservatively assuming that the third Kepler law is an adequate model for the orbital period we obtain i=(48±7) deg which yields for the relative semimajor axis a=(42±9)R ⊙ (≈0.2 AU).  相似文献   

19.
When the interplanetary parameter ε(= VB2 sin4 (θ2)l02) exceeds the amount that can be dissipated by the ionosphere in terms of the Joule heat production, the excess energy is absorbed by the ring current belt, resulting in abnormal growth of the Dst index.  相似文献   

20.
The infrared emission observed for dust in the Trapezium nebula over the waveband 8–40 m cannot be explained on the basis of a simple silicate model involving either terrestrial or lunar silicates. Laboratory measurements were carried out to determine the opacity coefficient of finely crushed Murchison meteorite material. Murchison material (including organics within it) provides a better fit to the Trapezium data than any known silicate, but the agreement is inferior to that obtained for a diatom model.  相似文献   

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