共查询到20条相似文献，搜索用时 46 毫秒
1.
Superluminal Motion and Polarization in Blazars 总被引：3，自引：0，他引：3
Jun-Hui Fan Yong-Jiu Wang Jiang-He Yang Cheng-Yue Su Center for Astrophysics Guangzhou University Guangzhou Physics Institute Hunan Normal University Changsha Department of Electronics Physics Hunan University of Arts Science Chaugde Department of Physics Guangdong Industry University Guangzhou 《中国天文和天体物理学报》2004,4(6):533-540
A relativistic beaming model has been successfully used to explain the observed properties of active galactic nuclei (AGNs). In this model there are two emission components, a boosted one and an unbeamed one, shown up in the radio band as the core and lobe components. The luminosity ratio of the core to the lobe is denned as the core-dominance parameter (R = LCore/LLobe). The de-beamed radio luminosity (Ldbjet) in the jet is assumed to be proportional to the unbeamedluminosity (Lub) in the co-moving frame, i.e., f = Ldbjet/Lub, and f is determined in ourprevious paper. We further discuss the relationship between BL Lacertae objects (BLs) and flat spectrum radio quasars (FSRQs), which are subclasses of blazars with different degrees of polarization, using the calculated values of the ratio f for a sample of superluminal blazars. We found 1) that the BLs show smaller averaged Doppler factors and Lorentz factors, larger viewing angles and higher core-dominance parameters than do the FSRQs, and 2) that in th 相似文献
2.
V. A. Bronshten 《Astronomy Letters》2000,26(5):328-330
We consider the history of discovery and justify the existence in the Solar system of a new class of bodies—minicomets, i.e., bodies of cometary nature and composition but of low mass. Two classes of minicomets are distinguished: icy ones similar to the Tunguska meteorite, and snow ones, which break up at high altitudes. 相似文献
3.
K. P. Raju 《Solar physics》2009,255(1):119-129
Relative Doppler velocities and spectral linewidths in a coronal hole and in the quiet Sun region outside have been obtained from Solar and Heliospheric Observatory (SOHO)/Coronal Diagnostic Spectrometer (CDS) observations. Five strong emission lines in the CDS wavelength range (namely, O? iii 599 Å, O?v 630 Å, Ne?vi 562.8 Å, He?ii 304 Å, and Mg?ix 368 Å), whose formation temperatures represent different heights in the solar atmosphere from the lower transition region to the inner corona, have been used in the study. As reported earlier, relative velocities in the coronal hole are generally blueshifted with respect to the quiet Sun, and the magnitude of the blueshifts increases with height. It has been found that the polar coronal hole has larger relative velocities than the equatorial extension in the inner corona. Several localized velocity contours have been found mainly on network brightenings and in the vicinity of the coronal hole boundary. The presence of velocity contours on the network may represent network outflows whereas the latter could be due to localized jets probably arising from magnetic reconnection at the boundary. All spectral lines have larger widths in the coronal hole than in the quiet Sun. In O?v 630 Å an extended low-linewidth region is seen in the coronal hole?–?quiet Sun boundary, which may indicate fresh mass transfer across the boundary. Also polar coronal holes have larger linewidths in comparison with the equatorial extension. Together with larger relative velocities, this suggests that the solar wind emanating from polar hole regions is faster than that from equatorial hole regions. 相似文献
4.
A. K. Pavlov A. V. Blinov G. I. Vasil’ev M. A. Vdovina A. N. Konstantinov V. M. Ostryakov 《Astronomy Letters》2014,40(10):640-647
The production of the cosmogenic radionuclides 14C, 10Be, and 36Cl in the Earth’s atmosphere under the action of powerful impulsive proton and gamma-ray events (superpowerful solar flares and Galactic gamma-ray bursts) is considered. The possible “isotopic footprint” in natural archives (the concentrations of these isotopes in dated polar ice cores and annual tree rings) has been calculated by taking into account geophysical processes. The results obtained have been applied to analyzing the anomalous increase in the concentration of radiocarbon measured in tree rings dated 774–775 AD. Arguments for the fact that the most likely cause of this increase is the high-energy emission from a Galactic gamma-ray burst are adduced. 相似文献
5.
6.
We present a model for the general circulation and dynamical transport in Saturn’s upper troposphere and stratosphere and derive the effective advective circulation and eddy transport coefficients required for use in two-dimensional (latitude–altitude) photochemistry–transport models. A three-dimensional Outer-Planet General Circulation Model (OPGCM) is used to generate the transport data. We find that the OPGCM adequately captures the global-scale, pole-to pole temperature contrast, but overestimates mid- and high-latitude temperatures in the summer hemisphere by ～5 K. In addition, the model reproduces the local temperature minimum seen at the equator in Cassini Composite Infrared Spectrometer (CIRS) 0.1-mbar data but not the local maximum in 1-mbar temperatures, suggesting that it is capturing the phase of Saturn’s Semiannual Oscillation associated with a temperature minimum at the equator but not the opposite phase. The meridional circulation at low latitudes is found to be dominated by a seasonally reversing Hadley circulation, characterized by upwelling near the equator, cross-equatorial flow from summer to winter hemisphere, and strong subsidence centered near 25° latitude in the winter hemisphere. The cross-equatorial flow induces an asymmetry in which the equatorial jet is found to be stronger in the winter than in the summer stratosphere. The location of the subsidence near 25°N for Ls ～ 310° coincides with local maxima in acetylene, diacetylene, and methylacetylene mixing ratios measured by Cassini/CIRS (Guerlet, S., Fouchet, T., Bézard, B., Moses, J.I., Fletcher, L.N., Simon-Miller, A.A., Flasar, F.M. [2010]. Icarus 209, 682–695). This result supports the suggestion by Guerlet et al. (2010) that the hydrocarbon abundances are enhanced at this latitude by pronounced downward transport of hydrocarbon-rich air from above. The lateral eddy diffusion coefficient is found to typically be ～105–106 m2 s?1 at mid-latitudes, implying meridional eddy transport time scales of order 100–1000 years. 相似文献
7.
Yu Lu Jian-Yan WeiNational Astronomical Observatories Chinese Academy of Sciences Beijing luyu 《中国天文和天体物理学报》2003,3(5):395-409
We use controlled N-body simulation to investigate the dynamical processes (dynamical friction, tidal truncation, etc.) involved in the merging of small satellites into bigger halos. We confirm the validity of some analytic formulae proposed earlier based on simple arguments. For rigid satellites represented by softened point masses, the merging time scale depends on both the orbital shape and concentration of the satellite. The dependence on orbital ellipticity is roughly a power law, as suggested by Lacey & Cole, and the dependence on satellite concentration is similar to that proposed by White. When merging satellites are represented by non-rigid objects, Tidal effects must be considered. We found that material beyond the tidal radius are stripped off. The decrease in the satellite mass might mean an increase in the merging time scale, but in fact, the merging time is decreased, because the stripped-off material carries away a proportionately larger amount of of orbital energy and angular momentum. 相似文献
8.
P. Démoulin 《Solar physics》2009,257(1):169-184
In-situ observations of the solar wind (SW) show temperature increasing with the wind speed, whereas such a dependence is not observed
in interplanetary coronal mass ejections (ICMEs). The aim of this paper is to understand the main origin of this correlation
in the SW and its absence in ICMEs. For that purpose both the internal-energy and momentum equations are solved analytically
with various approximations. The internal-energy equation does not provide a strong link between temperature and velocity,
but the momentum equation does. Indeed, the observed correlation in the open magnetic-field configuration of the SW is the
result of its acceleration and heating close to the Sun. In contrast, the magnetic configuration of ICMEs is closed, and moreover
the momentum equation is dominated by magnetic forces. This implies no significant correlation between temperature and velocity,
as observed. 相似文献
9.
R.G. Gratton 《Astrophysics and Space Science》1999,265(1-4):157-164
Since about thirty years it is known that Oxygen and other α-elementsare overabundant in metal-poor stars. In this talk I
briefly review thehistorical and theoretical background, discuss reliability of presentabundance determinations for O, and
finally comment about the implicationsrelevant to galactic chemical evolution.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
10.
We present examples of umbral oscillations observed on Big Bear H filtergram movies and investigate the relation between umbral oscillations and running penumbral waves occurring in the same sunspot. Umbral oscillations near the center of the umbra are probably physically independent of the penumbral waves because the period of these umbral oscillations (150 s) is shorter than the penumbral wave period (270 s) but not a harmonic. We also report dark puffs which emerge from the edge of the umbra and move outward across the penumbra, and which have the same period as the running penumbral waves. We interpret these dark puffs to be the extension of chromospheric umbral oscillations at the edge of the umbra. It is suggested that the dark puffs and the running penumbral waves have a common source: photospheric oscillations just inside the umbra. 相似文献
11.
12.
We study the evolution of the longitudinal asymmetry in solar activity through the wave packet technique applied to the period
domain of 25 – 31 days (centered at the 27-day solar rotation period) for the sunspot number and geomagnetic aa index. We observe the occurrence of alternating smaller and larger amplitudes of the 11-year cycle, resulting in a 22-year
periodicity in the 27-day signal. The evolution of the 22-year cycle shows a change of regime around the year 1912 when the
22-year period disappears from the sunspot number series and appears in the aa index. Other changes, such as a change in the correlation between solar and geomagnetic activity, took place at the same
time. Splitting the 27-day frequency domain of aa index shows an 11-year cycle for higher frequencies and a pure22-year cycle for lower frequencies, which we attribute to
higher latitude coronal holes. This evidence is particularly clear after 1940, which is another benchmark in the evolution
of the aa index. We discuss briefly the mechanisms that could account for the observed features of the 22-year cycle evolution. 相似文献
13.
We compare the line profiles and frequencies of low =0, 1, 2 acoustic oscillations seen in observations in velocity (by the GOLF and GONG experiments) and in intensity (LOI instrument). Our study indicates that the systematic shift between the frequencies of low- pmodes in intensity and in velocity measurements recently discovered by Toutain and co-workers is merely an artifact of their reduction techniques. The results obtained agree perfectly with the theoretical expectation that solar oscillations are the global eigenmodes simultaneously visible in velocity and intensity with the frequencies and line profiles coinciding within the error bars. 相似文献
14.
Fitting observed power and cross spectra of medium-degree p modes in velocity (V) and intensity (I) has been widely used for getting information about the p-mode excitation process and, in particular, for trying to determine the type and location of the acoustic sources. Numerical simulations of solar convection allow one to “observe” velocity and temperature (T, used as proxy for I) fluctuations in different reference frames. Sampling the oscillations on planes of constant optical depth (τ-frame) closely corresponds to the observer’s point of view, whereas sampling the oscillations at constant geometrical height (z-frame) is more appropriate for comparison with predictions from theoretical models based on Eulerian hydrodynamics. The results of the analysis in the two frames show significant differences. Considering the effects introduced on oscillations by the steep temperature gradient of the photosphere and by the temperature- and pressure-dependent continuum opacity, we develop a new model for fitting the simulated V and T power and cross spectra both in the τ- and z-frames and discuss its merits and limitations. 相似文献
15.
Hα luminosities of a sample of galaxies in nearby compactgroups are presented. Our purpose is to study the influence of thegroup
environment on the star formation rates (SFRs) of the galaxies in thegroups, provided that the Hα luminosity is a good tracer of theSFR of disc galaxies. Measuring the global L
/L
B of the groups – including early-type galaxies – we find that the average value of the Hα emission is not significantly different from thatmeasured for field galaxies, and that most of the groups that show thehighest
level of L
/L
B, with respect to a set of synthetic groups built out of field galaxies, show tidal features in at least one of their members.
Finally, we have exploredthe relationship between the ratio L
/L
B and severalrelevant dynamical parameters of the groups (velocity dispersion, crossingtime, radius and mass-to-luminosity
ratio) and have found no clearcorrelation. This suggests that the exact dynamical state of a groupdoes not appear to control
the SFR of the group as a whole.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
16.
T. A. Polyakova 《Astrophysics》2003,46(1):18-23
Observations of the brightness and polarization of CEP over 1983-2002 are presented. An almost sinusoidal curve with a slightly varying amplitude and a period of about 850 days was fit to the light curve. The minima in the actual light curve often appear to be flooded with additional radiation compared to the smoothed curve. As an explanation of this phenomenon, we propose a working hypothesis whereby some radiation that is reflected back into the atmosphere near the equator through veiling by titanium oxide then partially diffuses into the near-polar regions where it escapes. 相似文献
17.
In the last four years we have carried out a number of studies on the radiative and collisional processes in theA
2
i
state of CN. Many of these of interest to those studying planetary atmospheres, comets and solar spectra are summarized in this paper. Data for CNA
2
i
fluorescence lifetimes and quenching rates, and collisional energy transfer between CNA
2
i
andX
2+ are reported. Detailed comparisons and a discussion of the results may be found in several already published papers. 相似文献
18.
Observations of two quiescent filaments show oscillatory variations in Doppler shift and central intensity of the He i 10830 Å line.The oscillatory periods range from about 5 to 15 min, with dominant periods of 5, 9, and 16 min. The 5-min period is also detected in the intensity variations, after correction for atmospheric effects. Doppler shifts precede intensity variations by about one period. The possibility that the oscillations are Alfvén waves is discussed.The Doppler signals of the filament form fibril-like structures. The fibrils are all inclined at an angle of about 25° to the long axis of the filament. The magnetic field has a similar orientation relative to the major direction of the filament, and the measured Doppler signals are apparently produced by motions along magnetic flux tubes threading the filament.The measured lifetimes of the small-scale fibrils of quiescent disk filaments are very likely a combined effect of intensity modulations and reshuffling of the structures. 相似文献
19.
Wolfram Kollatschny 《天文研究与技术》2003,(Z1)
1 IntroductionInmostcurrentworkingmodelsofAGNsacentralsupermassiveblackholeissurroundedbyabroademissionlineregion (BLR)atdistancesfrom 10 15toabout10 17cm .Thisregionisexpectedtobemoreorlesssphericalintheunifiedschemeofactivegalacticnuclei (AGN) .Thebroadlineregionissurroundedbyathickdustytorus.Inthesocallednarrowlineregion (NLR)thenarrowemissionlinesaregeneratedbyphotoionizationand/orshocks.Thisregionextendsfrom 10 17cmuptoseveralkpc .TheNLRisnotsphericallysymmetricinmostobservedcases… 相似文献
20.
Yu Xin Xiao-Bin Zhang Li-Cai DengNational Astronomical Observatories Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2002,2(6)
We present a snapshot of our recent results of a variable star survey in 1 degree fields around three open clusters: NGC 188, NGC 7789 and M67. A total number of 39 variable stars are newly discovered, including 22 W UMa stars, 10 EA (Algol) type binaries, one RR-lyr and one RRd pulsator, and five unclassified variables. 相似文献