Statistical Tests of the Unification Scheme for High Luminosity Double Radio Sources

We have carried out some statistical tests of relativistic beaming and radio source orientation scenarios using the core dominance parameter Rand linear size D of a recent sample of double-lobed quasars and radio galaxies as orientation indicators. Our results show that the maximum Doppler boosting occurs within a cone angle of ∼ 13^°corresponding to an optimum Lorentz factor of ∼ 5. On the average, quasar cores appear to be boosted by a factor of ∼ 10 relative to those of radio galaxies. In general, we found that quasars lie at closer angles to the line of sight than radio galaxies with median values of 28^° and 51^°respectively, implying a relative foreshortening factor of ∼ 2. These results are consistent with the simple relativistic beaming and orientation-based unification hypotheses in which quasars are the beamed counterparts of powerful radio galaxies which form the isotropic parent population. The results show a strong evidence that orientation of source axis with respect to the line of sight is a crucial parameter in the classification schemes for radio sources. This revised version was published online in July 2006 with corrections to the Cover Date.     

活动星系核统一模式的统计检验

本文对视超光速源样本的有关数据进行统计分析，检验活动星系核统一模式。给出各类视超光速源的Ｒ（核光度与扩展区光度之比）分布和喷流与视线的平均夹角　。分析源样本的Ｒ、洛伦兹因子ｒ、喷流的投影尺度ｄ和线性尺度ｌ间的关系，发现Ｒ和ｄ之间存在反相关、ｒ和ｌ之间存在相关的特性，这些结果有利于说明活动星系核统一模式的取向效应。     

BL Lac天体和FR-I射电星系的统一模型(Ⅰ)

从射电结构的角度评述了BLLac天体和FR-I射电星系的统一模型的最新进展，内容包括射电结构、延展射电光度（Pext）、最大角尺度（LAS）、射电核主导系数（f）的比较以及对相对论聚束的测试。最新的射电观测资料表明XBLs是介于FR-I和RBLs之间的过渡型天体，这为BLLac天体是聚束的FR-I射电星系提供了一个很好的证据。     

Broad-Band Radio to X-Ray Properties of Seyfert Galaxies

We report on the statistical analysis of a sample of AGNs (Seyferts and LINERs) selected from an RBSC-NVSS sample of the brightest X-ray sources. The sample is large enough and unbiased for a detailed study of multi-frequency (radio to X-ray) properties of AGN. There are no significant differences in X-ray, optical, far-infrared, and radio powers, core dominance, radio loudness, radio spectral index, and two-point radio-to-optical and optical-to-X-ray spectral indices of Seyfert types 1 and 2. These findings strongly support the unification model, and the observed differences between Sy1 and Sy2 are due to both the variable obscuration and different geometric orientation effects. The correlation between the X-ray and radio emission over many decades is primary and indicates the intrinsically similar origin of both radiations in Seyfert galaxies, powered mainly by AGN, rather than compact starbursts. For Seyfert galaxies we found that the slopes of the relations L _X - L _R and L _X - L _B are flat, which indicate the existence of components unrelated with X-ray. Perhaps only for LINERs is the observed L _X - L _R relation completely due to AGNs. The Sy1, Sy2, and LINER galaxies show different slopes in the relation L _X - L _1.4, and the relative contribution of extended radio components may be the cause of these differences. The possible effects of unresolved extended radio and X-ray components are quantitatively discussed.     

Regions of He+ dominance in the high-latitude topside ionosphere

Observations of the occurrence of He⁺ dominance in the topside ionosphere are discussed. An earlier model of the behaviour of high-latitude H⁺ and O⁺ thermal plasma (Quegan et al., 1982) is extended to include He⁺ as a major ion. Calculations using the extended model show that plasma convection is likely to play a key rôle in producing regions of He⁺ dominance. Suggested conditions for He⁺ dominance are listed and their applicability to observed He⁺ behaviour is discussed.     

The Relationship between Radio Luminosity and Core-Dominance Parameter for XBLs

In this work, we investigate the correlation between the luminosity and the core-dominance parameter for a sample of X-ray selected BL Lacertae objects (XBLs), and found that the extended luminosity is strongly anti-correlated with the core-dominance parameter while the core (or the total) luminosity is not correlated with the core-dominance parameter. If this is the case, then we can expect that the lower extended luminosity XBLs and their core luminosity is relatively higher. This can be explained by a relativistic beaming model since in this case, the viewing angle is smaller and the emissions dominate the extended emissions. Therefore, the anti-correlation is in fact the result of the relativistic beaming model.     

High-redshift obscured quasars: radio emission at sub-kiloparsec scales

The radio properties of 11 obscured 'radio-intermediate' quasars at redshifts   z ≳ 2  have been investigated using the European Very-Long-Baseline-Interferometry Network (EVN) at 1.66 GHz. A sensitivity of  ∼25 μJy per 17 × 14 mas² beam  was achieved, and in seven out of 11 sources unresolved radio emission was securely detected. The detected radio emission of each source accounts for ∼30–100 per cent of the total source flux density. The physical extent of this emission is ≲150 pc, and the derived properties indicate that this emission originates from an active galactic nucleus (AGN). The missing flux density is difficult to account for by star formation alone, so radio components associated with jets of physical size ≳150 pc and ≲40 kpc are likely to be present in most of the sources. Amongst the observed sample steep, flat, gigahertz-peaked and compact-steep spectrum sources are all present. Hence, as well as extended and compact jets, examples of beamed jets are also inferred, suggesting that in these sources, the obscuration must be due to dust in the host galaxy, rather than the torus invoked by the unified schemes. Comparing the total to core (≲150 pc) radio luminosities of this sample with different types of AGN suggests that this sample of   z ≳ 2  radio-intermediate obscured quasars shows radio properties that are more similar to those of the high-radio-luminosity end of the low-redshift radio-quiet quasar population than those of Fanaroff–Riley type I (FR I) radio galaxies. This conclusion may reflect intrinsic differences, but could be strongly influenced by the increasing effect of inverse-Compton cooling of extended radio jets at high redshift.     

Ratio of the Core to the Extended Emissions in the Comoving Frame for Blazars

In a two-component jet model, the emissions are the sum of the core and extended emissions: \(S^{\mathrm{ob}}=S_{\mathrm{core}}^{\mathrm{ob}}+S_{\mathrm{ext}}^{\mathrm{ob}}\), with the core emissions, \(S_{\mathrm{core}}^{\mathrm{ob}}= f S_{\mathrm{ext}}^{\mathrm{ob}}\delta ^{q}\) being a function of the Doppler factor \(\delta \), the extended emission \(S_{\mathrm{ext}}^{\mathrm{ob}}\), the jet type dependent factor q, and the ratio of the core to the extended emissions in the comoving frame, f. The f is an unobservable but important parameter. Following our previous work, we collect 65 blazars with available Doppler factor \(\delta \), superluminal velocity \(\beta _{\mathrm{app}}\), and core-dominance parameter, R, and calculated the ratio, f, and performed statistical analyses. We found that the ratio, f, in BL Lacs is on average larger than that in FSRQs. We suggest that the difference of the ratio f between FSRQs and BL Lacs is one of the possible reasons that cause the difference of other observed properties between them. We also find some significant correlations between \(\log f\) and other parameters, including intrinsic (de-beamed) peak frequency, \(\log \nu _{\mathrm{p}}^{\mathrm{in}}\), intrinsic polarization, \(\log P^{\mathrm{in}}\), and core-dominance parameter, \(\log R\), for the whole sample. In addition, we show that the ratio, f, can be estimated by R.     

Instability by magnetic buoyancy

Recent developments in the theory of instability by magnetic buoyancy are discussed in an astrophysical context and, where appropriate, extended to provide a more unified picture. Emphasis is placed on the effects of density stratification and rotation, which are usually stabilizing. In one strongly-stratified and rapidly-rotating parameter régime, however, it is possible to render a magnetic field configuration unstable by increasing the statically-stable stratification, although increasing it beyond a certain limit eventually stabilizes the system, as one would intuitively expect.We find that stratification exerts a strongly stabilizing influence in the solar radiative interior, despite the high thermal diffusivity . Rotation plays a rather minor role. We emphasize the importance of a doubly-diffusive parameter D _* involving the ratio of to , the magnetic diffusivity, and find that magnetic buoyancy instability typically requires field strengths in excess of about 50 000 G. The development time ties in with the rise-time of buoyant flux tubes in a stably-stratified environment calculated by Parker (1974, 1975). A reasonable gradient of molecular weight in the central core could only stabilize a (mainly) toroidal field strong enough to affect the neutrino flux if the magnetic diffusivity were rather smaller than is usually supposed, for otherwise such a field would be subject to either a doubly-diffusive magnetic instability, which would initially take the form of overstable buoyancy oscillations, or rapid ohmic decay.In the solar convection zone we find that the rotation of the Sun has an extremely strong and suppressing influence on magnetic buoyancy instability, and that this is only likely to occur for large field strengths of about 1000 G in the top half of the zone.     

The interplay of mass loss and core overshooting in massive stars

In this study analytic models are used in an attempt to constrain the overshooting parameter in massive stars. It is found that core overshooting up to of order 20% is required to explain the non-existence of red supergiants withM _bol<–10. Furthermore, a critical mass of 60M marks the upper mass limit for stars that can undergo a red supergiant phase. The analysis employed clearly demonstrates an important interplay between mass loss and core overhooting-highlighting the difficulty of establishing the uniqueness of a given set of results.     

Relativistic beaming effects in the spectra of cores and hotspots in radio galaxies and quasars

We present the results of multiwavelength observations of cores and hotspots, at L , C , X and U bands with the Very Large Array, of a matched sample of radio galaxies and quasars selected from the Molonglo Reference Catalogue . We use these observations to determine the spectra of cores and hotspots, and test the unified scheme for radio galaxies and quasars. Radio cores have been detected at all wavelengths in all of the quasars in our sample, whereas only ∼50 per cent of the galaxies have cores detected in at least one of the wavelengths . The degree of core prominence in this sample is consistent with the unified scheme for radio galaxies and quasars. A comparison of the distributions of the two-point spectral index of the cores in our sample of lobe-dominated quasars, with the distributions in a matched sample of core-dominated quasars, shows that the distributions for these two classes are significantly different, and this is consistent with the expectations of the unified scheme. The difference in the spectral indices of the two hotspots on opposite sides is also significantly larger for quasars than for radio galaxies, as is expected in the unified scheme. We also investigate the relationship between the spectral index of the hotspots and the redshift or luminosity for our sample of sources.     

Stability valley for strange dwarfs

This is a study of the stability of strange dwarfs, superdense stars with a small self-confining core (M _core  < 0.02 M_⊙) containing strange quark matter and an extended crust consisting of atomic nuclei and degenerate electron gas. The mass and radius of these stars are of the same orders as those of ordinary white dwarfs. It is shown that any study of their stability must examine the dependence of the mass on two variables, which can, for convenience, be taken to be the rest mass (total baryon mass) of the quark core and the energy density ρ _tr of the crust at the surface of the quark core. The range of variation of these quantities over which strange dwarfs are stable is determined. This region is referred to as the stability valley for strange dwarfs. The mass and radius from theoretical models of strange dworfs are compared with observational data obtained through the HIPPARCOS program and the most probable candidate strange dwarfs are identified.     

Polarization of radio cores and the unified scheme

In the unified scheme for high-luminosity radio galaxies and quasars, the core-dominated quasars are seen at small angles to the line of sight and the lobe-dominated quasars at intermediate angles, while the radio galaxies lie close to the plane of the sky. In radio galaxies, the quasar nucleus is hidden from our view by a putative torus. Such a scenario should also affect the observed polarization properties of the cores, with the core-dominated quasars, lobe-dominated quasars and radio galaxies having progressively lower core polarization at a given frequency and higher rotation measure because of Faraday effects. In this paper, we report that the core polarization of weak-cored quasars has a median value of less than about 0.4 per cent and is indeed much smaller than for core-dominated quasars, where the median value is about 2.5 per cent. We suggest that this might be a result of the depolarization caused by the edge of the obscuring torus or disc. We also examine the relative orientation of the core-polarization E -vector at λ6 cm and the radio axis for the weak-cored quasars. The sample is small but does not show the significant trend reported earlier for cores of moderate strength. This could also be the result of Faraday rotation by the material in the edge of the torus or disc. These results are consistent with the basic ideas of the unified scheme.     

Constrained estimates of low-degree mode frequencies and the determination of the interior structure of the Sun

Low-degreep-modes penetrate to the solar centre and provide direct information about the core. However, the high observational accuracy that is required to resolve the details of the structure of the core is difficult to achieve because the oscillation power spectrum is significantly distorted by stochastic forcing of the oscillations, which appears as multiplicative noise. Here, an attempt is reported to reduce uncertainties of spectral parameter estimation by incorporating constraints imposed by smooth behaviour of some of the parameters (e.g., linewidths, background noise, rotational splitting) over a group of lines. Instead of estimating these parameters independently for each line, we determine them as smooth functions of frequency. It is expected that this procedure gives more accurate estimates of the average frequencies of any multiplet in the power spectrum, to which we have applied no constraints. We give some examples of the procedure for whole-disk measurements by the IPHIR space experiment. It is shown that the additional constraints do not result in significant changes in the frequency estimates, except for one mode whose peak in the power spectrum has the lowest signal-to-noise ratio. However, the uncertainty in the frequency of that mode does not influence substantially the results of the structure inversion in the core. Inversions of the IPHIR datasets are compared with corresponding inversions of data from the Birmingham Solar Oscillation Network (BISON). The IPHIR data indicate a sharp increase towards the centre of the deviation of the squared sound speed of the sun from that of a standard solar model, whereas the BISON data show a decrease. The difference between the IPHIR and BISON inversions is significant, preventing any definite conclusion about the deviation of the structure of the solar core from that of the model.     

Head-on collision of electron acoustic solitary waves in a plasma with nonextensive hot electrons

The head-on collision between two electron-acoustic solitary waves (EASWs) in an unmagnetized plasma is investigated, including a cold electrons fluid, hot electrons, obeying a nonextensive distribution and stationary ions. By using the extended Poincaré-Lighthill–Kuo (PLK) perturbation method, the analytical phase shifts following the head-on collision are derived. The effects of the ratio of the number density of hot electrons to the number density of cold electrons α, and the nonextensive parameter q on the phase shifts are studied. It is found that q and the hot-to-cold electron density ratio significantly modify the phase shifts.     

8.4 GHz VLA observations of the CfA seyfert sample

We present the results of an 8.4 GHz VLA survey of the CfA Seyferts. We find that the luminosity functions for Seyfert 1s and 2s are essentially identical, but that the type 2 objects are more likely to contain extended radio structures. This seems to be consistent with unified models for Seyferts, in which the differences between the two classes are largely due to orientation effects.     

A new pattern for the north–south asymmetry of sunspots

We study the solar cycle evolution during the last 8 solar cycles using a vectorial sunspot area called the LA (longitudinal asymmetry) parameter. This is a useful measure of solar activity in which the stochastic, longitudinally evenly distributed sunspot activity is reduced and which therefore emphasizes the more systematic, longitudinally asymmetric sunspot activity. Interesting differences are found between the LA parameter and the more conventional sunspot activity indices like the (scalar) sunspot area and the sunspot number. E.g., cycle 19 is not the highest cycle according to LA. We have calculated the separate LA parameters for the northern and southern hemisphere and found a systematic dipolar-type oscillation in the dominating hemisphere during high solar activity times which is reproduced from cycle to cycle. We have analyzed this oscillation during cycles 16–22 by a superposed epoch method using the date of magnetic reversal in the southern hemisphere as the zero epoch time. According to our analysis, the oscillation starts by an excess of the northern LA value in the ascending phase of the solar cycle which lasts for about 2.3 years. Soon after the maximum northern dominance, the southern hemisphere starts dominating, reaching its minimum some 1.2–1.7 years later. The period of southern dominance lasts for about 1.6 years and ends, on an average, slightly before the end of magnetic reversal.     

Towards a more habitable Mars — or — the coming martian spring

Two schemes are presented in which matter is moved closer to Mars so as to increase the equinoctal precession period of Mars. In such a way the Martian springs, during which Mars is habitable in the long winter model of Sagan (1971), could be extended and, in fact, prolonged indefinitely. The schemes involve using solar energy to move the satellite Phobos and/or material from the asteroid belt. Difficulties exist with the proposals but they are presented to stimulate discussion.