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1.
Using a multiple time-scale method, the weakly nonlinear waves on a self-gravitating incompressible fluid column are investigated. The analysis reveals that near the wavenumberk=k c , the amplitude modulation of a standing wave can be described by the nonlinear Schrödinger equation with the roles of time and space variables interchanged. The nonlinear cutoff wavenumber, which depends sensitively on initial conditions, can then be derived from the nonlinear Schrödinger equation so obtained. The finite amplitude standing wave is stable against modulation.  相似文献   

2.
The observed relation between the interstellar linear polarization curve parameters K and λ max characterizing the width and the wavelength of the polarization maximum, respectively, is interpreted quantitatively. We have considered 57 stars located in four dark clouds with evidence of star formation: in Taurus, Chamaeleon, around the stars ρ Oph and R CrA. In our modeling we have used the spheroidal dust grain model applied previously to simultaneously interpret the interstellar extinction and polarization curves in a wide wavelength range. The observed trend K ≈ 1.7λ max is shown to be most likely related to the growth of dust grains due to coagulation rather than accretion. The relationship of the interstellar polarization curve parameters K and λ max to the mean dust grain size is discussed.  相似文献   

3.
By integrating many charged particle trajectories in a magnetic field model consisting of a series of equally spaced field discontinuities with equal angular displacements, constant ¦B¦ and successive displacements oppositely directed, a parallel diffusion coefficient K ∥ is obtained. The particle gyroradius was kept sufficiently small for the interaction to be non-resonant. The diffusion coefficient is found to be in good agreement with that predicted by the known reflection properties for charged particles of individual discontinuities. However an attempt to reproduce the diffusion coefficient using the results of a recent study by Klimas and Sandri of a non-local diffusion equation applying to the non-resonant case lead to too low a value of K ∥. The computational approach was also applied to the case where the particle motion was in resonance with the wavelength of the train of discontinuities and a lower limit to K ∥ obtained. This lower limit exceeded the quasi-linear approximation value for K ∥ under resonant scattering conditions.  相似文献   

4.
We study the infrared (K s band) properties of clusters of galaxies in the Ursa Major supercluster using data from 2MASS (Two-Micron All-Sky Survey) and SDSS (Sloan Digital Sky Survey). We identified three large filaments with mean redshifts of z = 0.051, 0.060, and 0.071. All clusters of the supercluster are located in these filaments. We determined the total K s-band luminosities and masses for 11 clusters of galaxies within comparable physical regions (within a radius R 200 close to the virial radius) using a homogeneous method. We constructed a combined luminosity function for the supercluster in this region, which can be described by the Schechter function with the following parameters: M K * = ?24.50 and α = ?0.98. The infrared luminosities of the clusters of galaxies correlate with their masses; the M/L K ratios of the systems increase with their masses (luminosities), with most of the Ursa Major clusters of galaxies (particularly the richer ones) closely following the relations derived previously for a large sample of clusters and groups of galaxies. The total mass-to-infrared-luminosity ratio is 52 M ⊙/L ⊙ for six Abell clusters and 49M ⊙/L ⊙ for all of the clusters, except Anon2.  相似文献   

5.
Based on spectropolarimetric observations Seyfert 2 (Sy2) galaxies are generally divided into two populations. Some Sy2s show polarized broad emission lines (PBLs) which is an evidence for the hypothesis of the Unified model while others do not. In order to determine the properties of these two apparently different populations we compiled a sample of 66 Sy2 objects with and without detected PBLs. We used a (J − H) − (H − Ks) diagram based on 2MASS J, H, Ks magnitudes in 14 arcsec aperture, the F[OIII] emission line flux and the infrared emission flux FKs using the Ks filter. From the (J − H) − (H − Ks) diagram we determined that one third of the Sy2 objects with PBLs have a power-law infrared component which could be a result of both a non-thermal AGN component scattered by free electrons (or dust) and emission from hot dust near its sublimation temperature. The rest of the objects (with PBLs) are significantly dominated by a dust thermal re-emission. The Sy2s without PBLs show infrared emission dominated by a host galaxy stellar component and also by thermal dust re-emission. The Sy2s with PBLs tend to have a few times larger L[OIII] luminosities than those without. Following the median values of F[OIII]/FKs, it seems that this ratio is sensitive enough to separate our sample of Sy2 galaxies into two types - with and without PBLs. There are no Sy2s with PBLs having Eddington ratio below 10−3 which confirms the results of Nicastro et al. (2003).  相似文献   

6.
Based on data from the Two-Micrometer All-Sky Survey (2MASS), we analyzed the infrared properties of 451 Local-Volume galaxies at distances D ≤ 10 Mpc. We determined the K-band luminosity function of the galaxies in the range of absolute magnitudes from ?25m to ?11m. The local luminosity density within 8 Mpc is 6.8 × 108L⊙ Mpc?3, a factor of 1.5 ± 0.1 higher than the global mean K-band luminosity density. We determined the ratios of the virial mass to the K-band luminosity for nearby groups and clusters of galaxies. In the luminosity range from 5 × 1010 to 2 × 1013L⊙, the dependence log(M/LK) ∝ (0.27 ± 0.03) log LK with a dispersion of ～0.1 comparable to the measurement errors of the masses and luminosities of the systems of galaxies holds for the groups and clusters of galaxies. The ensemble-averaged ratio, 〈M/LK〉 ? (20–25) M⊙/L⊙, was found to be much smaller than the expected global ratio, (80–90)M⊙/L⊙, in the standard model with Ωm = 0.27. This discrepancy can be eliminated if the bulk of the dark matter in the Universe is not associated with galaxies and their systems.  相似文献   

7.
We present our JHKLM photometry for R Cas performed during 1988–2000. The pulsation period of R Cas is $P \approx 429\mathop .\limits^d 6$ , with the maximum IR brightness lagging behind the maximum visual brightness by ～0.2 P. The amplitude of light variations appreciably decreases with increasing wavelength at λ≤3 μm. At λ>3 μm, this decrease virtually ceases. There is a step on the ascending branch of IR JHK brightness. The K-L color index increases linearly with K magnitude: $K - L = 0.304K + 1\mathop .\limits^m 20$ . The color temperature dependence, T K-L =f(K), is also linear: T K?L = ?622K + 1100 K. In going from minimum to maximum, the K flux (as well as the bolometric flux) from the star and its color temperature T K-L increase by a factor of ～2.2 and ～1.3, respectively.  相似文献   

8.
Computerized spherical harmonic analysis is applied to the morphology of the southern auroral oval. Records from 23 All Sky Camera stations together with visual observation reports for the period 1957–1959 constitute the raw data set. The mode of the derived auroral occurrence distribution function F(Kp, θ, φ) is regarded as the maximum probability contour and yields a set of auroral ovals. These 10 contours, one for each Kp level, are expressed in the invariant magnetic co-ordinates of Bond (1968).  相似文献   

9.
Geomagnetic pulsations, in the period range 10–150 sec, have been analysed from five stations; Eskdalemuir (L = 3.1), Lerwick (L = 4.0), St. Anthony (L = 4.9), Sodankyla (L = 5.3) and Tromsø (L = 6.6). The results of 12 observatory years' worth of data are presented in the form of contour maps showing the frequency of occurrence of the pulsations as a function of Kp index and of local time. The maps show that a ground based observatory is more likely to record shorter period oscillations (pc 3) when the geomagnetic field line linking the station with the southern hemisphere passes through the plasmatrough than when the observatory field line links the plasmasphere. The peak occurrence of pc 3 for the observatories considered is at 08:45 hr ± 1 hr LT and is related to the observatory L value and the average night-time Kp index by the equation, L = 8.1 ? 1.2Kp. At Eskdalemuir, the spectrum is broader band than the other stations and tends to divide into two peaks; the pc 3 (20 sec) peak tends to occur when the plasmapause has moved in close to the observatory; while the pc 4 (60 sec) peak occurs when the Kp values have been lower and the plasmapause is further away at higher latitudes.  相似文献   

10.
《Planetary and Space Science》2007,55(10):1218-1224
In this paper, we report the results derived from a statistical analysis of whistlers recorded at Varanasi during the period January 1990–December 1999. The monthly occurrence rate shows a maximum during January to March. In order to study the role of geomagnetic disturbance on the whistler occurrence rate, we have used the KP index and its variation. It is found that the occurrence probability monotonically increases with ∑KP (daily sum) values. It is found that, when ∑KP>20, the occurrence rate is greater than the average value, in good agreement with results reported by other workers. In addition, we also present the probability of the observation of whistlers during weak/intense geomagnetic storms and also during the main phase and recovery phase of geomagnetic storms.  相似文献   

11.
A V-band nova search was carried out in NGC 3627 with archival Hubble Space Telescope WFPC2 data which was obtained in the period between November 1997 and January 1998. A total of four novae candidates were discovered which corresponds to a global nova rate of R = 83.65 ± 7.58 yr−1. Taking into account the K-band luminosity obtained from 2MASS (Jarrett et al., 2003) yielded a luminosity specific nova rate (LSNR) of νK = 9.60 ± 1.64 novae per year per 1010L⊙,K. Excluding one of the candidates which may be a long-period variable leads to a LSNR of νK = 7.20 ± 1.23 novae per year per 1010L⊙,K. These values are higher than other known nova rates for external galaxies except the Magellanic Clouds.  相似文献   

12.
It has been recently observed by XMM-Newton that besides the emission line of iron Kα at 6.4 keV there also exists in the Seyfert 1 galaxy NGC 3783 the very intense emission line of iron Kβ at 7.0 keV. Moreover, the ratio of equivalent widths (EWs) of these two lines can hardly be interpreted with the traditional mechanism of “photoelectric absorption — fluorescence emission”. By using the mechanism of Cerenkov line-like radiation proposed by YOU Jun-hian et al., the ratio of EWKα/EWKβ may be reasonably interpreted by means of a detailed model theoretical computation. As shown by the results, the iron K lines in active galactic nuclei (AGNs) are formed not only by the fluorescence mechanism, but also by the Cerenkov line-like radiation. Both coexist in AGNs, with the latter playing the dominant role.  相似文献   

13.
Crank-Nicholson solutions are obtained to the time-dependent Fokker-Planck equation for propagation in the interplanetary medium following a point in time injection of energetic solar particles and including the acceleration terms $$\frac{\partial }{{\partial T}}\left( {D_{TT} \frac{{\partial U}}{{\partial T}}} \right) - \frac{\partial }{{\partial T}}\left( {\frac{{D_{TT} U}}{{2T}}} \right)$$ . The diffusion coefficient in kinetic energyD TT is allowed to be either independent of radial distance,R(AU), or follow the lawD TT=D0T2R 0 2 /(A2+R2) in either case with the 1 AU value ofD TT at 10 MeV ranging between 10?4 (MeV)2 s?1 and zero. The spatial diffusion mean free path at the Earth's orbit is fixed at λ‖ AU at 10 MeV according to numerical estimates made by Moussas and Quenby. However, a variety ofR dependences are allowed. Reasonable agreement with experimental data out to 4 AU is obtained with the above values ofD TT and the spatial diffusion coefficientK r=K0R?2 forR«1 andK r=K0R0.4 forR»1 AU. It is only in the decay phases of prompt events as seen at 2–4 AU that significant differences in the temporal behaviour of the events can be distinguished, depending on the value ofD TT chosen within the above range. Experimental determination of the decay constant is difficult.  相似文献   

14.
Recent observations of partial penetration of the IMF By into the magnetosphere (Fairfield, 1979; Cowley and Hughes, 1983) are shown to agree with the idea of a magnetopause current Ky, induced by IMF By (Primdahl and Spangslev, 1983). The slow decay of Ky, caused by Joule heat losses in the cusp ionospheres is responsible for the appearance (on the average) of a fraction of IMF By inside the magnetosphere, and this also explains the large statistical scatter of the data. A decay time constant of 4–5 days is derived from the average fraction of IMF By observed inside the magnetosphere in good agreement with the 7-day time constant previously proposed.  相似文献   

15.
One year of magnetic field data from the geostationary spacecraft ATS 6 have been analysed for effects associated with the equatorial plane components of the interplanetary magnetic field (IMF). It is shown that perturbation fields in the Y (dawn to dusk) direction appear in association with the Y component of the IMF, in agreement with previous theoretical suggestions. On average a fraction 0.28 ± 0.02 of the IMF Y field appears at geostationary orbit, such that the average ATS 6 By field is 1.9 ± 0.4 nT larger when IMF By is positive than when it is negative. The perturbation field magnitudes are also found to depend strongly on local time, however, with largest effects appearing in the midnight and dawn quadrants, where the average perturbation fields are nearly half the simultaneous IMF Bv. field. At noon this fraction drops to one fifth, and no average effect occurs in the dusk quadrant. Both the daily mean perturbation fields and the diurnal modulation are also found to depend upon the level of magnetic disturbance as measured by KP, or equivalently upon IMF Bz, and upon season of the year. Overall stronger daily mean perturbation fields occur when KP is low or when IMF Bz is positive, than when KP is high or when IMF Bz is negative. This effect is not linear, however, and there is also a trend in the data towards increasing perturbation fields with IMF Bz negative and decreasing. On dividing the data according to season, increasingly strong daily mean effects are found in the order winter, summer and equinox for both quiet and disturbed magnetospheres. Diurnal modulations of the perturbation field magnitudes for low KP (IMF Bz > 0) take the form of large amplitude quasi-sinusoidal variations about mean values which are very marked in the equinox data, are present to a lesser degree during summer and are absent during winter conditions. When Kp is high (IMF Bz < 0) significant deviations from mean perturbation field values occur generally only during nightside hours and little seasonal dependence is evident. Finally, it is shown that the highest correlation between the IMF data and the ATS 6 perturbation fields occurs with zero time delay between the two data sets, showing that a prompt response to IMF conditions occurs at geostationary orbit within the 1 h time resolution available in this study. Although many details of the above ATS 6 response remain to be understood, these results overall demonstrate in a very direct manner the magnetically “open” nature of the Earth's magnetosphere.  相似文献   

16.
A continuous 300-day, world-wide laser-ranging data of the satellite STARLETTE between October 1976 and July 1977 was used to analyse the perturbation of the orbit by ocean tide. The long-period (longer than 20d) perturbations in the orbital inclination by the four main tide components K1, P1, K2, S2 were clearly identifiable in the maximum entropy power spectrum and periodogram. By comparing orbits including and excluding the tidal terms, the effect of the tide on the position of the satellite over 5 days was found to be of the order of one meter.  相似文献   

17.
We report the results of the first-ever CCD spectroscopic observations of the eclipsing variable CCCas with massive early-type components. The measured semi-amplitudes of the radial velocity curves of the components, K 1 = 123.9 km/s and K 2 = 292.4 km/s, are comparable with the published data, and the center-of-mass velocity of the system was found to be V 0 = ?20.4 km/s, which is about ?10 km/s greater than the earlier published results. This fact may support the published hypothesis about the presence of a third body in the system.  相似文献   

18.
Based on the analysis of published data on exposure ages of iron meteorites determined with the 40K/K method (T K) and ages calculated using short-lived cosmogenic radionuclides (with the half-life T 1/2 < 1 Myr) in combination with stable cosmogenic isotopes of noble gases (TRS), the following results have been obtained. (1) The distribution of T RS ages (106 values) has an exponential shape, similar to that for ordinary chondrites, but different from the distribution of T K ages (80 values). The difference is most likely due to small amounts of data for meteorites with low T K ages (less than ~200–300 Myr). The latter can be ascribed to the difficulty of measurement of small concentrations of cosmogenic potassium isotopes. This circumstance makes the selection of meteorites with 40K/K ages nonrepresentative and casts doubt on the correctness of conclusions about the variations of the intensity of galactic cosmic rays (GCR) based on the analysis of distribution of these ages. (2) The magnitude of the known effect (systematic overestimation of T K ages in comparison with T RS ages) has been refined. The value k = T K/T RS = 1.51 ± 0.03 is acquired for the whole population of data. We have shown the inefficiency of the explanation of this effect on account of an exponential change in the GCR intensity (I T ) with time (T) according to the relation I T = I 0exp(–γT) over the whole range of ages of iron meteorites. (3) In order to explain the overestimation of T K ages in comparison with T RS ages, a model has been proposed, according to which the GCR intensity has exponentially increased in the interval of 0–1500 Myr governed by the relation: I T = I T = 1500 (1 + αexp(–βT)). For one of the variants of this model, the GCR intensity has exponentially increased by a factor of two only over the recent ~300 Myr, remaining approximately constant for the rest of the time. The data acquired with the use of this model indicate that the measured T K ages are close to the actual time that the meteorites existed in space; the data are in agreement with the observed exponential distribution of T RS ages.  相似文献   

19.
We have studied the dayside magnetosphere structure and its Kp, AE and IMF-dependence using the magnetic data from IMP and HEOS satellites obtained during 1966–1972. An analysis of the field line configurations has been done on the basis of results of a least squares fitting of the model coefficients to the data subsets. The plots of the magnetopause subsolar point distance and of the polar cusp latitude vs Kp and AE have been obtained. A detailed study of the model field distribution has revealed a substantial difference in the polar cusp field line geometry between the cases of weak and strong geomagnetic activity. We find that this results in a considerable longitudinal extension of the isointensity contours of particle precipitation at ionospheric heights during disturbed periods with Kp ? 3 or AE ? 300 nT. The same effect has been detected for the data subsets corresponding to the IMF Bz < 0. In contrast, at quiet times the precipitation isolines are much closer to circles. We conclude therefore that the cleft-like structure of polar cusps pertains only to active periods and can be explained by a magnetic effect of enhanced Birkeland currents.  相似文献   

20.
Assuming that the formation of the ring current belt is a direct consequence of an enhanced crosstail electric field and hence of an enhanced convection, we calculate the total ring current kinetic energy (KR) and the ring current energy injection rate (UR) as a function of the cross-tail electric field (ECT); the cross-tail electric field is assumed to have a step function-like increase. The loss of ring current particles due to recombination and charge-exchange is assumed to be distributed over the whole ring current region. It is found that: (1) the steady-state ring current energy KR is approximately linearly proportional to ECT; (2) the characteristic time tc for KR to reach the saturation level is 3–4 h; (3) the injection rate UR is proportional to ECTβ where β ? 1.33?1.52; and (4) the characteristic time tp for UR to reach the peak value is 1–2 h and the peak UR value is 50% higher than the steady-state value. Since β is now determined specifically for an enhanced convection, an observational determination of the relationship between ECT(or φCT) and UR is essential to a better understanding of ring current formation processes. If the observed β is greater than 1.5, additional processes (e.g. an injection of heavy ions from the ionosphere to the plasma sheet and subsequently to the ring current region) may be required.  相似文献   

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