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1.
The various physical parameters of a SNR can easily be worked out from graphs established on the basis of the recalibrated relation between the radio surface brightness , and the linear diameterD of a SNR (Ilovaisky and Lequeux, 1972). These graphs lead to the estimation of the distancer (kpc), linear diameterD (pc), monochromatic power at 1 GHz,P 1 GHz (W Hz–1); and total powerP tot (a) (erg. s–1) of a SNR, given its mean angular diameter <> (arc min), flux density at 1 GHz, S1 GHz (f.u.) and spectral indexa. Three SNR (W28A1, Monoceros SNR, W49B) are used to illustrate the case. The radio spectrum of one of these (W49B), curved at low frequencies, is explained in terms of absorption by the diffuse interstellar medium. Various cases are discussed and some physical parameters of the absorbing matter are established.  相似文献   

2.
To improve the scaling parameter controlling the impact crater formation in the strength regime, we conducted impact experiments on sintered snow targets with the dynamic strength continuously changed from 20 to 200 kPa, and the largest crater size formed on small icy satellites was considered by using the revised scaling parameter. Ice and snow projectiles were impacted on a snow surface with 36% porosity at an impact velocity from 31 m s−1 to 150 m s−1. The snow target was sintered at the temperature from −5 °C to −18 °C, and the snow dynamic strength was changed with the sintering duration at each temperature. We found that the mass ejected from the crater normalized by the projectile mass, πV, was related to the ratio of the dynamic strength to the impact pressure, , as follows: , where the impact pressure was indicated by P = ρtC0tvi/2 with the target density of ρt, when the impact velocity, vi, was much smaller than the bulk sound velocity C0t (typically 1.8 km s−1 in our targets). The ratio of the largest crater diameter to the diameter of the target body, dmax/D, was estimated by calculating the crater diameter at the impact condition for catastrophic disruption and then compared to the observed dmax/D of jovian and saturnian small satellites, in order to discuss the formation condition of these large dmax/D in the strength regime.  相似文献   

3.
Energetic particle (0.1 to 100 MeV protons) acceleration is studied by using high resolution interplanetary magnetic field and plasma measurements at 1 AU (HEOS-2) and at 5 AU (Pioneer 10). Energy changes of a particle population are followed by computing test particle trajectories and the energy changes through the particle interaction with the time varying magnetic field. The results show that considerable particle acceleration takes place throughout the interplanetary medium, both in the corotating interaction regions (CIR) (5 AU), and in quiet regions (1 AU). Although shocks may contribute to acceleration we suggest statistical acceleration within the CIRs is sufficient to explain most energetic particle observations (e.g., McDonaldet al., 1975; Barnes and Simpson, 1976).The first and second order statistical acceleration coefficients which include transit time damping and Alfvén resonance interactions, are found to be well represented byD T 8.5×10–6 T 0.5 MeV s–1 andD TT 4×10–6 T 1.5 MeV2 s–1 at 5 AU.By comparison, Fisk's estimates (1976), based on quasi-linear theory for transit-time damping, gaveD TT 5×10–7 T MeV2 s–1 at 1 AU.  相似文献   

4.
We have compared total solar irradiance from Nimbus-7 with ground-based photometry from the San Fernando Observatory (SFO) for 109 days between June 1 and December 31, 1988. We have also included in some analyses NOAA-9 SBUV2 data orF10.7 radio flux. The Nimbus-7 data are from orbital samples, averaged to the mean time of observation at SFO. Using the same parameters as in Chapmanet al. (1992), the multiple regression gives anR 2 = 0.9131 and a solar minimum irradiance,S 0, = 1371.76 ± 0.18 W m–2 for the best fit.  相似文献   

5.
Ultraviolet (200 nm) observations of 120 galaxies are performed in a 1.8 square degree field centered on the A 1367 cluster with a 40 cm imaging telescope flown on a stabilized balloon-borne gondola. Total ultraviolet fluxes are obtained and used to derive the current Star Formation Rate (SFR) in the cluster galaxies with measured Hi masses. A good correlation is found between the SFR per unit area and the gas surface density, similar to that previously found for a sample of field galaxies (Donaset al., 1987), while the mean gas depletion time-scale (M g/SFR) is probably shorter in the cluster than in the field.  相似文献   

6.
The standard classical expressions for the thermal synchrotron (TS) radiation from an optically thin thermal plasma are shown to be inapplicable at photon energiesEkT since they neglect quantum effects. Quantum relationships are obtained for the TS spectral emissivity, opacity, and polarization. The quantum TS spectra are much softer atEkT than the classical ones. The TS radiation exhibits strong linear polarization in the classical domain, whereas the quantum effects reduce the polarization at highE. Expressions for the classical TS luminosity are obtained with quantum corrections which turn out to be significant for (B/B c )(kT/mc 2)10–2(B c =4.41×1013 G).Fitting the gamma-ray burst (GRB) spectra by the classical TS law (see, e.g., Lianget al., 1983) is incorrect in cases wherekT is less than the maximum detected photon energy. The continua of the GRB spectra in the rangeE20 keV-2 MeV (Mazetset al., 1981a; Andreevet al., 1983) can be fitted satisfactorily by the quantum TS spectra. The results of this fitting may suggest the existence of temperatures much higher (up to 10 MeV), and of magnetic fields much lower (down to 109 G) than those usually accepted. Under these conditions the thickness of the TS sources (103–104 cm) could be comparable with their transverse dimensions (in contrast to sources with ordinary temperatures and fields), if they lie within a few kpc. The quantum TS spectra are too soft to account for the hard components (up to tens of MeV) of the GRB spectra detected by the Solar Maximum Mission (Nolanet al., 1984), unless the temperatures are unreasonably high.A straightforward TS interpretation of the GRB spectra seems to be unrealistic. Most probably, the continuum radiation escapes from an optically thick, strongly magnetized, highly non-stationary, hot plasma near the surface of a neutron star.  相似文献   

7.
The low l solar acoustic spectrum has been measured with great accuracy (v/v 10–4), for intermediate radial order modes, 11 n 34 (Jiménez et al., 1986; Grec, Fossat, and Pomerantz, 1983; Pallé et al., 1986). The measurement of the frequencies of modes of lower n, up to the fundamental one, are very important as they depart from asymptotic behaviour and, therefore, put more severe constraints on solar models. However, their amplitudes are very low (under 2 cm s–1) and when compared to the solar velocity background noise (Jiménez et al., 1986), a S/N 1 is obtained. Taking advantage of the fact that lifetimes seem to be higher at lower frequencies (lower n values) (Jefferies et al., 1988; Elsworth et al., 1990), very long Doppler velocity measurements, obtained at Teide Observatory, have been used to increase S/N, therefore, providing the possibility to detect such modes. The frequencies observed are compared to those predicted by a solar model (Christensen-Dalsgaard, Däppen, and Lebreton, 1988), using the best equation of state yet computed (Mihalas, Däppen, and Hummer, 1988).  相似文献   

8.
Macrospicules have been observed in H and He i D3, on the disk and above the limb. In 1975, a rate of 1400 (A day)–1 is inferred, and the ratio of equatorial to polar rates 2. D3 intensities are a few × 10–3 of the disk center, and do not decrease in coronal holes. The ratio of H to D3 intensities is 10. The integral number of macrospicules with D3 intensity I 0 is proportional to I 0 –1.  相似文献   

9.
On the basis of empirical (D)-dependency at the frequency of 5 GHz constructed using 15 planetary nebulae with the independently measured distances (10–171×10–20 W m–2 Hz–1 ster–1), we evaluated distances of 335 objects. Independent evidence of the correctness of the accepted scale are given. Then(D)-dependency is constructed and it is shown that atD<0.08 pc the mean electron density is higher than the one determined by the Seaton method. We showed that the filling factor diminishes with the increase of the PN diameter (1 atD0.08 pc and 0.2 atD0.4 pc). the ionized mass of 33 PNs is determined. With the diameter increase the ionized mass grows and atD0.4 pc reaches the valueM0.07M . We used the new distance scale when investigating the space distribution of PNs. The mean scale height =130±15 pc and the mean gradient of the change of surface densitym=0.37, which allowed us to estimate the total number of nebulae in the GalaxyN4×104. We divided the PNs according to their velocities (withV LSR>35 km s–1 andV LSR<35 km s–1) and permitted us to confirm that the PN belong to different sub-systems of the Galaxy. The estimated local formation rate of PNs [=(4.6±2.2)×10–12 pc–3 yr–1] is a little higher than the one of the white dwarfs. That can be explained by a large number of PNs having binary cores, which used in our sample. The statistical estimation of PN expansion velocity showed thatV ex increases from 5–7 km s–1 (atD0.03 pc) to 40–50 km s–1 (atD0.8 pc).  相似文献   

10.
Walraven, Walraven and Balona recently discovered several new periodicities in addition to the well-known fundamental and first overtone periods of the high-amplitude Scuti star AI Velorum. Linear nonadiabatic pulsation calculations were performed for an AI Velorum model of mass 1.96M , 24.05L , andT eff 7566 K for the radial and low-degree nonradial modes to help verify the tentative identifications made by Walraven, et al. Comparison of the calculated periods with the observations suggests some alternatives to the identifications proposed by Walraven, et al.  相似文献   

11.
The muon neutrino-antineutrino flux ratios, viz.,v /v generated from the decays of charged pions and kaons in atmosphere have been derived from the latest primary spectrum and the CERN ISRpp-collision data modified forp-nucleus interactions. The dynamical method of Allkoferet al. (1978) has been used in the present investigation. The estimated result forv /v yields 1.39 and 1.70 asE0 and , respectively. The neutrino fluxes from pion- and kaon-decay spectra have been calculated. Attention has been paid on prompt neutrino spectrum calculation from the decays ofD mesons. A rough estimate on the prompt muon spectrum has been given. The calculated results have been compared with the previous available results.  相似文献   

12.
Observations of the rms intensity fluctuations in the continuum obtained by Pravdjuk et al. (Solnechnye Dannye, No. 2, p. 70, 1974) from white-light photographs made with the Soviet Stratospheric Solar Observatory are analyzed to obtain a horizontal temperature-fluctuation amplitude as a function of depth. The results indicate that temperature fluctuations increase with depth monotonically from a small value at 50000.5 (cf. Figure 2). The initial rise of T appears quite steep, having a slope of approximately 20 K km–1. The model of Wilson (Solar Phys. 9, 303, 1969) is incompatible with the data. Convective flux in the present model is approximately 6% of the total flux at 5000 = 1.  相似文献   

13.
With the aid of the spectra taken in the years 1959–1968, a physical analysis of the atmosphere of P Cygni has been carried out and the motions of the atmosphere have been studied. The variations of radial velocities, the velocity progressions of Balmer and Hei lines, the high rate of mass loss (2×10–5 M yr–1), the features of the observed line profiles, especially that of H-K lines of Caii andD 1-D 2 lines of Nai confirm the conclusion of Van Blerkom (1978), concerning the assumption of an accelerating atmosphere for P Cygni. The electron density variation with the radius seems to ben e r –5/2, with an average value of 7×1011cm–3 at the lower boundary of the atmosphere.In order to explain the two absorption components of observed lines, an atmospheric model based on the assumption of three envelopes, two of which accelerate gradually with two different velocity laws (up to 11.2r c ), and the third of which accelerates rapidly with a standard velocity law (beyond 11.2r c ) has been developed. From this model and the observed profiles, the geometrical thicknesses of the line-forming regions of H, H, H, and H are derived.The observations were obtained at Haute Provence Observatory (CNRS).  相似文献   

14.
We use the polarimetric and intensity measurements of H and HeI D3 lines in solar prominences to derive the true geometrical thickness for several quiescent prominences. The electron densities, derived from the collisional depolarization in H by Bommier et al. (1994), are used to evaluate the thickness from the emission measure. The emission measure was obtained from the theoretical correlation with the H integrated intensity, according to Gouttebroze, Heinzel, and Vial (1993). Theoretical electron densities obtained by latter authors are also compared with those of Bommier et al. (1994) and we find a very good agreement between them. The prominence geometrical thickness exhibits a relatively large range of values from about 100 km up to a few 104 km. The plasma densities vary by almost two orders of magnitude in the observed structures, but the total column mass in the direction perpendicular to the prominence sheet seems to be fairly constant for the set of prominences studied.  相似文献   

15.
The crater populations of 18 lunar light plains (Cayley plains) show a variation in relative ages by a factor of about 4 in crater frequency of regions in the surroundings of the Orientale resp. Imbrium basin, and by a factor of greater than 25 for more distant sites. Thus the idea of a Moonwide synchronism in the emplacement of the lunar light plains with the formation of the basins Imbrium or Orientale cannot be supported.Some light plains are younger than the youngest basin Orientale. Since these plains cannot have been emplaced by any other basin-forming event and local impact-derived origin can certainly be excluded, an endogenic (magmatic) origin is proposed for these plains.Age determination data (D L -values) by Soderblom and Lebofsky (1972) and Soderblom and Boyce (1972) are shown to be correlated with own cumulative crater frequency data (N) for surfaces younger than 3.8 × 109 years; we findD L × N 0.6, different from the originally proposed relationD L × N. For ages > 3.8 × 109 years, theD L data by those authors, especially their light plains data, are incompatible with our crater frequency data.  相似文献   

16.
The paper deals with the excitation of the helium singlet level 21 P in the homogeneous and filamentary models of quiescent prominences with following parameters: the optical thickness at the limit of helium Lyman continuum 1c M = 0.1–100, T e = 7000 K, n e = 5 × 1010 cm–3. Assuming a model He atom with seven discrete levels (11 S, 23 S, 21 S, 23 P, 21 P, 33 D, 31 D) and the continuum the steady state equations for the levels 23 S, 21 P and the continuum have been solved together with the radiative transfer equations for the line 584 Å and the continuum 504 Å. The variations with depth of the functions n 2 3 S /n 1 1 S (1 c), n 2 1 P /n 1 1 S (1c ), and n + He n e /n 1 1 S(1c ) as well as the intensities of the triplet (D3, 10830 Å) and singlet (16678, 20581 Å) lines have been calculated. Comparison with observations leads to the following conclusions: (1) The line intensities calculated for filamentary models of prominences agree better with observations than those for homogeneous ones. (2) The helium level 21 P is excited by diffuse field 584 Å being formed by recombinations and spontaneous transitions 21 P – 11 S and escaping from the prominence into the space between the filaments and to the surface. (3) Underpopulation of the singlet level 21 P may be explained by combination of weak excitation mechanism (recombinations and formation of the diffuse field 584 Å) and strong deexcitation mechanism (spontaneous transitions into the level 11 S).  相似文献   

17.
As previously shown (Rabe, 1970), two classes of small periodic librations exist, in the plane, elliptic restricted problem, for an infinite sequence of easily specified oscillation frequenciesZ j . The present paper considers the dependence ofZ on the eccentricitye of the primary motion, in addition to its dependence on the mass parameter , and determines the resulting relations between ande, for any given periodic frequencyZ j . These relationships are obtained from the conditionD (Z j ,, e)=0, where the basic determinantD has been expanded up to terms of orderZ 20, 5, ande 4.Presented at the Conference on Celestial Mechanics, Oberwolfach, Germany, August 27–September 2, 1972.  相似文献   

18.
Solar H-flares now reported with their distinctive visual features have been statistically examined for a period of about eight years in relation to their different characteristics, flare-burst and flare-sunspot association. Important results obtained are: (i) Integrated intensity changes from the highest to the lowest values in the order F, H, E, and D flare type, whereas, impulsiveness in the order H, F, E, and D type, (ii) Flare-burst association is frequency dependent and is highest and lowest for H and D types respectively in almost all the frequencies, (iii) Most of the flares of D, E, and F types are associated with sunspots of p , p , and configurations having field strength 1500–2500 G, while that of H type with p and configurations having field strength 1000–2000 G.  相似文献   

19.
At present the wave theory of the spiral structure of the galaxies includes two alternative viewpoints. Two types of spiral waves—short-wave and long-wave modes—can be excited. According to Lin and Shu (1964) the short-wave modeK is responsible for the spiral structure of the galaxies and, according to Marochniket al. (1972), the long-wave mode (K 0). In our Galaxy theK -mode corresponds to the wave with an angular rotation velocity p =11–13 kms–1 kps–1 and a radial group velocity directed from the periphery to the center. TheK 0-mode corresponds to the wave having an angular rotation velocity p =23 ± 3 kms–1 kps–1 and a radial group velocity directed from the center of the Galaxy to its periphery. The theoretical and observational evidences in favour of Marochniket al.'s (1972) model are given.  相似文献   

20.
We report on eight X-ray bursts detected by ASTRON from the Rapid Burster (RB) on 13 and 28 April and 16 August, 1983. Six of them (trailing bursts), with durations of 1.5–2 min, rise times of 5–10 s and intervals of 1–1.5 hours, exhibit spectral softening during the burst decay and may be related to the type I bursts. Two of the bursts (triangle bursts) observed on 28 April at interval of 28 min with much longer rise times (30–50 s) and longer durations (3 min), do not show distinct spectral softening. Persistent flux from RB on 16 August was estimated asF p(2.0–2.4)×10–9 erg cm–2 s–1. Spectral evolution of two trailing bursts was investigated by fitting their spectra in consecutive time intervals with the blackbody (BB), isothermal scattering photosphere (SP) and thermal bremsstrahlung (TB) models. Around the burst maxima the SP model fits the data best whereas in the burst tails the TB model is generally better. The BB model is worse than at least one of the two others. Interpretation of the burst spectra in terms of the BB radiation leads to improbably small neutron star mass and radius (M<0.86M ,R NS<5 km) if the peak luminosity does not exceed the Eddington limit. Interpretation of the spectra around the burst maxima (3–15 s from the burst onset) in terms of an isothermal SP yields reasonable constraints onM,R NS, and distanceD. For instance, for the hydrogen photosphere we obtainedM=(1.0–2.1)M R NS=(7.1–16.4) km ifD=11 kpc. If one postulatesM=1.4M , thenD=(8.5–13) kpc for hydrogen photosphere; if, besides,D=11 kpc, thenR NS=(8.1–13.3) km. It follows also from the SP-interpretation that the photosphere radius may increase up to 20–30 km in maxima of the trailing bursts when the luminosity becomes close to the Eddington luminosity.  相似文献   

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