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1.
The very early universe must have been extremely homogeneous, even on scales far exceeding the particle horizon. Within the framework of the standard Friedmann cosmology, homogenization can only be achieved by quantum effects which violate classical causality. This could happen when the particle horizon was smaller than the Compton wavelength of the pion. The assumption that statistical departures from equilibrium started to grow after this epoch leads to a prediction of the density fluctuations at recombination. The amplitude ν of the fluctuations should have a maximum of about 0.007 on scales of 81017M. For smaller scales, ν ∝M +1/6, and for larger scales, ν ∝M ?1/2. This suggests that superclusters condense out at a red shift of about 11, and clusters and then galaxies form shortly after by fragmentation.  相似文献   

2.
The velocity field of main-sequence stars and red giants from the TGAS catalogue with heliocentric distances up to 1.5 kpc has been analyzed for various spectral types. To estimate the influence of a low accuracy of stellar parallax measurements on the results of a kinematic analysis of distant stars, first we have studied in detail how the kinematic parameters derived with 1/π distances are shifted when these distances are replaced by three other versions of distances from Astraatmadja et al. (2016b). We have obtained detailed tables in which the ranges of these shifts in the Ogorodnikov–Milne and Bottlinger model parameters are shown for the stars of each spectral type. We have the smallest shifts in the case of determining the Oort coefficients A and B, for which there are 10% shifts only for main-sequence stars of spectral type B. In the remaining cases, these shifts are 0–3%. For the remaining parameters the shifts do not exceed 30%. Thus, we have shown that using the 1/π distance scale in estimating the Ogorodnikov–Milne and Bottlingermodel parameters (except for the parameter Ω″0) yields reliable results even when using parallaxes with large relative errors (up to 60%). To study Parenago’s discontinuity, we have investigated the dependence of the Ogorodnikov–Milne and Bottlinger model parameters on color for 1 260 071 mainsequence stars and 534 387 red giants. As far as we know, such a data set is used for the first time to investigate Parenago’s discontinuity. The main result is the detection of maximum points at B ? V = 0.75 after which the solar velocity component V and the Oort coefficient B decrease when moving from blue stars to red ones. This fact is a new feature of Parenago’s discontinuity, because the component V does not change in the classical case at B ? V >0.6. We have made an attempt to represent the well-known Parenago’s discontinuity as a special case of the more complex effect of a gradual change in a number of kinematic parameters as the mean age and composition of the group of stars under study changes.  相似文献   

3.
A new period (P=2 . d 9042997) of the eclipsing binary system VZ Hydrae has been given, which is based on all the available times of minima. The period based on the photoelectric epochs has also been presented. The O?C diagram and detailed period study of VZ Hya have been presented for the first time, and the period changes have been estimated in different portions of the O?C diagram. Significant period changes do not appear to have occurred in VZ Hya, however, the O?C diagram suggests that the period of the system shows a slow tendency to increase. Period changes of 10?5 d (?) to 10?7 d have occurred around the years 1933, 1971, and 1975. All four period changes are noted in the time-interval 1918 to 1978. Upward treands appear stronger than the declining trends. Secondary minima show larger fluctuations than the primary minima. The fluctuations of the O?C values around the zero-line of VZ Hya demands notice for searching out the cause of period variations such as the presence of a third body.  相似文献   

4.
Analyses based on irradiance observations from space within the last one and a half decades have discovered variations in the entire solar spectrum and at UV wavelengths on time scales of minutes to decades. In this paper we analyze the distribution of the measuring uncertainties and daily fluctuations in total solar irradiance measured by the Nimbus-7/ERB and SMM/ACRIM I radiometers as a function of solar cycle. Changes in solar total irradiance and its surrogates shorter than the solar rotation have also been considered as noise and have been removed from the data. Our results show that the noise (both instrumental and solar noise) changes as a function of the solar cycle, being higher during high solar activity conditions. The analysis of the scatter plot diagrams between the data and their standard deviation, the so-called dispersion diagrams, provides a useful tool to estimate and predict the time of solar maximum and minimum activity conditions.Deceased on October 13, 1994.  相似文献   

5.
Jakimiec  Maria  Antalová  Anna  Storini  Marisa 《Solar physics》1999,189(2):373-386
The relationship between the galactic cosmic ray modulation (CR) and the non-flare coronal level, as given by the solar soft X-ray background (XBG), is investigated from 1 July 1968 to 30 June 1980 on a daily basis. The stationarity problem of a multivariate time series, as well as the role of the short- and medium-term corona variability are faced. From them it is found that the CR/XBG relation is variable during the considered heliomagnetic semicycle, while CR and XBG are highly anticorrelated on a long-time scale (12-month averages). The CR/XBG relationship during the declining phase of solar activity shows a moderately strong anticorrelation, on short- and medium-term time scales (coefficient up to –0.77 for 27-day running averages), went towards insignificant values in the minimum phase and is only partially reconstructed during the rise of the following solar cycle. During the solar activity maximum of cycle 20 the cosmic-ray modulation is only related to the short-term coronal fluctuations (no other time scales are significant, supporting the reliability of the so-called `Gnevyshev gap' in solar parameters).  相似文献   

6.
A study of the Earth’s rotation in space reveals a complex pattern of variations in its orientation, the excitation mechanisms of these variations, and their manifestations in various natural processes. The Earth’s rotation rate is not constant but exhibits complex fluctuations that account for some fraction of 108 (corresponding to variations of several milliseconds (ms) in the length of the day). These variations span a wide spectrum of time scales, from hours to centuries or longer, reflecting the fact that they are produced by a wide variety of geophysical and astronomical processes. We discuss the results of our statistical comparison of long series of observations to reveal the most coherent variations. The spectral composition of the experimental time series has been determined using modified periodogram and single-channel autoregression methods. A comparative analysis has been performed by a two-channel autoregression spectral estimation method. The results of our comparison of the time series suggest that the fluctuations with periods of about 73 years are highly coherent.  相似文献   

7.
The motions of the components of wide binary stars in the regular Galactic gravitational field on time scales ~1010 yr at various Galactocentric distances R 0 have been studied numerically. Near the Galactic center, the influence of the bar has been taken into account. The regions of restricted motions of the components in wide pairs have been found depending on the initial conditions: the magnitude of the relative velocity of the components, their mutual distance, and the inclination of the relative velocity vector to the Galactic plane. The shape and sizes of these regions are shown to depend significantly on R 0: the sizes of the region of initial conditions corresponding to restricted motions increase with R 0. Profound changes in the eccentricity of the binary orbit occur at inclinations close to 90?, which can lead to close approaches of the stars with a pericenter distance less than 1 AU. For retrograde motions (the binary rotates in a direction opposite to the Galactic rotation), there are elongated branches of the region of restricted motions in all cases, which extend at least to 10 pc in some cases.  相似文献   

8.
Molkov  S. V.  Lutovinov  A. A.  Falanga  M. 《Astronomy Letters》2015,41(10):562-574

We have investigated the temporal variability of the X-ray flux measured from the high-mass X-ray binary LMCX-4 on time scales from several tens of days to tens of years, i.e., exceeding considerably the orbital period (~1.408 days). In particular, we have investigated the 30-day cycle of modulation of the X-ray emission from the source (superorbital or precessional variability) and refined the orbital period and its first derivative. We show that the precession period in the time interval 1991–2015 is near its equilibrium value P sup = 30.370 days, while the observed historical changes in the phase of this variability can be interpreted in terms of the “red noise” model. We have obtained an analytical law from which the precession phase can be determined to within 5% in the entire time interval under consideration. Using archival data from several astrophysical observatories, we have found 43 X-ray eclipses in LMC X-4 that, together with the nine eclipses mentioned previously in the literature, have allowed the parameters of the model describing the evolution of the orbital period to be determined. As a result, the rate of change in the orbital period ? orb/P orb = (1.21 ± 0.07) × 10?6 yr?1 has been shown to be higher than has been expected previously.

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9.
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10.
The algorithm ztrace of Monaco & Efstathiou is applied to the IRAS PSCz catalogue to reconstruct the initial conditions of our local Universe with a resolution down to ~5  h 1 Mpc. The one-point probability distribution function (PDF) of the reconstructed initial conditions is consistent with the assumptions that: (i) IRAS galaxies trace mass on scales of ~5  h 1 Mpc and (ii) the statistics of the primordial density fluctuations are Gaussian. We use simulated PSCz catalogues, constructed from N -body simulations with Gaussian initial conditions, to show that local non-linear bias can cause the recovered initial PDF (assuming no bias) to be non-Gaussian. However, for plausible bias models, the distortions of the recovered PDF would be difficult to detect using the volume finely sampled by the PSCz catalogue. So, for Gaussian initial conditions, a range of bias models remain compatible with our PSCz reconstruction results.  相似文献   

11.
Analytic treatments of a particle encountering a collisionless shock have commonly been based on the assumption that the shock surface is quasi-planar with length scales larger than the particle gyroradius. Within this framework, the particle distribution function width is supposed to be conserved in any shock reflection process. It is well known, however, that the thermal energy associated with backstreaming ions upstream of Earth's bow shock is significantly larger than the incident solar wind thermal energy. In a previous study, we found that non-thermal features of ions reflected quasi-adiabatically can be accounted for by considering the effect of small, normally distributed fluctuations of the shock normal over short temporal or spatial scales. The strong dependence of the particle acceleration on shock geometry leads to an increase in the temperature and to a non-thermal tail. Here, we conduct a similar analysis to investigate the effects of small, normally distributed fluctuations in the shock normal direction for specularly reflected ions. This later mechanism is considered of first importance in the dissipation process occurring at quasi-perpendicular shocks. We have derived the probability distribution functions f(v∥) and f(v⊥) of ions issued from a specular reflection of incident solar wind in the presence of normal direction fluctuations. These distributions deviate weakly from a Maxwellian, in agreement with the observations. In particular, a qualitative agreement with the ion thermal energy is obtained for fluctuations of the normal orientation in the 5-8° range about the nominal direction. Also, we have found that the shock θBn has a weak effect on the shape of the distribution. While, not a strong determinant of the reflected distribution characteristics, the dynamical shock structure at ion scales cannot be ignored when accounting for the shock-accelerated particle thermal energy.  相似文献   

12.
This paper presents a correlative study between the peak values of geomagnetic activity indices (Dst, Kp, ap and AE) and the peak values of various interplanetary field (Bt, Bz, E and σB) and plasma (T, D, V, P and β) parameters along with their various products (BV, BzV and B2V) during intense geomagnetic storms (GMSs) for rising, maximum and decay phases as well as for complete solar cycle 23. The study leads to the conclusion that the peak values of different geomagnetic activity indices are in good correlation with Bt, Bz, σB, V, E, BV, BzV and B2V, therefore these parameters are most useful for predicting GMSs and substorms. These parameters are also reliable indicators of the strength of GMSs. We have also presented the lag/lead time analysis between the maximum of Dst and peak values of geomagnetic activity indices, various interplanetary field/plasma parameters for all GMSs. We have found that the average of peak values of geomagnetic activity indices and various field/plasma parameters are larger in decay phase compare to rising and maximum phases of cycle 23. Our analyses show that average values of lag/lead time lie in the ≈?4.00 h interval for Kp, ap and AE indices as well as for Bt, Bz, σB, E, D and P. For a more meaningful analysis we have also presented the above study for two different groups G1 (CME-driven GMSs) and G2 (CIR-driven GMSs) separately. Correlation coefficients between various interplanetary field/plasma parameters, their various products and geomagnetic activity indices for G1 and G2 groups show different nature. Three GMSs and associated solar sources observed during three different phases of this solar cycle have also been studied and it is found that GMSs are associated with large flares, halo CMEs and their active regions are close to the solar equator.  相似文献   

13.
The paper deals with massive fluid spheres with an isothermal core (having finite central density) and a polytropic envelope in terms of the General Relativity. The matching of the solutions in the core and envelope has been done using Bondi's condition,H=0 and also without it. The study reveals that since this condition does not correspond to any particular physical situation the maximum values of fractional core size, fractional core mass and the redshift do not occur atH=0, but that they occur at some other point. Within the permissible physical conditions (dP/dρ≤1) the maximum values ofM core/M,R core/R and the surface redshift, for an isothermal coreP=ρ/3, are respectively 0.473, 0.554, and 0.565. Using the conditionH=0, it has been shown that for isothermal cores corresponding to the equation of the stateP≥0.6ρ, the configurations are pulsationally unstable.  相似文献   

14.
The development of three intense active centers during their appearance on the solar disk is examined using high resolution observations at 2.8 cm. Each region shows a very bright component with brightness temperature > 106 K and size smaller than 20.The development of the bright components have been investigated on different time scales. Intensity fluctuations on a time scale of minutes are within the instrumental accuracy while the evolution over periods of days shows a variation of the flux density up to 30–40% per day.The problem of the bright cores height is discussed. Heights within 10 × 103 and 40 × 103 km are found using their apparent displacement on the disk.  相似文献   

15.
The paper presents experimental evidence for the existence of fast intensity fluctuations with time scales of the order of a minute in the X-ray emission from Cyg X-1 at energies greater than 29 keV. Spectral variations over time intervals of 20–25 min are also observed in the same energy range. Whereas, similar intensity and spectral fluctuations have been reported earlier at lower energies the observations presented here is the first evidence for the existence of similar fluctuations at high energies.  相似文献   

16.
Abstract— The presence of shocked quartz is one of the key lines of evidence for the impact origin of rocks. Crystallographic orientations of planar deformation feature (PDF) sets in shocked quartz have been used to constrain the peak shock pressure that these grains have experienced. So far no systematic and comparative studies of the various orientation measurement methods and their biases are available. Therefore, three shocked‐quartz‐bearing thin sections from a meta‐greywacke clast in breccia, a biotite‐gneiss, and a sandstone, respectively, were independently analyzed by three operators (two experienced and one inexperienced) using a four‐axis universal‐stage (U‐stage), in order to evaluate the quality, precision, repeatability, and representativeness of U‐stage measurements. Based on the indexing of PDF sets using a new version of the commonly used stereographic projection template, the study of 1751 PDF set orientations in 666 quartz grains in three different shocked rocks shows that differences in abundance and orientation of various PDF sets, as measured by the three separate operators, are rather limited. The precision of U‐stage measurements depends mainly on the number of PDF sets investigated, as the ability level of the operator (experienced versus inexperienced) is only responsible for minor deviations in the number of unindexed planes. The frequency percent of dominant PDF planes may vary by up to 20 percentage points (pp) or 81% for a given crystallographic orientation when only 25 sets are measured. When 100 PDF sets are measured, however, this deviation in dominant orientations is reduced to about 7 pp or 28%. We recommend the use of a new stereographic projection template, which plots the pole positions of five additional, commonly occurring PDF orientations, as it can allow indexing of up to 12 pp more PDF planes; these are planes that would previously be considered unindexed and potentially regarded as errors of measurement. Our results suggest that by following a strict measurement procedure, the reproducibility of U‐stage measurements is good and the results of different studies can be readily compared. However, it is critical that published PDF orientation histograms clearly define what type of frequency measurement is used, whether or not unindexed PDF sets are included in the frequency calculations, the numbers of grains and sets analyzed, and the relative proportions of each PDF set population that are combined in the histograms. This information appears to be essential for effectively comparing datasets from different studies.  相似文献   

17.
The results of high-resolution spectropolari metric observations (R = 60 000) of the B0.5-type subgiant ? PerA are reported. Regular components of line profile variations with the frequencies 3.82–12.99 d?1 are found. A possible relation between the non-radial pulsations of the star and the observed regular variations of the line profiles is shown. A wavelet analysis of the difference of line profiles in the spectrum of ? PerA is performed. The amplitude of the wavelet spectrum is found to have two maxima at 10–20 and 50–60 km/s velocity scales. It is suggested that the first maxi mum corresponds to the amplitude of fluctuations in the velocity field of large-scale motions in the non-radially pulsating photosphere of the star, whereas the second maximum is associated with the variation of the half widths of spectral line profiles. An upper limit for the effective magnetic field of the star is inferred.  相似文献   

18.
The behavior of quantum dust ion-acoustic (QDIA) shocks in a plasma including inertialess quantum electrons and positrons, classical cold ions and stationary negative dust grains are studied, using a quantum hydrodynamic model (QHD). The effect of dissipation due to the viscosity of ions is taken into account. The propagation of small but finite amplitude QDIA shocks is governed by the Kortoweg-de Vries-Burgers (KdVB) equation. The existence regions of oscillatory and monotonic shocks will depend on the quantum diffraction parameter (H) and dust density (d) as well as dissipation parameter (η 0). The effect of plasma parameters (d,H,η 0), on these structures is investigated. Results indicate that the thickness and height of monotonic shocks; oscillation amplitude of the oscillatory shock wave and it’s wavelength effectively are affected by these parameters. Additionally, the possibility of propagation of both compressive and rarefactive shocks is investigated. It is found that depending on some critical value of dust density (d c ), which is a function of H, compressive and rarefactive shock waves can’t propagate in model plasma. The present theory is applicable to analyze the formation of nonlinear structures at quantum scales in dense astrophysical objects.  相似文献   

19.
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20.
Current observational constraints on anisotropies in the CMB (Cosmic Microwave Background) and on the clustering of galaxies have considerably narrowed the range of acceptable models for galaxy formation. Observations of these anisotropies on intermediate and large angular scales provide the best constraint on the amplitude of very long wavelength density fluctuations. We present results from the Tenerife CMB fluctuation experiment (a Jodrell Bank-IAC collaboration) at intermediate angular scales (6 deg) which taken together with recently reported upper limits to fluctuations on small (arc min) angular scales constrain severely the spectral index of initial fluctuations in baryon dominated model universes. Constraints on adiabatic fluctuations in hot and cold dark matter models are also briefly discussed.  相似文献   

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