共查询到20条相似文献，搜索用时 203 毫秒
1.
Kam-Ching Leung 《Astrophysics and Space Science》1968,2(3):302-306
The relation between the amplitude of light m and the amplitude of the radial velocity 2K for Canis Majoris stars is investigated. A linear relationship between m and 2K is found. However, the two stars BW Vul and Sco, which have the largest radial velocity variations, do not seem to share this relationship. 相似文献
2.
V. M. Soundalgekar 《Astrophysics and Space Science》1979,66(1):223-233
A study of the two-dimensional unsteady flow of a viscous, incompressible fluid past an infinite vertical plate has been carried out under the following conditions: (1) constant suction at the plate, (2) wall temperature oscillating about a constant non-zero mean, and (3) constant free-stream. Approximate solutions to coupled non-linear equations governing the flow have been carried out for the transient velocity, the transient temperature, the amplitude and phase of the skin friction, and the rate of heat transfer. The velocity, temperature and amplitude are shown graphically whereas the numerical values of the phases are given in a table. It has been observed that the amplitude of the skin friction decreases with increasing (frequency) but increases with increasingG (Grashof number), while the amplitude of the rat of heat transfer increases with increasing . 相似文献
3.
A technique for predicting the amplitude of the solar cycle 总被引：3，自引：0，他引：3
R. J. Thompson 《Solar physics》1993,148(2):383-388
Predictions of the amplitude of the last three solar cycles have demonstrated the value and accuracy of the group of prediction methods known as the precursor techniques. These are based on a correlation between cycle amplitude and phenomena observed on the Sun, or originating from the Sun, during the declining phase of the cycle or at solar minimum. In many cases, precursor predictions make use of the long record of geomagnetic disturbance indices, assuming that these indices are indicative of solar phenomena such as the occurrence of coronal holes.This paper describes a precursor technique for predicting the amplitude of the solar cycle using geomagnetic indices. The technique is accurate — it would have predicted each of the last 11 cycles with a typical error of less than 20 in sunspot number. It has also advantage that a prediction of the lower limit of the amplitude can be made throughout the declining phase, this limit building to a final value at the onset of the new cycle. 相似文献
4.
Ya. N. Chkhikvadze 《Astrophysics》2003,46(4):489-495
Results of photoelectric observations in the Strömgren system of the Herbig Ae/Be star LkH 215 are presented. It is found that this star undergoes bursts. Two types of bursts are observed. The amplitude of the first type of burst increases with decreasing wavelength. In the second type of burst, the brightness amplitude has a maximum in the V band. 相似文献
5.
V. Letfus 《Solar physics》1994,149(2):405-411
Presuming a bimodal behaviour of even-odd solar cycle pairs (i.e., four modes designated asA, B, C, andD), we predict the amplitude of solar cycle 23. The bimodal properties include the dependence of maximum relative sunspot number (RM) on cycle rise time (TR) separately for odd-following and even cycles (both in two split modes), and the dependencies of odd-following on even cycles separately for cycle rise times and maximum relative sunspot numbers (each also split into two mode pairs). The procedure was first to identify the proper mode for cycle 22 (modeA), which then explicitly defines the mode for cycle 23 (modeC). The presumed mode-inherent relations were then used to estimate the rise time for cycle 23 (3.7 0.5 yr) and its maximum amplitude (195.1 17.1). A second estimate of maximum amplitude, based directly on a presumed mode-inherent relation between maximum amplitudes for even and odd cycle pairs, yields a somewhat lower value (181.3 44.3). Thus, the results of this analysis supports previous findings that cycle 23 may be one of the largest amplitude cycles ever observed. 相似文献
6.
Kam-Ching Leung 《Astrophysics and Space Science》1970,8(2):222-226
The observed positions of classical cepheids, RR Lyrae stars, Scuti stars and dwarf cepheids in the logg-logT
e plane form a continuous sequence, thereby defining the location of maximum instability. The amplitude ratio (the ratio of radial velocity amplitude to light amplitude) is small for variables at the upper end of the instability strip and increases almost linearly towards the lower end of the strip. The theory of radial pulsation predicts the trend of this correlation. 相似文献
7.
A heuristic model is proposed of the mean distances between the solar-system planets, their satellites and the primaries. The model is based on: (i) the concept of the solar system structure wave nature; (ii) the micro-mega analogy (MM analogy) of the micro- and megasystem structures, and (iii) the oscillator amplitude quantization phenomenon, occuring under wave action, discovered on the basis of the classical oscillations theory (Damgov et al., 1990, 1991).From the equation, describing the charge rotation under the action of an electromagnetic wave, an expression is obtained for the discrete set of probable stationary motion amplitudes. The discrete amplitude values — the quantization phenomenon — are defined by the argument values at the extreme points of the N-order Bessel functions. Using this expression, the mean related distances are computed from the solar system planets and the Saturn, Uranian and Jovian satellites to the primaries. 相似文献
8.
Robert M. Wilson 《Solar physics》1990,127(1):199-205
Statistically significant correlations exist between the size (maximum amplitude) of the sunspot cycle and, especially, the maximum value of the rate of rise during the ascending portion of the sunspot cycle, where the rate of rise is computed either as the difference in the month-to-month smoothed sunspot number values or as the average rate of growth in smoothed sunspot number from sunspot minimum. Based on the observed values of these quantities (equal to 10.6 and 4.63, respectively) as of early 1989, one infers that cycle 22's maximum amplitude will be about 175 ± 30 or 185 ± 10, respectively, where the error bars represent approximately twice the average error found during cycles 10–21 from the two fits. 相似文献
9.
We obtain an approximate analytic solution of a set of nonlinear model -dynamo equations. The reaction of the Lorentz force on the velocity shear which stretches and, hence, amplifies the magnetic field, is incorporated into the model. To single out the effect of the Lorentz force on the -effect, the effect of the Lorentz force on the -effect is neglected in this study. The solution represents a nonlinear oscillation with the amplitude and period determined by the dynamo numberN. The amplitude is proportional toN–1, while the period is almost exactly the same as the dissipation time of the unstable mode [proportional toN; note the linear oscillation period is proportional toN/(N–1) which is quite different for the solar situation whereN1]. 相似文献
10.
It is shown that a recent conclusion of Shivamaggi that the modulational instability of finite amplitude Alfvén waves arises when the density cavity travels at subsonic speeds, is incorrect. 相似文献
11.
R. K. Srivastava 《Astrophysics and Space Science》1989,154(2):333-336
FirstU, B, andV observations of UMa are presented. Light curves show light variations of varying amplitude. Colour indices also show small colour variations. 相似文献
12.
David M. Kipping 《Monthly notices of the Royal Astronomical Society》2009,392(1):181-189
As the number of known exoplanets continues to grow, the question as to whether such bodies harbour satellite systems has become one of increasing interest. In this paper, we explore the transit timing effects that should be detectable due to an exomoon and predict a new observable. We first consider transit time variation (TTV), where we update the model to include the effects of orbital eccentricity. We draw two key conclusions.
We go on to predict a new observable due to exomoons – transit duration variation (TDV). We derive the TDV amplitude and conclude that its amplitude is not only detectable, but the TDV signal will also provide two robust advantages.
- (i)
In order to maintain Hill stability, the orbital frequency of the exomoon will always be higher than the sampling frequency. Therefore, the period of the exomoon cannot be reliably determined from TTV, only a set of harmonic frequencies.
- (ii)
The TTV amplitude is ∝ M
S aS where MS is the exomoon mass and aS is the semimajor axis of the moon's orbit. Therefore, MS and aS cannot be separately determined.
We go on to predict a new observable due to exomoons – transit duration variation (TDV). We derive the TDV amplitude and conclude that its amplitude is not only detectable, but the TDV signal will also provide two robust advantages.
- (i)
The TDV amplitude is ∝ M
S a−1/2 S and therefore the ratio of TDV to TTV allows for MS and aS to be separately determined. - (ii)
TDV has a π/2 phase difference to the TTV signal, making it an excellent complementary technique.
13.
We have used a 5.5 min time-sequence of spectra in the Fe i lines 5576 (magnetically insensitive), 6301.5 and 6302.5 (magnetically sensitive) to study the association of concentrated magnetic regions and velocity in the quiet Sun. After the elimination of photospheric oscillations we found downflows of 100–300 m s –1, displaced by about 2 from the peaks of the magnetic field; this velocity is comparable to downflow velocity associated with the granulation and of the same order or smaller than the oscillation amplitude. Quasi-periodic time variations of the vertical component of the magnetic field up to ± 40% were also found with a period near 250 s, close to the values found for the velocity field. Finally we report a possible association of intensity maxima at the line center with peaks of the oscillation amplitude. 相似文献
14.
R. G. Giovanelli 《Solar physics》1979,62(2):253-268
A first-order theory is developed for the radiative dissipation of compressive waves in the chromosphere above T
min, where line radiation becomes dominant. The radiative relaxation time, which is the key to dissipation, is shown to depend on wave amplitude, falling greatly for amplitudes 2 km s–1 or more. For a given amplitude, dissipation is greatest for high frequencies, 0.1 s–1, periods 1 min. The observed short-period r.m.s. velocities ~2.4 km s–1 at the D1, level are adequate to provide dissipation balancing chromospheric emission losses.Predictions for the temperature-velocity phase difference and the phase velocity are compatible with observations. 相似文献
15.
In this paper it is derived that the libration of Mercury can be described by where Φ0 is the unknown libration amplitude, M is Mercury's mean anomaly and K=−9.483. Φ0 can be determined by comparing pairs of images of the same landmarks taken by an orbiter at different positions of Mercury. If the angle between the orbit plane of a polar orbiter and Mercury's line of periapsis is between −60° and 60° and if one landmark at the equator is imaged per day with a relative precision of , then the libration amplitude can be determined in two Mercury years (176 days) with an accuracy of or better, which is sufficient to answer the question whether Mercury has a solid or fluid core. 相似文献
16.
Max K. Wallis 《Earth, Moon, and Planets》1984,30(1):31-37
Hypervelocity impact sputter causes impulses substantially greater than the initial momenta of micro-grains of comet Halley's dust coma, the effective factor being discontinuous at the dust mass (0.2 g) that just penetrates the spacecraft bumper shield. Marginally non-penetrating grains determine the net drag and torque, calculated here for the Giotto shield and exposed components. The torque due to asymmetries induces a precession of the spacecraft axis, whose amplitude is solved for passage through the model dust coma, to find slowly damped oscillations of significant (1°) amplitude. 相似文献
17.
Stephan R. McCandliss Bruce Bohannan Carmelle Robert Anthony F. J. Moffat 《Astrophysics and Space Science》1994,221(1-2):155-167
The original temporal analysis of a 12 night spectral timeseries of WR-134 has been found to be flawed and a re-analysis shows that the line profile variations are indeed periodic. When combined with a 4 night timeseries taken 45 days earlier, a period near 2.27 d is found in periodograms of the Heii 5412 line centroid,rms line width, and line skew variations. When the emission line residuals are ordered as a function of phase, a sinuous feature appears to snake about the line center with an amplitude of ± 500 km s–1. This is 20 larger than the line centroid amplitude; the calculation of which is heavily weighted by static portions of the line profile. In addition to the snake, emission residuals appear that move away from line center on unbound trajectories and are thought to result from the interaction of a periodic driver with the unstable flow of the radiation driven wind. The nature of the periodic driver is a topic for discussion. 相似文献
18.
M. Breger 《Astrophysics and Space Science》1993,210(1-2):173-180
On short time-scales of under a year, the vast majority of Scuti stars studied in detail show completely regular multiperiodic pulsation. Nonradial pulsation is characterized by the excitation of a large number of modes with small amplitudes. Reports of short-term irregularity or nonperiodicity in the literature need to be examined carefully, since insufficient observational data can lead to an incorrect impression of irregularity. Some interesting cases of reported irregularities are examined.A few Scuti stars, such as 21 Mon, have shown stable variations with sudden mode switching to a new frequency spectrum. This situation might be an indication of deterministic chaos. However, the observational evidence for mode switching is still weak.One the other hand, the case for the existence of long-term amplitude and period changes is becoming quite convincing. Recently found examples of nonradial pulsators with long-term changes are 4 CVn, 44 Tau, Peg and HD 2724. (We note that other Scuti pulsators such as X Cae and
2 Tau, have shown no evidence for amplitude variations over the years.) Neither the amplitude nor the period changes are periodic, although irregular cycles with time scales between a few and twenty years can be seen. While the amplitude changes can be very large, the period changes are quite small. This property is common in nonlinear systems which lead to chaotic behavior. There exists observational evidence for relatively sudden period jumps changing the period by about 10–5 and/or slow period changes near dP/dt 10–9. These period changes are an order of magnitude larger than those expected from stellar evolution.The nonperiodic long-term changes are interpreted in terms of resonances between different nonradial modes. It is shown that a large number of the nonradial acoustic modes can be in resonance with other modes once the mode interaction terms, different radial orders and rotationalm-mode splitting are considered. These resonances are illustrated numerically by the use of pulsation model. Observational evidence is presented that these interaction modes exist in the low-frequency domain. 相似文献
19.
We present the analysis of spectrograms obtained during quiescence and during an ordinary outburst of the SU UMa type dwarf nova WX Hyi (ESO 3.6m telescope, B&C spectrograph with Image Disector Scanner, 171 Åmm–1, range 4000–7000 Å, time resolution 6min.). The radial velocities of these spectra have been discussed by Schoembs and Vogt (1981) who also derived the orbital elements of WX Hyi. The phasesmax refer to these elements. All velocities discussed here are with respect to the white dwarf, not to the center of mass of the binary system.Inquiescent state we did not find significant radial velocity variations. The equivalent widths W of the He I emission lines revealed periodic variations with an amplitude of 30%, maximal values of W were observed atmax=0.0...0.2. In contrast, the equivalent widths of the Balmer lines were not variable.Duringoutburst we found periodic radial velocity variations of the emission peak of H, H and He I 5875 with an amplitude of100 km s–1,max0.5. Also the broad Balmer absorption lines revealed periodic radial velocity variations, with a similar amplitude (max=0.3...0.5). The equivalent width of the H central emission peak varies with an amplitude of30%,max0.85. No variations of the equivalent width of the Balmer absorption lines were found.The outburst observations suggest that the preceeding part of the disc is brighter than the following one (in orbital motion). This is probably due to heating of the preceeding part by collisions with circumbinary matter, which seems to have an enhanced density in outburst as compared to the quiescent state. The emission lines are formed in outer layers or in a halo around the disc. The equivalent width variations can be interpreted in terms of interactions between this halo and the optically thick part of the disc.A more detailed discussion of the data is being published elsewhere.Paper presented at the IAU Colloquium No. 93 on Cataclysmic Variables. Recent Multi-Frequency Observations and Theoretical Developments, held at Dr. Remeis-Sternwarte Bamberg, F.R.G., 16–19 June, 1986 相似文献
20.
L. I. Antipova 《Astrophysics and Space Science》1987,131(1-2):453-459
The period-amplitude relation and the period-energy relation for dwarf novae and novae are discussed. The total outbursts energy is shown to be a more suitable characteristic of the outburst than its amplitude.Paper presented at the IAU Colloquium No. 93 on Cataclysmic Variables. Recent Multi-Frequency Observations and Theoretical Developments, held at Dr. Remeis-Sternwarte Bamberg, F.R.G., 16–19 June, 1986. 相似文献