共查询到20条相似文献,搜索用时 15 毫秒
1.
The application of the fast-Fourier-transform (FFT) algorithm to calculating one-dimensional and bi-dimensional (temporal and spatial), power and cross-power (coherence and phase) spectra is examined for solar photospheric fluctuations. Alternative methods for smoothing raw spectra, direct averaging (employing various weights) and indirect truncation of the correlation function, are compared, and indirect smoothing is compared with spectra calculated by mean-lagged-product (MLP) methods. Besides providing the raw spectrum, FFT techniques easily allow computing a series of spectra with varying amounts of smoothing. From these spectra a range of satisfactory compromise between resolution and stability can be determined which helps in the interpretation of spectral trends, and in identifying more clearly the existence and significance of spectral features. For bi-dimensional spectra presented as contour plots, this range of satisfactory smoothing can be restricted, particularly when spectral trends must be represented by small-scale contours. Equivalent spectra (i.e. comparable equivalent degrees of freedom) computed or smoothed by different methods have minor, but not negligible, differences. Examination of these differences favors computing of FFT spectra smoothed by averaging for photospheric fluctuations. 相似文献
2.
Residual intensity fluctuation measurements within the wings of the 5183.6 Mgi b1 line, obtained from two, high-resolution, high-dispersion, Sacramento Peak Observatory spectrograms, have been subtracted from intensity fluctuations in the adjacent continuum in order to isolate fluctuations associated exclusively with line formation. The useable spectral range for studying these lineformation fluctuations is restricted to wavelengths between 1040 and 7170 km because the subtraction increases the relative importance of noise and large-scale photographic variations across the spectrograms could not be completely removed. Power and cross-power (coherence and phase) spectra proved to be valuable diagnostic tools in isolating line-formation fluctuations.Over this spectral range, the line-formation fluctuations are characterized by flat power spectra as compared to those for continuum fluctuations, appreciable fluctuation rms relative to that for continuum fluctuations, and the necessity to multiply the wing fluctuations by a factor 0.95 min 1.00 to most effectively isolate these fluctuations (Figures 3 and 4). That continuum fluctuations are modified in shape but otherwise not drastically changed in the line wings explains the flat spectrum. The relative rms's vary from 0.34 in the inner wing to 0.22 in the outer. The range of possible values for
min results from uncertainties in the photographic density-residual intensity calibration. 相似文献
3.
Frank N. Edmonds Jr. 《Solar physics》1975,44(2):293-297
Synthetic one-dimensional scans of brightness fluctuations are generated from intergranulegranule profiles (IGP), which approximate observed scans of granulation fluctuations except that the local (i.e. IGP) mean intensity is kept constant. Comparing the power spectrum of such scans with the power spectrum of observed scans shows that nearly two thirds of the low-wavenumber (k < 0.0025 km-1) granulation power is due to this variable mean effect. This result favors the interpretation of granulation as turbulent thermal convection but cannot rule out the laminar convection interpretation. 相似文献
4.
Frank N. Edmonds Jr. 《Solar physics》1967,1(1):5-15
Amplitude distributions, which are nearly Gaussian, have been calculated for radial velocity, continuum brightness, spectral line equivalent width and spectral line central residual intensity fluctuations measured from high-dispersion high-resolution spectrograms taken at the center of the solar disk. The RMS and skewness S for each distribution have been calculated in a manner which allows testing of the homogeneity of the granulation pattern (i.e. variations in its statistics across the solar disk and with time). Pattern inhomogeneity across the disk is strongly indicated, and further evidence suggesting appreciable pattern persistence over time intervals 15 minutes is presented. The possibilities for investigations of S and its associated bi-spectrum are discussed. The qualitative values of S obtained are shown not to be due to unusually bright, rising granules (though a statistical tendency towards such granules is possible). An attempt to explain S for continuum brightness fluctuations in terms of the nonlinear effects of Planckian emission and opacity fluctuations in a stratified photosphere, leads to contradiction with the measured amplitude distributions, a contradiction which is probably due to an oversimplified treatment of radiative transfer in an inhomogeneous photosphere. 相似文献
5.
A new value of the solar photospheric abundance of iron, independent of line-shape parameters, is derived. Our analysis is based on a study of 40 weak infrared lines (0.85<λ<2.5 μ) for which theoretical oscillator strengths (calculated with configuration interactions taken into account) have recently been computed by Kurucz (1974). The abundance obtained, A Fe = 7.57±0.11 (in the usual scale where log N H = 12.00) is in agreement with the ‘high’ solar values recently reported in the literature and with the meteoritic abundance. 相似文献
6.
Audouin Dollfus 《Solar physics》1990,129(1):1-30
The coherent 5-min photospheric pressure oscillations with spherical harmonic degrees in the range 100 <l< 1000 were directly imaged over the photosphere with the monochromatic solar telescope FPSS at Meudon Observatory. Movie films were obtained with images spatially filtered to select sizes of increasing wave numbers (or l). Areas with ephemeral concentrations of coherent waves evolve in shape and may move horizontally with velocities of several tenths of km s–1. When a large number of waves are interacting, the maximum vertical velocity V
max of the pulsation reaches around 1000 m s–1, irrespective of the size. Extrapolation to the ideal case of a single isolated wave gives V
max proportional to size. For the areas of the smallest scale measured (l = 1000), when about 100 waves are interacting, V
max is found to be 260 + 25 m s–1 at an altitude of 210 km above the reference level 5000 = 1 and increases vertically with a scale height of 750 ± 400 km. 相似文献
7.
E. Caffau R. Faraggiana H.‐G. Ludwig P. Bonifacio M. Steffen 《Astronomische Nachrichten》2011,332(2):128-139
Zirconium (Zr), together with strontium and yttrium, is an important element in the understanding of the Galactic nucleosynthesis. In fact, the triad Sr‐Y‐Zr constitutes the first peak of s‐process elements. Despite its general relevance not many studies of the solar abundance of Zr were conducted. We derive the zirconium abundance in the solar photosphere with the same CO5BOLD hydrodynamical model of the solar atmosphere that we previously used to investigate the abundances of C‐N‐O. We review the zirconium lines available in the observed solar spectra and select a sample of lines to determine the zirconium abundance, considering lines of neutral and singly ionised zirconium. We apply different line profile fitting strategies for a reliable analysis of Zr lines that are blended by lines of other elements. The abundance obtained from lines of neutral zirconium is very uncertain because these lines are commonly blended and weak in the solar spectrum. However, we believe that some lines of ionised zirconium are reliable abundance indicators. Restricting the set to Zr II lines, from the CO5BOLD 3D model atmosphere we derive A (Zr) = 2.62 ± 0.06, where the quoted error is the RMS line‐to‐line scatter (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
8.
Two-dimensional spatial autocorrelation functions and power spectral density distributions were obtained from high-resolution velocity spectroheliograms. Although the autocorrelation functions indicate the existence of velocity cells of size roughly 2500 to 3500 km, the power spectra fail to reveal them because the cells are not strictly spatially periodic. 相似文献
9.
S. S. Hasan 《Astrophysics and Space Science》1996,243(1):155-158
The interaction of an intense flux tube, extending vertically through the photosphere, with p-modes in the ambient medium is modelled by solving the time dependent MHD equations in the thin flux tube approximation. It is found that a resonant interaction can occur, which leads to the excitation of flux tube oscillations with large amplitudes. The resonance is not as sharp as in the case of an unstratified atmosphere, but is broadened by a factor proportional toH
–2, whereH is the local pressure scale height. In addition, the inclusion of radiative transport leads to a decrease in the amplitude of the oscillations, but does not qualitatively change the nature of the interaction. 相似文献
10.
The observational difficulties of obtaining the magnetic field distribution in the chromosphere and corona of the Sun has led to methods of extending photospheric magnetic measurements into the solar atmosphere by mathematical procedures. A new approach to this problem presented here is that a constant alpha force-free field can be uniquely determined from the tangential components of the measured photospheric flux alone. The vector magnetographs now provide measurements of both the solar photospheric tangential and the longitudinal magnetic field. This paper presents derivations for the computation of the solar magnetic field from these type of measurements. The fields considered are assumed to be a constant alpha force-free fields or equivalent, producing vanishing Lorentz forces. Consequently, magnetic field lines and currents are related by a constant and hence show an identical distribution. The magnetic field above simple solar regions are described from the solution of the field equations. 相似文献
11.
A numerical simulation is performed to investigate the prominence formation in a magnetic arcade by photospheric shearing motions. A two-and-a-half-dimensional magnetohydrodynamic (MHD) code is used, in which the gravitational force, radiative cooling, thermal conduction and a simplified form of coronal heating are included. It is found that a footpoint shear induces an expansion of the magnetic arcade and cooling of the plasma in it. Simultaneously the denser material from the lower part of the arcade is pulled up by the expanding field lines. A local enhancement of radiative cooling is thus effected, which leads to the onset of thermal instability and the condensation of coronal plasma. The condensed material grows vertically to form a sheet-like structure making dips on field lines, leading to the formation of the Kippenhahn- Schlüter type prominence. The mass of the prominence is found to be supplied not only by the condensation of the material in the vicinity but also by the siphon-type upflows. The upward growth of the vertical sheet-structure of the prominence is saturated at a certain stage and the newly condensed material is found to slide down from above the prominence along magnetic field lines. This drainage of material leads to the formation of an arc-shaped cavity of low density and low pressure around the prominence. The problem of force and heat balance is addressed and the prominence is found to be not in a static equilibrium but in a dynamic interaction with its environment. 相似文献
12.
P. D. Singh 《Astrophysics and Space Science》1984,102(2):287-293
The24MgH+ (A
1+ –X
1+) molecular lines have been identified in the photospheric spectrum. The rotational excitation temperature determined from the analysis of molecular line intensities of24MgH+ is found to be of the order of 4850 K which corresponds to the photospheric temperature of the Sun. The CNDO/2 dipole moments of24MgH+ for internuclear distance range: (1.3–2.1) Å in theX
1+ state can be approximated byM(R)=4.92+1.33R. Estimations for the spontaneous emission Einstein coefficients (A
v v
) and the absorption oscillator strengths (f
v v
) for the (1, 0), (2, 0), and (2, 1) transitions in theX
1+ state of the24MgH+ ion are also made.Work partially supported by the CNPq, Brasilia under contract number 30.4076/77. 相似文献
13.
We investigate the structure of convective flows in the solar photosphere on subgranulation scales. The solar granulation pattern is reproduced by solving the inverse problem of nonequilibrium radiation transfer on the basis of the profiles of the neutral iron line λ 523.42 nm. The wave motions are excluded by the k-ω filtration. The line-of-sight velocity has an asymmetric distribution inside the convective flows in large granules (1.5″ and larger) in the lower photosphere and at the bottom of the middle photosphere. This asymmetry is weaker in the upper photosphere. For smaller flows the distribution is more symmetric at all heights. The asymmetry of the temperature distribution is less pronounced. Large convective flows were found to have a fine structure: they are fragmentized into several smaller flows. The fine structure of large flows and spatial smearing are responsible for the observed asymmetry of the convection velocity distribution inside flows. 相似文献
14.
An analysis of relationships between latitudinal fine structures of the photospheric plasma differential rotation and solar activity shows that sunspot activity seems to be lower (as measured by the number and extension of sunspot groups) at latitudes where minima of angular velocity appear. 相似文献
15.
Methods for the determination of the average optical depth of formation of weak Fraunhofer lines are compared, and their relative merits are discussed. Distinction should be made between the region of origin of the emergent radiation, and of the line depression. For weak or fairly weak lines the average optical depth of formation of the line depression is the relevant quantity; it should be determined by using a computational scheme based on the classical weighting functions of line formation; other methods give physically unsignificant or conflicting results.
相似文献16.
The detailed study of the possible presence of four [Niii] lines in solar absorption leads to an abundanceA
ni = logN
ni = 6.30±0.30 (in the usual scale where logN
H = 12.00), in agreement with the coronal and meteoritic values.On leave from Institut d'Astrophysique, Université de Liège. 相似文献
17.
The flare-related, persistent and abrupt changes in the photospheric magnetic field have been reported by many authors during recent years. These bewildering observational results pose a challenge to the current flare theories in which the photospheric magnetic field usually remains unchanged in the eruption. In this paper, changes in the photosphere magnetic field during the solar eruption are investigated based on the catastrophe model. The results indicate that the projection effect is an important source that yields the change in the observed photospheric magnetic field in the line-of-sight. Furthermore one may observe the change in the normal component of magnetic field if the spectrum line used to measure the photospheric magnetic field does not exactly come from the photospheric surface. Our results also show that the significance of selecting the correct spectral lines to study the photospheric field becomes more apparent for the magnetic configurations with complex boundary condition (or background field). 相似文献
18.
P. Persi 《Solar physics》1975,43(1):39-47
A new numerical method for the analysis of the high dispersion photospheric spectrum is described. In particular the method is applied to study the C2(0, 0) d 3 Πg-a a Πu molecular band. From measurements of the equivalent widths of C2 lines, a rotational temperature of 4450 ± 305 K is obtained, and the band intensity log W 0 /S 0 = ?0.051 ± 0.101 is found. 相似文献
19.
N. S. Shilova 《Solar System Research》2006,40(5):437-440
The cells of photospheric background magnetic fields during Carrington rotation 2009 in October–November 2003 are considered. The small number of large sunspots and the high activity on the Sun in this period allow the correspondence between the activity of background field cells (flares) and the appearance of coronal mass ejections (CMEs) observed with the LASCO coronagraphs to be established without statistical analyses. The sunspots of opposite polarities in one background field cell are shown to serve as the legs of the same CME. The separation between them is close to 30°. 相似文献
20.
Z. Mouradian 《Astrophysics》1995,38(4):280-285
A review of physical properties of various regions of the solar atmosphere is given for both quiet and active sun. More typical morphological and spectral features for each region are presented. Possible genetic relations between solar structures are indicated.Published in Astrofizika, Vol. 38, No. 4, pp. 508–518, October–December, 1995. 相似文献