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1.
A. V. Getling 《Solar physics》2006,239(1-2):93-111
Two series of solar-granulation images – the La Palma series of 5 June 1993 and the SOHO MDI series of 17 – 18 January 1997
– are analysed both qualitatively and quantitatively. New evidence is presented for the existence of long-lived, quasi-regular
structures (first reported by Getling and Brandt, Astron. Astrophys. 382, L5 (paper I), 2002), which no longer appear unusual in images averaged over 1 – 2-hour time intervals. Such structures appear
as families of light and dark concentric rings or families of light and dark parallel strips (“ridges” and “trenches” in the
brightness distributions). In some cases, rings are combined with radial “spokes” and can thus form “web” patterns. The characteristic
width of a ridge or trench is somewhat larger than the typical size of granules. Running-average movies constructed from the
series of images are used to seek such structures. An algorithm is developed to obtain, for automatically selected centres,
the radial distributions of the azimuthally averaged intensity, which highlight the concentric-ring patterns. We also present
a time-averaged granulation image processed with a software package intended for the detection of geological structures in
aerospace images. A technique of running-average-based correlations between the brightness variations at various points of
the granular field is developed and indications are found for a dynamical link between the emergence and sinking of hot and
cool parcels of the solar plasma. In particular, such a correlation analysis confirms our suggestion that granules – overheated
blobs – may repeatedly emerge on the solar surface. Based on our study, the critical remarks by Rast (Astron. Astrophys. 392, L13, 2002) on the original paper by Getling and Brandt (paper I) can be dismissed. 相似文献
2.
We use an innovative research technique to analyze combined images from the Coronal Diagnostic Spectrometer (CDS) on the Solar and Heliospheric Observatory (SOHO) and the Transition Region and Coronal Explorer (TRACE). We produce a high spatial and temporal resolution simulated CDS raster or “composite” map from TRACE data and use
this composite map to jointly analyze data from both instruments. We show some of the advantages of using the “composite”
map method for coronal loop studies. We investigate two postflare loop structures. We find cool material (250 000 K) concentrated
at the tips or apex of the loops. This material is found to be above its scale height and therefore not in hydrostatic equilibrium.
The exposure times of the composite map and TRACE images are used to give an estimate of another loop’s cooling time. The
contribution to the emission in the TRACE images for the spectral lines present in its narrow passband is estimated by using
the CDS spectral data and CHIANTI to derive synthetic spectra. We obtain cospatial and cotemporal data collected by both instruments
in SOHO Joint Observations Program (JOP) 146 and show how the combination of these data can be utilized to obtain more accurate
measurements of coronal plasmas than if analyzed individually.
Electronic Supplementary Material The online version of this article () contains supplementary material, which is available to authorized users. 相似文献
3.
Periodic Appearance of Coronal Holes and the Related Variation of Solar Wind Parameters 总被引：1，自引：0，他引：1
We compared the variability of coronal hole (CH) areas (determined from daily GOES/SXI images) with solar wind (daily ACE
data) and geomagnetic parameters for the time span 25 January 2005 until 11 September 2005 (late declining phase of solar
cycle 23). Applying wavelet spectral analysis, a clear 9-day period is found in the CH time series. The GOES/SXI image sequence
suggests that this periodic variation is caused by a mutual triangular distribution of CHs ∼120° apart in longitude. From
solar wind parameters a 9-day periodicity was obtained as well, simultaneously with the 9-day period in the CH area time series.
These findings provide strong evidence that the 9-day period in solar wind parameters, showing up as higher harmonic of the
solar rotation frequency, is caused by the “periodic” longitudinal distribution of CHs on the Sun recurring for several solar
rotations. The shape of the wavelet spectrum from the Dst index matches only weakly with that from the CH areas and is more similar to the wavelet spectrum of the solar wind magnetic
field magnitude. The distinct 9-day period does not show up in sunspot group areas which gives further evidence that the solar
wind modulation is strongly related to CH areas but not to active region complexes. The wavelet power spectra for the whole
ACE data range (∼1998 – 2006) suggest that the 9-day period is not a singular phenomenon occurring only during a specific
time range close to solar minimum but is occasionally also present during the maximum and decay phase of solar cycle 23. The
main periods correspond to the solar rotation (27d) as well as to the second (13.5d) and third (9d) harmonic.
Electronic Supplementary Material The online version of this article () contains supplementary material, which is available to authorized users. 相似文献
4.
A dm-radio emission with fiber bursts observed on 11 July 2005 was analyzed using wavelet filtration and spectral methods.
In filtered radio spectra we found structures with different characteristic period P and frequency drift FD: i) fiber substructures (composed of dot emissions) with P
1≈ 0.5 s, FD1=− 87 MHz s−1 on average, ii) fiber structures with P
2≈1.9 s, and iii) drifting structures with P
3≈81.4 s, FD2=− 8.7, + 98.5, and − 21.8 MHz s−1. In the wavelet spectra we recognized patterns having the form of tadpoles. They were detected with the same characteristic
periods P as found for the filtered structures. The frequency drift of the tadpole heads is found to be equal to the frequency drift
of some groups of fibers for the long-period wavelet tadpoles (P
3) and to the frequency drift of individual fibers for the short-period tadpoles (P
2). Considering these wavelet tadpoles as signatures of propagating magnetoacoustic wave trains, the results indicate the presence
of several wave trains in the fibers’ source. While the long-period wave trains trigger or modulate a whole group of fibers,
the short-period ones look like being connected with individual fiber bursts. This result supports the model of fibers based
on magnetoacoustic waves. Using a density model of the solar atmosphere we derived the velocities of the magnetoacoustic waves,
107 and 562 km s−1, and setting them equal to the Alfvén ones we estimated the magnetic field in the source of fiber bursts as 10.7 and 47.8 G. 相似文献
5.
I. D. Karachentsev D. I. Makarov V. E. Karachentseva O. V. Melnyk 《Astrophysical Bulletin》2011,66(1):1-27
We present a catalog of 520 most isolated nearby galaxies with angular velocities V
LG
< 3500 km/s, covering the entire sky. This population of “space orphans” makes up 4.8% among 10 900 galaxies with measured
radial velocities. We describe the isolation criterion used to select our sample, called the “Local Orphan Galaxies”(LOG),
and discuss their basic optical and HI properties. A half of the LOG catalog is occupied by the Sdm, Im and Ir morphological
type galaxies without a bulge. The median ratio M
gas/M
star in the LOG galaxies exceeds 1. The distribution of the catalog galaxies on the sky looks uniform with some signatures of
a weak clustering on the scale of about 0.5 Mpc. The LOG galaxies are located in the regions where the mean local density
of matter is approximately 50 times lower than the mean global density. We indicate a number of LOG galaxies with distorted
structures, which may be the consequence of interaction of isolated galaxies with massive dark objects. 相似文献
6.
Variations in total solar irradiance (TSI) correlate well with changes in projected area of photospheric magnetic flux tubes
associated with dark sunspots and bright faculae in active regions and network. This correlation does not, however, rule out
possible TSI contributions from photospheric brightness inhomogeneities located outside flux tubes and spatially correlated with them. Previous reconstructions of TSI report agreement with radiometry that seems to rule out significant “extra-flux-tube” contributions.
We show that these reconstructions are more sensitive to the facular contrasts used than has been generally recognized. Measurements
with the Solar Bolometric Imager (SBI) provide the first reliable support for the relatively high, wide-band, disk-center
contrasts required to produce 10% rms agreement. Longer term bolometric imaging will be required to determine whether the
small but systematic TSI residuals we see here are caused by remaining errors in spot and facular areas and contrasts or by
extra-flux-tube brightness structures such as bright rings around sunspots or “convective stirring” around active regions. 相似文献
7.
Francisco Javier Muñoz-Almaraz Emilio Freire Jorge Galan-Vioque Andre Vanderbauwhede 《Celestial Mechanics and Dynamical Astronomy》2007,97(1):17-47
In this paper we introduce the concept of a quasi-submersive mapping between two finite-dimensional spaces, we obtain the
main properties of such mappings, and we introduce “normality conditions” under which a particular class of so-called “constrained
mappings” are quasi-submersive at their zeros. Our main application is concerned with the continuation properties of normal
doubly symmetric orbits in time-reversible systems with one or more first integrals. As examples we study the continuation
of the figure-eight and the supereight choreographies in the N-body problem. 相似文献
8.
“EIT waves” are a wavelike phenomenon propagating in the corona, which was initially observed in the extreme ultraviolet (EUV)
wavelength by the EUV Imaging Telescope (EIT). Their nature is still elusive, with the debate on-going between fast-mode wave
model and non-wave model. In order to distinguish between these models, we investigate the relation between the EIT wave velocity
and the local magnetic field in the corona. It is found that the two parameters show significant negative correlation in most
of the EIT wave fronts, i.e., the EIT wave propagates more slowly in the regions of stronger magnetic field. Such a result poses a big challenge to the
fast-mode wave model, which would predict a strong positive correlation between the two parameters. However, it is demonstrated
that such a result can be explained by the fieldline stretching model, i.e., that “EIT waves” are the propagation of apparent brightenings, which are generated by successive stretching of closed magnetic
field lines pushed by the erupting flux rope during coronal mass ejections (CMEs). 相似文献
9.
Laurent Koechlin Denis Serre Gerald K. Skinner Peter Von Ballmoos Thomas Crouzil 《Experimental Astronomy》2005,20(1-3):307-315
The light deviation caused by the gravitational potential in the vicinity of the sun could be used as a means of focussing radiation that cannot be focussed easily otherwise. The gravitational lens formed by the sun is not stigmatic, but does have the advantage of being achromatic and acts identically on all types of mass-less radiations. For a source at infinity, its geometrical characteristics present a “caustic” line starting at 550 astronomical units (UA) downstream from the sun. In a plane perpendicular to that caustic line, images of distant objects are formed.The perturbations by the solar corona plasma will significantly blur electromagnetic radiation for wavelengths longer than those of the IR domain. At shorter wavelengths, for example the γ domain, the focussing process could lead to 108 amplification factors. In order to reach the regions where images are formed, long distance space missions are necessary. Once launched, missions of this type would be dedicated to a single field. Some possible targets are considered, such as Sagitarius A observed in X and γ rays.In this paper we study the point spread function (PSF) of the sun as a gravitational lens. Taking into account perturbations by the planets, the non sphericity of the sun and coronal plasma index, we derive limits within which such observations could be possible. 相似文献
10.
Markus J. Aschwanden 《Solar physics》2005,228(1-2):339-358
EUV images show the solar corona in a typical temperature range of T >rsim 1 MK, which encompasses the most common coronal structures: loops, filaments, and other magnetic structures in active regions,
the quiet Sun, and coronal holes. Quantitative analysis increasingly demands automated 2D feature recognition and 3D reconstruction,
in order to localize, track, and monitor the evolution of such coronal structures. We discuss numerical tools that “fingerprint”
curvi-linear 1D features (e.g., loops and filaments). We discuss existing finger-printing algorithms, such as the brightness-gradient
method, the oriented-connectivity method, stereoscopic methods, time-differencing, and space–time feature recognition. We
discuss improved 2D feature recognition and 3D reconstruction techniques that make use of additional a priori constraints, using guidance from magnetic field extrapolations, curvature radii constraints, and acceleration and velocity
constraints in time-dependent image sequences. Applications of these algorithms aid the analysis of SOHO/EIT, TRACE, and STEREO/SECCHI
data, such as disentangling, 3D reconstruction, and hydrodynamic modeling of coronal loops, postflare loops, filaments, prominences,
and 3D reconstruction of the coronal magnetic field in general. 相似文献
11.
The “circumpolar survey” technique allowed us to achieve a rather high antenna temperature sensitivity of 0.5 mK at 6 cm on
a fixed antenna with a relatively narrow frequency resolution band (600 kHz) and an angular resolution of 45″ × 7′. Starting
from 2007 we use a Fourier spectral analyzer with a survey band 10 times broader than that of previous observations. This
upgrade allowed us to rapidly perform repeated test observations, which confirmed the power-law nature and the frequency structure
of spatial spectra in two strips in the vicinity of the celestial pole in the 4′–16′ interval of angular periods. These observations
also showed that the Galactic CH molecular line that was by chance captured in our survey strip (Λ-doubling of rotational
transition) has nothing to do with the emission spectra we obtained. The angular pattern of emission in two main lines of
Λ-doubling (4847.84 and 4870.12 MHz) is absolutely different, whereas there is practically no maser amplification in the CH
line to explain this fact. Our observations also confirm the H110 α line (4874.157 MHz), which forms in the tenuous ionized Galactic hydrogen at such relatively high latitudes. Other features
of the spatial spectra also appear to be quite real, although their interpretation remains unclear and requires further studies. 相似文献
12.
The problem of lithium in chemically peculiar Ap-CP stars has been the subject of debate for many years. The main reason for
this is a lack of spectral observations of Ap stars in the neighborhood of the lithium resonance doublet Li I 6708 Å. An international
cooperation project on “Lithium in cool CP stars with magnetic fields” was started in 1996. Systematic observations of CP
stars in spectral regions of the 6708 Å and 6103 Å lines at the ZTSh (CrAO), CAT (ESO), Feros (ESO), and the 74″ telescope
of the Mount Stromlo Observatory (Australia) have been used to analyze spectra of several CP stars studied by the way the
6708 Å lithium line varies with the stars’ rotational phase. Monitoring of the spectra of the oscillating CP stars (group
I) HD 83368, HD 60435, and HD 3980, for which significant Doppler shifts of the Li I 6708 Å line are observed led to the discovery
of “lithium spots” on the surface of these stars whose positions are related to the magnetic field structure. Models of the
surfaces of these stars with the special program “ROTATE” based on the profiles of the Li I 6708 Å line are used to estimate
the size of the spots, their positions on the stars’ surface, and the lithium abundances in these spots. A detailed analysis
and modelling of the spectra of slowly rotating oscillating CP stars with strong, invariant lithium 6708 Å emission, including
blending with lines of the rare earth elements, reveals an enhanced lithium abundance, with the abundance determined from
the lithium 6103 Å line being higher than that determined from the 6708 Å line for all the stars. This may indicate vertical
stratification of lithium in the atmospheres of CP stars with an anomalous isotopic composition (6Li/7Li = 0.2–0.5). HD 101065, an ultraslow rotator (vsini ≈ 1.5) visible from the poles and with powerful oscillations which cause pulsating line broadening in its spectrum, is unique
among these stars. The amount of lithium in the atmosphere of HD 101065 logN(Li) = 3.1 on a scale of logN(H) = 12.0 and the isotope ratio 6Li/7Li ≈ 0.3. The high estimates of 6Li/7Li may be explained by the production of lithium in spallation reactions and the preservation of surface 6Li and 7Li by strong magnetic fields in the upper layers of the atmosphere near the magnetic poles.
__________
Translated from Astrofizika, Vol. 50, No. 3, pp. 463–492 (August 2007). 相似文献
13.
Ai-Ying Zhou 《Astrophysics and Space Science》2006,301(1-4):11-20
The variability of period and amplitude of the high-amplitude δ Scuti star YZ Boo was thoroughly investigated based on a comprehensive
analysis of new time-series photometry and other available data. Fourier analysis, O–Cdiagram, and wavelet analysis establish a clear picture for the star's time-dependent behavior in period and amplitude. We
detected no additional frequencies being intrinsic to the variable or caused by amplitude/frequency modulation confirming
its mono-periodicity. We reveal the pulsation of YZ Boo is quite stable in both period and amplitude over the past 50 years.
Short-term variations at cycle level including “anomalous cycles” are present clearly, while long-term variations in period
and amplitude at annual base are insignificant. However, we note an increment from 2000 to 2003 in both period and amplitude.
In 2000 the amplitude reached the lowest. This is indicated by the Fourier and wavelet results. In the long term, O–Cfits and wavelet analysis agree with the Fourier results that the period change of YZ Boo is still inconclusive. 相似文献
14.
We present the observations of the Irr galaxy IC 10 at the 6-m SAO telescope with the panoramic Multi-Pupil Fiber Spectrograph
(MPFS). Based on the results of these observations and our long-slit spectroscopy performed previously, we have investigated
the ionized-gas emission spectrum in the region of intense star formation and refined the gas metallicity estimates. We show
that the “diagnostic diagrams” constructed from our observations agree best with the new improved ionization models by Martin-Manjon
et al. Using these models, we have determined the electron density and gas ionization parameter and ionizing-cluster characteristics,
the age and mass, from the spectra of the investigated HII regions. The cluster ages and masses are shown to be within the
ranges 2.5–5 Myr and (0.2–1) × 105
M
⊗, respectively. 相似文献
15.
We summarize the response of the galactic cosmic ray (CGR) intensity to the passage of the more than 300 interplanetary coronal
mass ejections (ICMEs) and their associated shocks that passed the Earth during 1995 – 2009, a period that encompasses the
whole of Solar Cycle 23. In ∼ 80% of cases, the GCR intensity decreased during the passage of these structures, i.e., a “Forbush decrease” occurred, while in ∼ 10% there was no significant change. In the remaining cases, the GCR intensity
increased. Where there was an intensity decrease, minimum intensity was observed inside the ICME in ∼ 90% of these events.
The observations confirm the role of both post-shock regions and ICMEs in the generation of these decreases, consistent with
many previous studies, but contrary to the conclusion of Reames, Kahler, and Tylka (Astrophys. J. Lett. 700, L199, 2009) who, from examining a subset of ICMEs with flux-rope-like magnetic fields (magnetic clouds) argued that these are “open
structures” that allow free access of particles including GCRs to their interior. In fact, we find that magnetic clouds are
more likely to participate in the deepest GCR decreases than ICMEs that are not magnetic clouds. 相似文献
16.
José Antonio Belinchón 《Astrophysics and Space Science》2009,323(3):307-315
We study a massive cosmic strings with BII symmetries cosmological models in two contexts. The first of them is the standard
one with a barotropic equation of state. In the second one we explore the possibility of taking into account variable “constants”
(G and Λ). Both models are studied under the self-similar hypothesis. We put special emphasis in calculating the numerical values
for the equations of state. We find that for ω∈(0,1], G, is a growing time function while Λ, behaves as positive decreasing time function. If ω=0, both “constants”, G and Λ, behave as true constants. 相似文献
17.
In this paper we study the evolution of a LRS Bianchi I Universe, filled with a bulk viscous cosmological fluid in the presence
of time varying constants “but” taking into account the effects of a c-variable into the curvature tensor. We find that the only physical models are those which “constants” G and c are growing functions on time t, while the cosmological constant Λ is a negative decreasing function. In such solutions the energy density obeys the ultrastiff
matter equation of state i.e. ω = 1. 相似文献
18.
Helioseismic techniques such as ring-diagram analysis have often been used to determine the subsurface structural differences
between solar active and quiet regions. Results obtained by inverting the frequency differences between the regions are usually
interpreted as the sound-speed differences between them. These in turn are used as a measure of temperature and magnetic-field
strength differences between the two regions. In this paper we first show that the “sound-speed” difference obtained from
inversions is actually a combination of sound-speed difference and a magnetic component. Hence, the inversion result is not
directly related to the thermal structure. Next, using solar models that include magnetic fields, we develop a formulation
to use the inversion results to infer the differences in the magnetic and thermal structures between active and quiet regions.
We then apply our technique to existing structure inversion results for different pairs of active and quiet regions. We find
that the effect of magnetic fields is strongest in a shallow region above 0.985R
⊙ and that the strengths of magnetic-field effects at the surface and in the deeper (r<0.98R
⊙) layers are inversely related (i.e., the stronger the surface magnetic field the smaller the magnetic effects in the deeper layers, and vice versa). We also find that the magnetic effects in the deeper layers are the strongest in the quiet regions, consistent with the
fact that these are basically regions with weakest magnetic fields at the surface. Because the quiet regions were selected
to precede or follow their companion active regions, the results could have implications about the evolution of magnetic fields
under active regions. 相似文献
19.
We discuss early results derived from an algorithm that automates the detection, cataloging, and analysis of extreme-ultraviolet
(EUV) “bright points” (BP) from 9 years of data acquired by the Extreme-ultraviolet Imaging Telescope (EIT) on the Solar and
Heliospheric Observatory (SOHO). The algorithm relies upon the computation of a map of “intensity significance”; this then
contains the location of the EUV BPs. By mapping the location of BPs in each image and linking them through long sequences
of EIT images we can describe the temporal and spatial variations of the 1.3× 108 EUV BPs observed by SOHO to date. We suggest that there is a considerable amount of physical information about the solar
coronal plasma that can be readily gleamed from the BP detection database. In this paper we discuss only a small portion of
the possible correlations, but we point to the possibility of BP lifetime distributions that are well described by modified
power-laws; the components of which vary with the different temperature filters and with time over the present solar cycle.
Dedicated to the memory of John (Ian) Hamilton (1938–2004). 相似文献
20.
We compare the shape and position of some plasma formations visible in the polar corona with the cyclic evolution of the global
magnetic field. The first type of object is polar crown prominences. A two-fold decrease of the height of polar crown prominences
was found during their poleward migration from the middle latitudes to the poles before a polar magnetic field reversal. The
effect could be assigned to a decrease of the magnetic field scale. The second type of object is the polar plumes, ray like
structures that follow magnetic field lines. Tangents to polar ray structures are usually crossed near some point, “a magnetic
focus,” below the surface. The distance q between the focus and the center of the solar disk changes from the maximum value about 0.65 R
⊙ at solar minimum activity to the minimum value about 0.45 R
⊙ at solar maximum. At first glance this behaviour seems to be contrary to the dynamics of spherical harmonics of the global
magnetic field throughout a cycle. We believe that the problem could be resolved if one takes into account not only scale
changes in the global magnetic field but also the phase difference in the cyclic variations of large-scale and small-scale
components of the global field. 相似文献