共查询到20条相似文献，搜索用时 31 毫秒
1.
R. Kano T. Sakao H. Hara S. Tsuneta K. Matsuzaki K. Kumagai M. Shimojo K. Minesugi K. Shibasaki E. E. DeLuca L. Golub J. Bookbinder D. Caldwell P. Cheimets J. Cirtain E. Dennis T. Kent M. Weber 《Solar physics》2008,249(2):263-279
The X-ray Telescope (XRT) aboard the Hinode satellite is a grazing incidence X-ray imager equipped with a 2048×2048 CCD. The XRT has 1 arcsec pixels with a wide field
of view of 34×34 arcmin. It is sensitive to plasmas with a wide temperature range from < 1 to 30 MK, allowing us to obtain
TRACE-like low-temperature images as well as Yohkoh/SXT-like high-temperature images. The spacecraft Mission Data Processor (MDP) controls the XRT through sequence tables with
versatile autonomous functions such as exposure control, region-of-interest tracking, flare detection, and flare location
identification. Data are compressed either with DPCM or JPEG, depending on the purpose. This results in higher cadence and/or
wider field of view for a given telemetry bandwidth. With a focus adjust mechanism, a higher resolution of Gaussian focus
may be available on-axis. This paper follows the first instrument paper for the XRT (Golub et al., Solar Phys.
243, 63, 2007) and discusses the design and measured performance of the X-ray CCD camera for the XRT and its control system with the MDP. 相似文献
2.
The flattening at the low energy end of the hard X-ray (HXR) photon spectrum of solar flares was generally thought to be due to a cutoff of nonthermal electrons in flares. However, some authors have suggested that inverse Compton scattering (i.e., the albedo effect) or certain other reaction of flare photons with the lower atmosphere can also lead to the flattening. This paper adopts the method of deriving the cutoff proposed by Gan et al. [12–14], and makes a statistical analysis on 100 flares observed by the satellite Ramaty High Energy Solar Spectroscopy Imager (RHESSI) in 2002–2005. We found that after the albedo correction, the HXR photon spectra of 18 flares can be fitted with single powerlaw spectra, and those of 80 flares, with double power-law spectra. Besides, 21 flares can be directly interpreted with a single power-law electron spectrum plus a low energy cutoff. The range of the low energy cutoff is 20–50 keV and the mean value is approximately 30 keV. Some other possible interpretations are also investigated. 相似文献
3.
A number of independent arguments indicate that the toroidal flux system responsible for the sunspot cycle is stored at the
base of the convection zone in the form of flux tubes with field strength close to 105 G. Although the evidence for such strong fields is quite compelling, how such field strength can be reached is still a topic
of debate. Flux expulsion by convection should lead to about the equipartition field strength, but the magnetic energy density
of a 105-G field is two orders of magnitude larger than the mean kinetic energy density of convective motions. Line stretching by
differential rotation (i.e., the “Ω effect” in the classical mean-field dynamo approach) probably plays an important role, but arguments based on energy considerations show that it does not seem feasible
that a 105-G field can be produced in this way. An alternative scenario for the intensification of the toroidal flux system in the overshoot
layer is related to the explosion of rising, buoyantly unstable magnetic flux tubes, which opens a complementary mechanism for magnetic-field intensification.
A parallelism is pointed out with the mechanism of “convective collapse” for the intensification of photospheric magnetic
flux tubes up to field strengths well above equipartition; both mechanisms, which are fundamentally thermal processes, are
reviewed. 相似文献
4.
The acceleration of charged particles in the solar corona during flares is investigated in terms of a model in which the electrons and ions preaccelerated in the magnetic reconnection region are injected into a collapsing magnetic trap. Here, the particle energy increases rapidly simultaneously through the Fermi and betatron mechanisms. Comparison of the efficiencies of the two mechanisms shows that the accelerated electrons in such a trap produce more intense hard X-ray (HXR) bursts than those in a trap where only the Fermi acceleration mechanism would be at work. This effect explains the Yohkoh and RHESSI satellite observations in which HXR sources more intense than the HXR emission from the chromosphere were detected in the corona. 相似文献
5.
We investigate the damping of longitudinal (i.e., slow or acoustic) waves in nonisothermal, hot (T≥ 5.0 MK), gravitationally stratified coronal loops. Motivated by SOHO/SUMER and Yohkoh/SXT observations, and by taking into account a range of dissipative mechanisms such as thermal conduction, compressive viscosity, radiative cooling, and heating, the nonlinear governing equations of one-dimensional hydrodynamics are solved numerically for standing-wave oscillations along a magnetic field line. A semicircular shape is chosen to represent the geometry of the coronal loop. It was found that the decay time of standing waves decreases with the increase of the initial temperature, and the periods of oscillations are affected by the different initial footpoint temperatures and loop lengths studied by the numerical experiments. In general, the period of oscillation of standing waves increases and the damping time decreases when the parameter that characterises the temperature at the apex of the loop increases for a fixed footpoint temperature and loop length. A relatively simple second-order scaling polynomial between the damping time and the parameter determining the apex temperature is found. This scaling relation is proposed to be tested observationally. Because of the lack of a larger, statistically relevant number of observational studies of the damping of longitudinal (slow) standing oscillations, it can only be concluded that the numerically predicted decay times are well within the range of values inferred from Doppler shifts observed by SUMER in hot coronal loops. 相似文献
6.
Using numerical simulations, we evaluated the gate structure effect of the front-illuminated (FI) charge-coupled device (CCD) on determining the point spread function (PSF) from the analysis of undersampled experimental data. The PSF of the Soft X-ray Telescope onboard Yohkoh was studied as a model case. Its full-width at half-maximum is about one pixel size, and the FI CCD was equipped in the telescope as a detector. Of the three emission lines used during the pre-launch experiment, the data from the lowest-energy line (carbon K-line, 0.28 keV) were significantly influenced by the gate structure. The results from previous studies regarding the analysis of pre-launch data were examined and compared with the results from our simulation, and the expected error ranges of the gate structure effect are discussed. We found that the error caused by the effect of the gate structure is significant; at an energy of 0.28 keV, the error may lead to a too sharp PSF by about a few tens of percent. 相似文献
7.
The European Photon Imaging Camera(EPIC), is the X-ray imaging and medium spectroscopy instrument for theESA X-ray Multi Mirror telescope(XMM) mission. TheCCD detectors to be used in the three focal plane cameras will provide images in the energy band from 0.1 to 10 keV. However, spectral studies may be compromised by low energy, optical photon contamination. In order to reduce this effect, a number of filters will be incorporated onto a rotating mechanism in the camera head. The filters will be chosen to provide a significant reduction in the optical contamination from a source whilst minimising the attenuation of the X-ray flux. Four commercial filters are described here and their effects on calculated typical source fluxes evaluated. In addition, two alternative filter designs are described and their effects on a simulated source spectra are debated. In both cases, particular attention is given to the problem of maintaining high sensitivity at soft X-ray energies (less than 2 keV). 相似文献
8.
P. Pant 《Journal of Astrophysics and Astronomy》2006,27(2-3):293-297
The solar observational facilities at ARIES (erstwhile U.P. State Observatory, UPSO), Nainital, began in the sixties with
the acquisition of two moderate sized (25 cm, f/66 off-axis Skew Cassegrain and 15 cm, f/15 refractor) telescopes. Both these
systems receive sunlight through a 45 cm and 25 cm coelostat respectively. The backend instruments to these systems comprised
of a single pass grating spectrograph for spectroscopic study of the Sun and a Bernhard-HalleHα filter, coupled with a Robot recorder camera for solar patrolling inHα respectively. With the advancement in solar observing techniques with high temporal and spatial resolution inHα and other wavelengths, it became inevitable to acquire sophisticated instrumentation for data acquisition. In view of that,
the above facilities were upgraded, owing to which the conventional photographic techniques were replaced by the CCD camera
systems attached with two 15 cm, f/15 Coude refractor telescopes. These CCD systems include the Peltier cooled CCD camera
and photometrics PXL high speed modular CCD camera which provide high temporal and spatial resolution of ∼ 25 ms and ∼ 1.3
arcsec respectively. 相似文献
9.
Guangli Huang 《Solar physics》2009,257(2):323-334
The low-cutoff energy has a strong effect on the relationship between the radiation and electron spectral indices in both
nonthermal gyrosynchrotron and bremsstrahlung theories. Hence, we have to calculate or fit the low-cutoff energy together
with the electron spectral index as two independent parameters. Theoretical calculations of nonthermal gyrosynchrotron and
bremsstrahlung radiations suggest a new method to obtain the exact solutions of the low-cutoff energy and the electron spectral
index from the observable photon spectral indices at two adjacent energy or frequency bands (double power law). One flare
on 10 June 2000 was studied as an example of the hard X-ray and microwave diagnostics for the low-cutoff energy and the electron
spectral index. The results showed some differences between hard X-ray and microwave diagnostics. 相似文献
10.
The point spread function of the SXT telescope aboardYohkoh has been measured in flight configuration in three different X-ray lines at White Sands Missile Range. We have fitted these data with an elliptical generalization of the Moffat function. Our fitting method consists of 2 minimizationin Fourier space, especially designed for matching of sharply peaked functions. We find excellent fits with a reduced 2 of order unity or less for single exposure point spread functions over most of the CCD. Near the edges of the CCD the fits are less accurate due to vignetting. From fitting results with summation of multiple exposures we find a systematic error in the fitting function of the order of 3% near the peak of the point spread function, which is close to the photon noise for typical SXT images in orbit. We find that the full width to half maximum and fitting parameters vary significantly with CCD location. However, we also find that point spread functions measured at the same location are consistent to one another within the limit determined by photon noise. A best analytical fit to the PSF as function of position on the CCD is derived for use in SXT image enhancement routines. As an aside result we have found that SXT can determine the location of point sources to about a quarter of a 2.54 arc sec pixel.This paper is dedicated to the memory of our friend and colleague Kermit Smith, who died in June 1993, after a valient fight with leukemia. 相似文献
11.
EIT waves are observed in EUV as bright fronts. Some of these bright fronts propagate across the solar disk. EIT waves are
all associated with a flare and a CME and are commonly interpreted as fast-mode magnetosonic waves. Propagating EIT waves
could also be the direct signature of the gradual opening of magnetic field lines during a CME. We quantitatively addressed
this alternative interpretation. Using two independent 3D MHD codes, we performed nondimensional numerical simulations of
a slowly rotating magnetic bipole, which progressively result in the formation of a twisted magnetic flux tube and its fast
expansion, as during a CME. We analyse the origins, the development, and the observability in EUV of the narrow electric currents
sheets that appear in the simulations. Both codes give similar results, which we confront with two well-known SOHO/EIT observations
of propagating EIT waves (7 April and 12 May 1997), by scaling the vertical magnetic field components of the simulated bipole
to the line of sight magnetic field observed by SOHO/MDI and the sign of helicity to the orientation of the soft X-ray sigmoids
observed by Yohkoh/SXT. A large-scale and narrow current shell appears around the twisted flux tube in the dynamic phase of its expansion. This
current shell is formed by the return currents of the system, which separate the twisted flux tube from the surrounding fields.
It intensifies as the flux tube accelerates and it is co-spatial with weak plasma compression. The current density integrated
over the altitude has the shape of an ellipse, which expands and rotates when viewed from above, reproducing the generic properties
of propagating EIT waves. The timing, orientation, and location of bright and faint patches observed in the two EIT waves
are remarkably well reproduced. We conjecture that propagating EIT waves are the observational signature of Joule heating
in electric current shells, which separate expanding flux tubes from their surrounding fields during CMEs or plasma compression
inside this current shell. We also conjecture that the bright edges of halo CMEs show the plasma compression in these current
shells. 相似文献
12.
R. Mewe 《Astronomy and Astrophysics Review》1991,3(2):127-168
Summary From the early discovery in 1948 of X-rays from the Solar corona, X-ray spectroscopy has proven to be an invaluable tool in studying hot astrophysical and laboratory plasmas. Because the emission line spectra and continua from optically thin plasmas are fairly well known, high-resolution X-ray spectroscopy has its most obvious application in the measurement of optically thin sources such as the coronae of stars. In particular X-ray observations with theEINSTEIN observatory have demonstrated that soft X-ray emitting coronae are a common feature among stars on the cool side of the Hertzsprung-Russell diagram, with the probable exception of single very cool giant and supergiant stars and A-type dwarfs. Observations with the spectrometers aboardEINSTEIN andEXOSAT have shown that data of even modest spectral resolution (/ = 10–100) permit the identification of coronal material at different temperatures whose existence may relate to a range of possible magnetic loop structures in the hot outer atmospheres of these stars. The higher spectral resolution of the next generation of spectrometers aboard NASA'sAXAF and ESA'sXMM will allow to fully resolve the coronal temperature structure and to enable velocity diagnostics and the determination of coronal densities, from which the loop geometry (i.e. surface filling factors and loop lengths) can be derived. In this paper various diagnostic techniques are reviewed and the spectral results fromEINSTEIN andEXOSAT are discussed. A number of spectral simulations forAXAF andXMM, especially high-resolution iron K-shell, L-shell, and2s-2p spectra in the wavelength regions around 1.9 Å, 10 Å, and 100 Å, respectively, are shown to demonstrate the capabilities for temperature, density, and velocity diagnostics. Finally, iron K-shell spectra are simulated for various types of detectors such as microcalorimeter, Nb-junction, and CCD. 相似文献
13.
The Yohkoh hard X-ray telescope (HXT) observed hard X-rays from the impulsive phase of a long-duration event (LDE) occurring on 14 July
2000. The Yohkoh soft X-ray telescope (SXT) and other instruments observed a large arcade, with width and length ∼30 000 km and ∼120 000 km,
respectively. In hard X-rays, for the first time, a two-ribbon structure was clearly observed in the energy range above 30 keV.
This result suggests that electrons are in fact accelerated in the whole system of this arcade, not merely in a particular
dominant loop. We analyzed the motions of bright kernels in the two hard X-ray ribbons in detail. Assuming these bright kernels
to be footpoints of newly reconnected loops, we infer from their motions that the loops reconnecting early are highly sheared,
while the loops reconnecting later are less sheared. We have also analyzed the hard X-ray spectra of the two ribbons independently.
At the outer edge of a ribbon, the spectrum tends to be harder than that in the inner edge. This suggests that higher-energy
electrons precipitate at the footpoints of outer loops and lower ones do at those of inner loops. We discuss what kind of
model can support this tendency. 相似文献
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17.
The helioseismic instruments aboard the SOHO satellite make it possible to measure solar oscillations as variations of the irradiance (VIRGO) or as variations of the photospheric velocity (GOLF). Theoretically, phase differences between different photometric bands are expected to be around 0 degrees over the p‐mode frequency range. By using VIRGO (red) and VIRGO (blue) data, we find a mean phase shift of 8.05 ± 1.81°, whereas by using VIRGO (green) and VIRGO (blue) data, we got a mean value of –1.04 ± 0.19°. Hence, when the analysis includes the VIRGO infrared range, the Sun's atmosphere does not follow an exact adiabatic behavior. In this study, we use the phase shifts obtained by VIRGO (green) and VIRGO (blue) to determine the non‐adiabatic parameter phase lag (ψT) as a function of frequency. To this aim, we applied the non radial linearized formula put in the complex form by Garrido: we found a mean value of ψT = 179.95°. The lowest value being ψT = 179.90°, the departure from theoretical predictions is less then a tenth of a degree over the entire p mode frequency range. We can state that the solar atmosphere has a behavior close to the adiabatic case, when the phase shifts and amplitude ratios are computed using VIRGO (green) and VIRGO (blue) data. Nevertheless this small deviation is significant. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
18.
Evidence that Synchrotron Emission from Nonthermal Electrons Produces the Increasing Submillimeter Spectral Component in Solar Flares 总被引：1，自引：0，他引：1
Adriana V. R. Silva G. H. Share R. J. Murphy J. E. R. Costa C. G. Giménez de Castro J.-P. Raulin P. Kaufmann 《Solar physics》2007,245(2):311-326
We investigate the origin of the increasing spectra observed at submillimeter wavelengths detected in the flare on 2 November
2003 starting at 17:17 UT. This flare, classified as an X8.3 and 2B event, was simultaneously detected by RHESSI and the Solar
Submillimeter Telescope (SST) at 212 and 405 GHz. Comparison of the time profiles at various wavelengths shows that the submillimeter
emission resembles that of the high-energy X rays observed by RHESSI whereas the microwaves observed by the Owens Valley Solar
Array (OVSA) resemble that of ∼50 keV X rays. Moreover, the centroid position of the submillimeter radiation is seen to originate
within the same flaring loops of the ultraviolet and X-ray sources. Nevertheless, the submillimeter spectra are distinct from
the usual microwave spectra, appearing to be a distinct spectral component with peak frequency in the THz range. Three possibilities
to explain this increasing radio spectra are discussed: (1) gyrosynchrotron radiation from accelerated electrons, (2) bremsstrahlung
from thermal electrons, and (3) gyrosynchrotron emission from the positrons produced by pion or radioactive decay after nuclear
interactions. The latter possibility is ruled out on the grounds that to explain the submillimeter observations requires 3000
to 2×105 more positrons than what is inferred from X-ray and γ-ray observations. It is possible to model the emission as thermal; however, such sources would produce too much flux in the
ultraviolet and soft X-ray wavelengths. Nevertheless we are able to explain both spectral components at microwave and submillimeter
wavelengths by gyrosynchrotron emission from the same population of accelerated electrons that emit hard X rays and γ rays. We find that the same 5×1035 electrons inferred from RHESSI observations are responsible for the compact submillimeter source (0.5 arcsec in radius) in
a region of 4500 G low in the atmosphere, and for the traditional microwave spectral component by a more extended source (50
arcsec) in a 480 G magnetic field located higher up in the loops. The extreme values in magnetic field and source size required
to account for the submillimeter emission can be relaxed if anisotropy and transport of the electrons are taken into account. 相似文献
19.
N2 2P fluorescent intensity was monitored as a function of incident photon energy from 40 to 70 eV. A structure was seen near 52.2 eV. This feature is attributed to the scattering of photoelectrons originating from the N2 2σg molecular orbital with a binding energy of about 37.7 eV. The kinetic energy of these photoelectrons corresponds to the peak of the 2P excitation cross section at 14.5 eV. 相似文献
20.
D. Dravins 《Astronomische Nachrichten》2010,331(5):535-540
High‐fidelity spectroscopy presents challenges for both observations and in designing instruments. High‐resolution and high‐accuracy spectra are required for verifying hydrodynamic stellar atmospheres and for resolving intergalactic absorption‐line structures in quasars. Even with great photon fluxes from large telescopes with matching spectrometers, precise measurements of line profiles and wavelength positions encounter various physical, observational, and instrumental limits. The analysis may be limited by astrophysical and telluric blends, lack of suitable lines, imprecise laboratory wavelengths, or instrumental imperfections. To some extent, such limits can be pushed by forming averages over many similar spectral lines, thus averaging away small random blends and wavelength errors. In situations where theoretical predictions of lineshapes and shifts can be accurately made (e.g., hydrodynamic models of solar‐type stars), the consistency between noisy observations and theoretical predictions may be verified; however this is not feasible for, e.g., the complex of intergalactic metal lines in spectra of distant quasars, where the primary data must come from observations. To more fully resolve lineshapes and interpret wavelength shifts in stars and quasars alike, spectral resolutions on order R = 300 000 or more are required; a level that is becoming (but is not yet) available. A grand challenge remains to design efficient spectrometers with resolutions approaching R = 1 000 000 for the forthcoming generation of extremely large telescopes (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献