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1.
Simple considerations of observed variation with wavelength of polarization on the solar disc, computed continuum polarization, and estimated line polarization have led to the following simple conclusions (more qualitative than quantitative); (a) The metal abundances in the photosphere are five times larger than the classical values adopted in the BCA model of the solar photosphere. (b) The depolarization factor k in lines is an increasing function of wavelength. (c) Assuming that k varies as 2, an additional polarization (which can be either solar or instrumental) has to be taken into account.  相似文献   

2.
FIRSTOVA  N. M.  HÉNOUX  J.-C.  KAZANTSEV  S. A.  BULATOV  A. V. 《Solar physics》1997,171(1):123-144
Measurements of linear polarization in hydrogen H and H lines, made with the Large Solar Vacuum Telescope of Baikal Astrophysical Observatory and Automated Solar Telescope of Sayan Solar Observatory, affiliated with the Russian Institute of Solar and Terrestrial Physics, are reported in this paper. Short-term polarization associated with solar flares is found to be present in active regions. There is a significant tendency for the H polarization vector to be radial, i.e., in the flare-to-disk-center direction. This polarization may be due to atmospheric bombardment by hecta keV protons. On the other hand, the polarization vector is found to be perpendicular to the radial direction at some locations where the line profile has a typical mustache shape suggesting a bombardment by energetic electrons. The H line is also linearly polarized. However, no preferential direction of polarization is found in this line, which is formed more deeply in the solar atmosphere.  相似文献   

3.
An instrument designed to record polarization in the region 120–150 nm of the solar spectrum was launched on the satellite Intercosmos-16, July 27, 1976. The aim was to search for resonance-line polarization that is caused by coherent scattering. Oblique reflections at gold- and aluminium-coated mirrors in the instrument were used to analyze the polarization. The average polarization of the L solar limb was found to be less than 1%. It is indicated how future improved VUV polarization measurements may be a diagnostic tool for chromospheric and coronal magnetic fields and for the three-dimensional geometry of the emitting structures.On leave from Lund Observatory, S-22224 Lund, Sweden.The National Center for Atmospheric Research is sponsored by the National Science Foundation.  相似文献   

4.
Summary The physics of impact polarization is briefly reviewed in this paper. Methods for derivating the impact spectropolarimetric parameters relevant for the formation of H linear polarization are summarized. Spectropolarimetric techniques can provide information on the velocity distribution function of energetic particles. Since the most advanced application of this technique to astrophysics is in solar flare physics, recent results achieved by its application to particles accelerated in solar flares are presented.  相似文献   

5.
Hanaoka  Y. 《Solar physics》2004,222(2):265-278
We developed a polarimeter with ferroelectric liquid crystals (FLCs) to observe polarization of flare kernels in the H line. Polarization is one of the important diagnostics of the high-energy particles in solar flares, and high-cadence imaging polarimetry with the precision of the order of 0.1% is required to observe the polarization of flare kernels. However, to achieve such high precision is difficult mainly due to the seeing-induced polarization error, which particularly appears around the flare kernels, because the brightness gradient is steep there. To reduce the seeing-induced error, a high modulation frequency is required, and our new polarimeter based on the combination of a high-speed CCD camera and FLCs realized high-frequency polarization modulation nearly 250 Hz. We evaluated the polarization error, and confirmed that the error was significantly reduced with the new polarimeter. We concluded that the polarimeter with FLCs meets the requirement of solar flare polarimetry.  相似文献   

6.
The polarization structure in several spectral lines in solar type stars is computed using the method described by McKenna (1981, 1984a). The frequency redistribution function used for these calculations is a linear combination ofR II andR III. The line profiles and polarization structures have been computed for several weak solar resonance lines includingKi 7664 Å, Sri 4607 Å, Baii 4554 Å, for various polar angles along the stellar disk. Both the line profiles and polarization structures as well as the center to limb behavior of the line center polarization agree well with observations.The somewhat stronger resonance line Cai 4227 Å shows a different polarization structure when compared to the weaker solar resonance lines. It is found that for strong resonance lines the proper redistribution function to be used is a linear combination ofR III andR v (see McKenna, 1981, 1984b; Heinzel, 1981). The major reason for this is that for strong resonance lines both the upper and lower levels are broadened by collisions. This violates the assumptions upon which the redistribution functionsR II andR III are based.  相似文献   

7.
Stenflo  J. O. 《Solar physics》1974,37(1):31-42
The resonance polarization in Ca i 4226.73 has been measured close to the solar limb for three values of = cos. The polarization has maxima in the wings at about –500 and + 400 mÅ from the line center, the plane of polarization (electric vector) being parallel to the solar limb. The blue wing is more polarized than the red wing, contrary to earlier results of Brückner (1963). Local minima in the polarization curves occur at the position of blends. The polarization in the wings increases rapidly with decreasing . At = 0.15 the maximum polarization in the blue wing is about 2.4%.The observations are in good qualitative agreement with the recent theory of Dumont et al. (1973), but the observed polarization degrees are significantly smaller than the computed values. This may be explained by the inadequate formula for van der Waals broadening used in the theoretical calculations. Much of the discrepancies between observed and computed values disappear if the recent value of Lites (1974) for the collisional damping constant is used. Further improvements in theory and observation are discussed.  相似文献   

8.
The polarization of hard solar X-radiation (> 10 keV) is calculated on the assumption that electrons get a non-isotropic velocity distribution in the initial phase of a flare. The brems-strahlung generated by nonthermal electrons spiralling around magnetic field lines with discrete pitch angles is considerably polarized if observed at approximately right angles to the magnetic field. In the energy range from 10 to 50 keV the degree of polarization is not strongly dependent on the photon energy. For pitch-angle distributions of the form sin2 and cos2, the polarization has opposite signs; it decreases appreciably at high photon energies. The observation of X-ray polarization will be useful in deducing the physical conditions in flares.  相似文献   

9.
We have recently built and tested an instrument designed to measure the polarization of the hard (5–30 keV) X-ray emission from solar flares, and thereby to investigate the energy release mechanism and constrain flare models. In particular, these measurements will help to determine whether hard X-ray bursts are produced by nonthermal or by thermal electrons. The polarimeter makes use of the angular dependence of Thomson scattering from targets of metallic lithium. It has an energy resolution of a few keV, a time resolution of 5 s, and sufficient sensitivity to measure polarization levels (3) of a few percent in about 10 s for a moderate strength solar flare. The instrumental polarization has been directly measured and found to be within the design goal of 1%. This polarimeter is scheduled to be flown as part of the OSS-1 pallet on an early Space Shuttle mission.  相似文献   

10.
We describe an instrument we have built and installed at Mees Solar Observatory on Haleakala, Maui, to measure polarization in narrow-band solar images. Observations in Zeemansensitive photospheric lines have been made for nearly all solar active regions since the instrument began operations in 1992. The magnetograph includes a 28-cm aperture telescope, a polarization modulator, a tunable Fabry-Pérot filter, CCD cameras and control electronics. Stokes spectra of a photospheric line are obtained with 7 pm spectral resolution, 1 arc sec spatial resolution over a field 4.7 arc min square, and polarimetric precision of 0.1%. A complete vector magnetogram observation can be made every eight minutes. The flexibility of the instrument encourages diverse observations: besides active region magnetograms we have made, for example, composite vector magnetograms of the full solar disk, and H polarization movies of flaring regions.  相似文献   

11.
Starting from the idea that the electrons accelerated during a solar flare have originally a preferred direction, the angular distribution and the polarization of bremsstrahlung below 10 Å is calculated taking into account the influence of the magnetic field. The energy distribution of the nonthermal electrons is based on X-ray spectra measured by the Leicester group during flares in 1962 and 1967. In addition to the case of a fixed angle between the electron velocity and the magnetic field, an angular distribution of the form sin n is considered. The results may be used to test flare models. Recent measurements of the polarization of solar X-radiation yield the expected order of magnitude.Paper presented to the Int. Symp. on Solar-Terr. Phys., Leningrad, May 1970.  相似文献   

12.
A strong S-component of solar radiation was identified during the total solar eclipse of November 12, 1966. Its characteristics, as measured at 4.28 cm, were studied in terms of flux and polarization, and its spectral features were derived by the use of data from other observatories. The whole source presented approximately the typical characteristics suggested by some authors in the last few years, and further it has been shown that it could be resolved into at least two enhanced regions, one showing unpolarized radiation with a brightness temperature T b 1.2 × 106 °K, and the other showing 50% of left-handed circularly polarized radiation, with T b 0.7 × 106 °K. The source's overall characteristics favour the presence of non-thermal absorption at the emitting regions.  相似文献   

13.
The linear polarization of X-ray lines from highly charged hydrogenic ions is calculated under the assumption that the ions are collisionally excited by nonthermal electrons with an anisotropic pitch-angle distribution around magnetic field lines. The results are applied to the conditions in solar flares. The maximum degree of polarization to be expected is quite low, of the order of some percent. In case of favourable conditions it should be feasible to detect line polarization during flares if the short-wavelength fine-structure component of the L doublet is observed.  相似文献   

14.
The Chromospheric Lyman-Alpha SpectroPolarimeter is a sounding rocket instrument designed to measure for the first time the linear polarization of the hydrogen Lyman-\({\upalpha }\) line (121.6 nm). The instrument was successfully launched on 3 September 2015 and observations were conducted at the solar disc center and close to the limb during the five-minutes flight. In this article, the disc center observations are used to provide an in-flight calibration of the instrument spurious polarization. The derived in-flight spurious polarization is consistent with the spurious polarization levels determined during the pre-flight calibration and a statistical analysis of the polarization fluctuations from solar origin is conducted to ensure a 0.014% precision on the spurious polarization. The combination of the pre-flight and the in-flight polarization calibrations provides a complete picture of the instrument response matrix, and a proper error transfer method is used to confirm the achieved polarization accuracy. As a result, the unprecedented 0.1% polarization accuracy of the instrument in the vacuum ultraviolet is ensured by the polarization calibration.  相似文献   

15.
The Oppenheimer-Penny theory, as developed by Percival and Seaton (1958), is applied to calculate the polarization of L radiations from hydrogen-like ions when the impact electrons are distributed such that their probability is more in the regions close to the magnetic field. The degrees of polarization are averaged over the energy of non-thermal electrons generated during the initial phase of solar flares. It is found that the degrees of polarization do not depend on the atomic number of the ion.  相似文献   

16.
A synoptic study of the occurrence and polarization of 160 MHz noise storms recorded at Culgoora during the current solar cycle shows that the storm sources occur in large unipolar cells extending >90° in solar longitude and 60° in latitude, with lifetimes of 1 yr. From solar maximum onwards these large cells stretch across the solar equator to form a longitudinal sector pattern reminiscent of that observed in the interplanetary magnetic field. Comparisons with published heliospheric current sheet simulations support this conclusion. The noise storms occur in the strong magnetic fields above large, complex, flare-active sunspots. Unlike most active regions, those associated with noise storms do not always have dominant sunspots as leaders. Rather, about one-third have the dominant sunspot as a follower. The dominant sunspot polarities tend to agree with the long-lived sector structure, implying that emerging magnetic flux occurs at preferred longtitudes on the solar surface.  相似文献   

17.
The circular polarization of complex solar bursts was measured at short microwaves (22 GHz, × 1.35 cm) with high sensitivity (0.03 s.f.u. r.m.s.) and high time resolution (5 ms). The polarization shows up as soon as an excess burst emission is measured. Two components are found in the time development of the degree of circular polarization: (1) a steady level, sometime changing smoothly with time; (2) superimposed faster polarization time structures, small compared to the basic steady degree of polarization, and often not clearly related to the burst flux time structures. The observed degrees may range from 10% to more than 85%.In memoriam (1942–1981).  相似文献   

18.
The expected polarization of the sodium D lines from solar prominences is computed as a function of the local magnetic field vector. To this aim, the formulation of the Hanle effect in terms of the statistical tensors developed by Landi Degl'Innocenti (1982) is employed, with minor changes connected to hyperfine structure. The sodium atoms are described in the incomplete Paschen-Back regime so that the validity of the results is not limited to weak magnetic fields. The polarization diagrams obtained are discussed and compared with the corresponding diagrams for the helium D3 line.  相似文献   

19.
A broadband spectrometer for decimeter and microwave radio bursts   总被引：5，自引：0，他引：5  
Observations of solar microwave bursts with high temporal and spectral resolution have shown interesting fine structures (FSs) of short duration and small bandwidth which are usually superimposed on the smooth continuum. These FSs are very intense (up to 1015 K) and show sometimes a high degree of circular polarization (up to 100%). They are believed to be generated by electron cyclotron maser emission (ECME) in magnetic loops. Another type are the microwave type III bursts, which are drifting microwave FSs, and are probably the signatures of travelling electron beams in the solar atmosphere. The exact emission mechanisms for these phenomena, in particular the source configuration, the plasma parameters and the distribution of radiating electrons are not clear. For a detailed study of these problems new observations of intensity and polarization with high resolution in time and in frequency in decimeter and microwave wavebands are essential. In order to investigate these features in greater detail, spectrometers with high temporal and spectral resolution are being developed by the solar radio astronomy community of China (Beijing Astronomical Observatory (BAO), Purple Mountain Observatory (PMO), Yunnan Astronomical Observatory (YAO), and Nanjing University (NJU)). The frequency range from 0.7 to about 12 GHz is covered by about five spectrometers in frequency ranges of 0.7–1.4 GHz, 1–2 GHz, 2.4–3.6 GHz, 4.9–7.3 GHz, and 8–12 GHz, respectively. The radiospectrometers will form a combined type of swept-frequency and multi-channel receivers. The main characteristics of the solar radio spectrometers are: frequency resolution: 1–10 MHz; temporal resolution: 1–10 ms; sensitivity: better than 2% of the quiet-Sun level. We pay special attention to the sensitivity and the accuracy of polarization. Now, the 1–2 GHz radiospectrometer is being set up. The full system will be set up in 3–4 years.Presented at the CESRA-Workshop on Coronal Magnetic Release at Caputh near Potsdam in May 1994.  相似文献   

20.
Results are presented from spectro-imaging polarimetry of radiation from the local solar corona during the 2013 total solar eclipse in Gabon. This polarimetric observation was performed from 516.3 nm to 532.6 nm using a prototype Fiber Arrayed Solar Optical Telescope (FASOT). A polarimetric noise level on the order of \(10^{-3}\) results from a reduced polarimetric optical switching demodulation (RPOSD) procedure for data reduction. It is revealed that the modality of fractional linear polarization profiles of the green coronal line shows a diversity, which may indicate complex mechanisms. The polarization degree can approach 3.2 % above the continuum polarization level on a scale of 1500 km, and the nonuniform spatial distribution in amplitude and polarization direction is found even within a small field of view of 7500 km. All of this implies that the coronal polarization is highly structured and complex even on a small scale.  相似文献   

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