共查询到20条相似文献，搜索用时 31 毫秒
1.
The conditions for accurate electron density diagnostics in the solar transition region are discussed, and result shows that lines from Si?viii can provide an excellent tool for electron density diagnostics of the emitting plasma. For the Si?viii 1440.50 Å and 1445.75 Å lines, the principle of the electron density diagnostics is discussed for any intensity ratio. By the observed intensity ratio, the diagnostic results of the electron density for the quiet sun and the active region are calculated, and results indicate that in the quiet sun, the averaged electron density is \(\log (N_{e}) = 8.63\); while in the active region, the averaged density gets the maximum \(\log (N_{e}) = 8.86\) in the active region (B), and gets the minimum \(\log (N_{e}) = 8.38\) in the active region (E), where the electron density is in the unit of cm?3. Finally, the relationship of intensity ratio and electron density is discussed, in the case of lower and higher electron density limits. This discussion is significant in the electron density diagnostics, which will be important for study on coronal heating and acceleration of solar wind. 相似文献
2.
A certain class of non-thermal electron distributions can exhibit more mono-energetic shape and a higher peak than the Maxwellian
distribution. This type of electron distribution can be observed mainly in flaring plasmas. We have studied the influence
of this kind of electron energy distribution on the excitation equilibrium of Fe VIII – Fe XVI in the solar corona. The changes
in synthetic spectra of the emission lines belonging to these ions due to this non-thermal distribution are shown. The possibilities
of finding the shape of the energy distribution function of electrons from the Fe line ratios are also discussed. The results
can be used for diagnostics of coronal plasmas where the deviations of particle energy distributions from the Maxwellian one
can be significant. 相似文献
3.
Paul A. Crowther Peter S. Conti 《Monthly notices of the Royal Astronomical Society》2003,343(1):143-163
In solar extreme ultraviolet spectra the He i and He ii resonance lines show unusual behaviour and have anomalously high intensities compared with other transition region lines. The formation of the helium resonance lines is investigated through extensive non-local thermal equilibrium radiative transfer calculations. The model atmospheres of Vernazza, Avrett & Loeser are found to provide reasonable matches to the helium resonance line intensities but significantly overestimate the intensities of other transition region lines. New model atmospheres have been developed from emission measure distributions derived by Macpherson & Jordan, which are consistent with SOHO observations of transition region lines other than those of helium. These models fail to reproduce the observed helium resonance line intensities by significant factors. The possibility that non-Maxwellian electron distributions in the transition region might lead to increased collisional excitation rates in the helium lines is studied. Collisional excitation and ionization rates are recomputed for distribution functions with power-law suprathermal tails that may form by the transport of fast electrons from high-temperature regions. Enhancements of the helium resonance line intensities are found, but many of the predictions of the models regarding line ratios are inconsistent with observations. These results suggest that any such departures from Maxwellian electron distributions are not responsible for the helium resonance line intensities. 相似文献
4.
We investigate the possibility to diagnose the ??-distributions from the EUV spectra observed by the Hinode/EIS spectrometer. Observable lines of the most abundant elements except Fe are considered. Synthetic spectra for the ??-distributions with ??=2??C?10 and the Maxwellian distribution were calculated for a range of temperatures and electron densities. We find that only a small number of O, S, Ca, and Ni line ratios are sensitive to???. A?list of the best diagnostic options using transition region and coronal lines is provided. Usually, the line ratios sensitive to ?? are also sensitive to electron density. Weak O?iv lines are a notable exception. These lines offer greatest sensitivity to ?? from all the lines observed by Hinode/EIS. Density diagnostics using lines of the non-Fe elements is discussed and the influence of ?? on the diagnostics of electron density is presented. The density diagnostics using these non-Fe EIS lines are strongly affected by both known and unknown blends. Therefore, we performed the density diagnostics using the Fe?xii??C?xiv lines. Subsequently, these proposed diagnostic methods for ??-distributions are tested using the spectral atlas obtained by Brown et?al. (Astrophys. J. Suppl. 176, 511, 2008). These data do not provide conclusive evidence for the presence of ??-distributions due to possible plasma multitermality, a low observed signal-to-noise ratio, and unremovable or unknown blends. 相似文献
5.
Electron beams accelerated during solar flares carry electric currents which should be neutralized by so-called return currents.
Both the electron beam and return current modify the electron distribution function in the solar transition region and low
corona. Thus, they influence the intensities of the spectral lines formed in these layers. Synthetic spectra for the solar
flare atmosphere are computed from model conditions and the possibilities of diagnostics of the return current from the EUV
and X-ray line spectra are discussed. 相似文献
6.
F. P. Keenan 《Solar physics》1984,91(1):27-31
Non-Maxwellian collision rates of the Be-sequence ions Ciii and Ov in the solar transition region are derived for quiet Sun and flare conditions using the electron velocity distribution functions of Shoub. The rates are found to be enhanced relative to the Maxwellian values but only at low temperatures where the fractional abundances of these species is very small. This implies that the electron density and temperature diagnostics used by previous authors for the transition region will be unchanged by non-Maxwellian effects. It is noted that such effects will only be important for species that are formed at low temperatures and have large transition energies such as Hei. 相似文献
7.
Elena Dzifčáková 《Solar physics》2000,196(1):113-127
The influence of electron non-Maxwellian distributions (power and -distribution) on the electron excitation rate in the solar corona is demonstrated. It is shown that the deviations in electron excitation rate are sufficient to affect intensities of spectral lines. As an example the diagnostics of a power-law distribution are demonstrated for a simplified calculation of the resonance lines of Fexxiv, Fexxv and Fexxvi. The results can be used in diagnosing solar flare plasmas, where the deviations of the electron distribution from a Maxwellian distribution can be large. 相似文献
8.
The density dependence of solar EUV line intensity ratios from Mg VIII, Si VII, S IX and Si IX ions have been used to determine electron densities in the quiet Sun and coronal holes. The line intensity values have been computed using a model atmosphere of Kopp and Orrall (1976) in order to emphasize the utility of the lines studied which could be compared with observational data that future missions might provide. 相似文献
9.
The excitation equilibrium of Fexxv in the solar corona for electron power distributions is presented. A parametric form of the distribution function is used to demonstrate the changes in the excitation equilibrium due to the shape of the distribution. A pseudo-temperature is used for better understanding of the changes in the excitation equilibrium. The Fexxv line intensities depend on the shape of the electron distribution and unusual Fe line ratios can be observed for non-thermal distribution. The results can be used in specific applications in the solar corona, especially in diagnostics of the impulsive phase of solar flares, where the deviations from the Maxwellian distribution can be large. 相似文献
10.
New calculations for Si vii/Mg vii and Si ix/Mg ix theoretical line ratios as a tool for plasma density diagnostics and for the estimation of relative element abundance in the solar atmosphere are presented, making use of the EUV spectrum of an active region obtained by the Solar EUV Rocket Telescope and Spectrograph (SERTS). Theoretical line ratios, hitherto not observed, are discussed for diagnosing solar plasma from the observations obtainable with the Coronal Diagnostic Spectrometer (CDS) instrument on board the SOHO mission.In the honour of Dr P. K. Raju, Indian Institute of Astrophysics, Bangalore, on the completion of his 60 years. 相似文献
11.
J. G. Doyle 《Solar physics》1983,89(1):115-131
A wavelength list is presented for the solar flare of 7 September, 1973 in the spectral range 1335 Å–380 Å. The ions observed suggest a range of temperatures in the flare plasma from 8 × 103 K to 107 K. This wavelength range contains many of the important electron density diagnostics lines for the solar transition zone and corona. The line list should also be of potential use in the identification and comparison with stellar spectra. 相似文献
12.
Suresh Chandra 《Astrophysics and Space Science》1983,92(1):223-227
The situation that a forbidden line is produced from a metastable level, and is optically thin is used for calculating the upper limit of the electron density so that the line is observable. These upper limits for various lines may give the idea about the electron density in the emitting region of the solar corona and the transition region. 相似文献
13.
Line intensity ratios of EUV emission lines from Navii and Alix have been considered for electron density and temperature determinations within the chromosphere-corona transition region and the corona. The electron pressure within the emission region has been assumed to be a constant parameter. Theoretical line intensities for these ions have been computed using a model solar atmosphere and compared with the values as observed by ATM ultraviolet spectrometer. The observed intensities correspond to the average quiet-Sun conditions near solar minimum. 相似文献
14.
B. N. Dwivedi 《Solar physics》1996,165(2):399-402
We present new calculations for Si VII line ratio density diagnostics and suggest some observable lines, hitherto not observed, for observations to be obtained with the Coronal Diagnostic Spectrometer (CDS) on board the SOHO mission. 相似文献
15.
EUV bi-directional jets are a prominent class of phenomena characterizing the solar transition region. Using simultaneously obtained SUMER observations in the chromospheric Si ii 1251.16 Å and C i 1251.17 Å, transition region N v 1238.8 Å and coronal Mg x 625 Å lines we show an example of a bi-directional jet observed in the chromospheric and the transition region lines but not showing any detectable signature in the coronal line. The phenomenon, however, was also clearly detected by the TRACE imager with the 171 Å filter. This discrepancy is explained here with a non-Maxwellian electron distribution which makes a significant fraction of the plasma in the TRACE 171 Å pass-band to be derived from temperatures around ≈ 300 000 K, as opposed to ≈ 800 000 K. This could have implications for other phenomena observed in the TRACE pass-bands, including the transition region ‘moss’ and the 3- and 5-min oscillations. 相似文献
16.
The EUV lines suitable to diagnose possible κ-distributions in the solar corona are examined. A set of synthetic spectra for various values of the κ-parameter, characterizing the non-thermal κ-distributions, electron densities, and the mean energy of the distributions are calculated in the spectral range corresponding to the Hinode/EIS and Coronas-F/SPIRIT detectors. The strong EUV lines of Fe in various degrees of ionization are used to analyze the sensitivity of the line ratios to the shape of the distribution function, electron density, and temperature or the parameter T of the κ-distribution. The EUV lines suitable for the diagnostics of the distribution function are proposed and the conditions for their usage are discussed. 相似文献
17.
J. Lang D.H. Brooks M.G. O'Mullane C.D. Pike H.P. Summers W.T. Thompson 《Solar physics》2001,201(1):37-55
New measurements of line intensity ratios in the Be-like ion Si xi are presented for observations of the quiet Sun, active regions, coronal holes and above-limb regions obtained using the Coronal Diagnostic Spectrometer on the Solar and Heliospheric Observatory. A model ion, constructed using the best available atomic data, is used to predict the line intensity ratios for a wide range of electron temperatures and densities. Comparisons of the theoretical ratios with the new intensity ratios as well as with those from previous solar observations and laboratory measurements are given. The usefulness of the ratios for electron temperature and density diagnostics, as well as for spectrometer calibration, is discussed. 相似文献
18.
In space plasmas, particle distributions are often observed having high energy tails and are well fitted by kappa distribution function. However, in auroral region electrons are expected to be accelerated mainly along the magnetic field lines and one may expect Maxwellian behaviour in perpendicular direction. Therefore, in the present study propagation characteristics of electromagnetic electron cyclotron (EMEC) waves is studied by employing kappa-Maxwellian distribution function for energetic trapped electrons in auroral region. Real frequency and the growth rate expressions have been solved numerically for kappa-Maxwellian plasma and then analyzed by considering the effect of different plasma parameters for wide range of auroral altitudes. The numerical results obtained show that growth rate increases with the increase in ratio \({\omega_{pe}} / {\varOmega_{e}}\), plasma beta, temperature anisotropy \({T_{\bot}} / {T_{\parallel}}\) and trapped electron drift speed but decreases when superthermal electron population increases. 相似文献
19.
Existence and characteristics of ion-acoustic (IA) wave modulation are studied in a plasma with two-temperature electron satisfying kappa distribution. Based on the multiple time scales perturbation, a nonlinear Schrödinger equation (NLS) is derived. Similar to the case of double Maxwellian electrons, both polarities of envelope soliton can exist over restricted ranges of the fractional hot electron density ratio and two-temperature superthermal electrons. The transition from stable dark solitons to unstable bright ones shifts to the smaller wavelength regions in the presence of cool and hot superthermal electrons. It is shown that the small values of the hot electron populations leads to shrinking the modulation instability region. It is also found the instability growth rate reduces due to the presence of hot electrons. The result of present investigation contributes to the physics of wave modulation in Saturn’s magnetosphere where two-temperature electrons with kappa distribution exist. 相似文献
20.
K.J.H. Phillips M. Mathioudakis D.P. Huenemoerder D.R. Williams M.E. Phillips F.P. Keenan 《Monthly notices of the Royal Astronomical Society》2001,325(4):1500-1510
The primary objective of this work is the analysis and interpretation of coronal observations of Capella obtained in 1999 September with the High Energy Transmission Grating Spectrometer on the Chandra X-ray Observatory and the Extreme Ultraviolet Explorer ( EUVE ). He-like lines of O (O vii ) are used to derive a density of 1.7×1010 cm−3 for the coronae of the binary, consistent with the upper limits derived from Fe xxi , Ne ix and Mg xi line ratios. Previous estimates of the electron density based on Fe xxi should be considered as upper limits. We construct emission measure distributions and compare the theoretical and observed spectra to conclude that the coronal material has a temperature distribution that peaks around 4–6 MK , implying that the coronae of Capella were significantly cooler than in the previous years. In addition, we present an extended line list with over 100 features in the 5–24 Å wavelength range, and find that the X-ray spectrum is very similar to that of a solar flare observed with SMM . The observed to theoretical Fe xvii 15.012-Å line intensity reveals that opacity has no significant effect on the line flux. We derive an upper limit to the optical depth, which we combine with the electron density to derive an upper limit of 3000 km for the size of the Fe xvii emitting region. In the same context, we use the Si iv transition region lines of Capella from HST /Goddard High-Resolution Spectrometer observations to show that opacity can be significant at T =105 K , and derive a path-length of ≈75 km for the transition region. Both the coronal and transition region observations are consistent with very small emitting regions, which could be explained by small loops over the stellar surfaces. 相似文献