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1.
We obtained time-sequence spectroscopic observations in (Fe x) 6374 Å and (Fe xiv) 5303 Å lines successively with the 25-cm coronagraph, and narrow-band and Doppler images in 5303 Å line by the 2-D 10-cm Doppler coronagraph NOGIS at the Norikura Solar Observatory, of a coronal region for about 7 h on 9 19–20, 2001. The raster scans were obtained with a quasi-periodicity of about 14 min and NOGIS obtained the images with an interval of about 1 min. The coronal region observed showed the formation of a coronal loop by a high-speed surge in the 6374 Å line rising from one of the footpoints of the loop. Off the limb spectroscopic observations in the 6374 Å line showed large velocities along the line of sight and vertical to the solar limb at the time of formation of the loop. The 5303 Å line observations showed negligible line-of-sight velocities and low vertical velocities when compared to those in the 6374 Å line. A hump in the intensity plots in 5303 Å with height appears to move up with respect to the solar limb with an average velocity of 4km s–1. The FWHM of the 6374 Å showed a much smaller value of about 0.7 Å near the foot point as compared to a value of 1.2 Å at larger heights at the beginning of observations. Later as the loop developed, the FWHM of 6374 Å line showed a gradual decrease along the loop up to 70 from the limb, reached a minimum value of about 0.5 Å and then increased with height during the formation of the loop; this trend lasted for about 2 h. About 3 h after the beginning of the formation of the loop, the FWHM of 6374 Å emission line showed normal values and normal rate of increase with height with some fluctuations. The FWHM of the 5303 Å line did not show such variations along the loop and showed normal decrease in FWHM with height found earlier (Singh et al., 2003a). These observations suggest that a relatively cooler plasma at a temperature of about 0.7 MK or less (corresponding to minimum value of FWHM of 0.5 Å) was ejected from the transition region with a large velocity of about 48km s–1, heated up in the corona by some process and formed a coronal loop with a height of about 200 above the limb that had lifetime greater than 4 h. It appears that the plasma moved from one of the footpoints and the loop was formed by evaporation of chromospheric plasma. No large-scale brightening and H flare were observed in this region during the observational period of 7 h.On leave from Indian Institute of Astrophysics, Bangalore 560034, India. 相似文献
2.
Fluxes have been computed for Fex (6374 Å) and Fe xiv (5303 Å) lines as a function of solar radii and at various coronal tempratures. The electron density derived from the white light corona during the total solar eclipse of 1980 were used in the computations. Fluxes in adjacent continua have also been computed. The computed ratios of line flux to the square of continuum flux at a coronal temperature of 1.6 × 106 K show a good fit with the observed values for Fex line. Further, radiative excitation seems to dominate over collisional excitation beyond 1.3 solar radius. 相似文献
3.
Brekke P. Kjeldseth-Moe O. Brynildsen N. Maltby P. Haugan S. V. H. Harrison R. A. Thompson W. T. Pike C. D. 《Solar physics》1997,170(1):163-177
EUV spectra obtained with the Coronal Diagnostic Spectrometer (CDS) on the Solar and Heliospheric Observatory (SOHO) show significant flows of plasma in active region loops, both at coronal and transition region temperatures. Wavelength shifts in the coronal lines Mgix 368 Å and Mgx 624 Å corresponding to upflows in the plasma reaching velocities of 50 km s-1 have been observed in an active region. Smaller velocities are detected in the coronal lines Fexvi 360 Å and Sixii 520 Å. Flows reaching 100 km s-1 are observed in spectral lines formed at transition region temperatures, i.e., Ov 629 Å and Oiii 599 Å, demonstrating that both the transition region and the corona are clearly dynamic in nature. Some high velocity events show even higher velocities with line profiles corresponding to a velocity dispersion of 300–400 km s-1. Even in the quiet Sun there are velocity fluctuations of 20 km s-1 in transition region lines. Velocities of the magnitude presented in this paper have never previously been observed in coronal lines except in explosive events and flares. Thus, the preliminary results from the CDS spectrometer promise to put constraints on existing models of the flows and energy balance in the solar atmosphere. The present results are compared to previous attempts to observe flows in the corona. 相似文献
4.
During the total solar eclipse of 11 June, 1983, an imaging dual-channel Fabry-Pérot interferometer was used to obtain line profiles simultaneously in the green 5303 Å [Fe xiv] and the red 6374 Å [Fe x] coronal lines at various positions in the corona. Extensive microdensitometry followed by multi-Gaussian curve-fitting analysis has resulted in the determination of coronal temperatures and velocity separations between different pockets of coronal gas in the line of sight over a large extent of the corona. Fewer high temperature zones are to be found in the corona of 1983 compared with our similar green-line measurements of the solar maximum corona of 1980. The data are consistent with a temperature maximum occurring at 1.2 R
, as found at the 1980 eclipse, but our new data are insufficient to observe farther out than this radius and so determine the position of a maximum. The velocity field in the corona at the 1983 eclipse is less structured compared with that at the 1980 eclipse and is mainly confined to the zone 20–30km s–1. 相似文献
5.
We present theoretical calculations of the observed coronal emission line profiles of Fexiv (5303 Å) and Fex (6374 Å) ions, which are observed at the time of total solar eclipse. Baumbach's relation (Allen, 1973) of electron density has been employed to compute the full width at half maximum FWHM. We have employed several other electron density distributions and found that the calculated differences in the FWHM are within 0.5% of one another. We have used the ion densities N
i/NE given by Jordan (1969). To explain the observed FWHM, we have assumed that the corona is expanding spherically symmetrically with a velocity of one or two mean thermal units and no turbulence is included. With these highly simplified assumptions, we have reproduced qualitatively the profiles and FWHM's of the above lines. However, to explain quantities of FWHM's, we should take into account the inhomogeneities in the structure of the corona. It is thus shown, that turbulence is not necessary to explain the observed FWHM. 相似文献
6.
The purpose of this paper is to report on some intensity measurements of the Fe xiii lines at 10 747 Å and 10 798 Å made during the total eclipse of 12 November, 1966. Infrared spectra were taken of the solar corona at a dispersion of 90 Å per mm, using an RCA image converter and spectrograph aboard the NASA CV 990 aircraft off the coast of southern Brazil. The spectra have been reduced to equivalent width in terms of the coronal continuum and values derived for different points in the corona.The observed equivalent widths of the lines lie in the range 10 to 30 Å for the 10 747 line and 5 to 12 Å for the 10 798 line. The ratio of these equivalent widths is found to vary from 2.3 in the inner corona to 6 at a point 1.36 solar radii from the center of the Sun.The above results are discussed in terms of the excitation mechanisms involved in producing the lines. In particular, the results are compared with the recent theoretical calculations of Chevalier and Lambert, who are the first to include the effects of proton collisions in the excitation of the 3p
2
3
P levels of Fexiii. Our observations are consistent with an electron density of 4 × 108 in the inner corona; a value which compares favorably with those derived by other observers from the strength of the K continuum. These are, to our knowledge, the first eclipse observations of the infrared Fe xiii lines which indicate that proton collisions are important in the excitation of the coronal lines. The coronal abundance of iron is estimated from the equivalent width of the 10 747 line, and in common with other observers we find an overabundance as compared to the photospheric abundance by a factor of 10. 相似文献
7.
Coronal spectra during the total solar eclipse of 1980 February 16, were obtained in the 6374Å [Fex] line using a multislit spectrograph. These spectra have a dispersion of 2.5 Å mm-1. The observed line profiles from 1.1 to 1.7 R⊙ with a spatial resolution of 10 × 22 arcsec2, give half-widths that vary between 0.6 Å and 2.4Å. A large number of locations have half-widths around 1.3 Å corresponding to a temperature of 4.6 × 106 K. If temperature of the order of 1.3 × 106 K are typical of the regions that emit [Fex], then turbulent velocities of ~ 30 km s-1 need to be invoked for the enhanced line broadening. The line-of-sight velocities measured range between +14 km s-1 to -17 km s-1. Most of the locations have velocities less than ±5 km s-1. From these observations we conclude that corona does not show any localized differential mass motion and that it co-rotates with the photospheric layers deeper down. 相似文献
8.
M. Waldmeier 《Solar physics》1970,15(1):167-175
It is well known that in the immediate surroundings of stationary filaments the white light of the corona is strongly reduced. The same effect is observed in the monochromatic emissions of the lines 5303 and 6374 Å, for which in Figures 1–3 some examples are given. This diminuation of light can only be explained by a corresponding diminuation of the density. As the density in the vicinity of the prominence may be as small as one tenth of that of the undisturbed corona, or even smaller in some cases, these features are called cavities. The intensity distribution of the line 5303 Å in the region of a stable prominence observed on October 6, 1969 has been analysed (Figure 4). The cavity turns out to be of the shape of a half-ellipsoid. Its length (in heliographic longitude) was found to be 0.68, its width (in heliographic latitude) 0.20 and its height 0.16 R
(Figure 5). The corresponding dimensions of the enclosed filament are 0.56 (length), 0.10 (width) and 0.08 (height) R
. 相似文献
9.
Penumbral line-core shifts at different heights are determined from the lines Fei 5434.5 Å, Fei 5435.2 Å, and Nii 5435.8 Å using two adjacent water vapor lines for an absolute wavelength scale. The large granular blue shift of 0.6 km s-1 for the faint Fe 5435 line from deep layers yields for the centre-side penumbra absolute velocities up to 3 km s-1. This value is much larger than velocities deduced from the bisectors of the line wings of Ni 5436 and Fe 5434, thus supporting the concern against an interpretation of the line asymmetries in term of a velocity gradient with depth. 相似文献
10.
Spectra around the 6374 Å [Fex] and 7892 Å [Fexi] emission lines were obtained simultaneously with the 25-cm coronagraph at Norikura Observatory covering an area of 200 ×500 of the solar corona. The line width, peak intensity and line-of-sight velocity for both the lines were computed using Gaussian fits to the observed line profiles at each location (4 ×4 ) of the observed coronal region. The line-width measurements show that in steady coronal structures the FWHM of the 6374 Å emission line increases with height above the limb with an average value of 1.02 mÅ arc sec–1. The FWHM of the 7892 Å line also increases with height but at a smaller average value of 0.55 mÅ arc sec–1. These observations agree well with our earlier results obtained from observations of the red, green, and infrared emission lines that variation of the FWHM of the coronal emission lines with height in steady coronal structures depends on plasma temperatures they represent. The FWHM gradient is negative for high-temperature emission lines, positive for relatively low-temperature lines and smaller for emission lines in the intermediate temperature range. Such a behaviour in the variation of the FWHM of coronal emission lines with height above the limb suggests that it may not always be possible to interpret an increase in the FWHM of emission line with height as an increase in the nonthermal velocity, and hence rules out the existence of waves in steady coronal structures. 相似文献
11.
M. Waldmeier 《Solar physics》1975,43(2):351-358
Coronal interferograms in the lines of Fe xiv 5303 Å, He i 5876 Å and Fe x 6374 Å were obtained during the total solar eclipse of 10 July, 1972 (see Figure 2). He i emission was found in the chromosphere only. The upper limit of the D3 equivalent width in terms of the coronal continuous background is 0.013 Å in the inner corona (r=1.15 R⊙). The λ6374 negative was taken with low contrast. The half width of 16374 is 1.0–1.08 Å for a limited area of the corona (P=88?104°, r=1.30?1.44 R⊙). A detailed photometry of the 5303 Å line was carried out and the behaviour of the half widths and equivalent widths were studied in different regions of the corona. The half width of λ5303 increases with distance from the Sun's center in almost all the studied regions (1.2 R⊙ ? r ? 1.7 R⊙). This increase corresponds to an increase of the non-thermal velocities with a gradient of 1–2 km s-1 per 0.1 R⊙. The equivalent widths, expressed in the coronal continuous background intensity remain constant on the average. 相似文献
12.
Using the line profiles of [Fe x] 6374 å and [Fe XIV] 5303 å emission lines observed during five total solar eclipses, we address the problem whether the solar corona is static or contains moving features. Many of the profiles of both emission lines have complicated shapes, which we interpret as an evidence for the existence of many, small, moving features in the corona. The line-of-sight velocities observed by other investigators (e.g. Desai, Chandrasekhar & Angreji 1982) also support this view. On the other hand, about 15 recent interferometric and multislit investigations of coronal emission lines have not shown evidence of moving elements. We suggest that this is due to insufficient spatial resolution. 相似文献
13.
We continued a study of the long-term variations of temperature in the solar corona at all latitudes (Makarov, Tlatov, and
Callebaut, 2002a). The series of the green (Fe xiv 530.3 nm; KI5303) and red (Fe x 637.4 nm; KI6374) coronal intensities for 1957–2002 has been obtained using the coronal observations at the Kislovodsk Solar Station. The
mean monthly coronal intensities have been calculated at all latitudes (0–90˚) and in the high latitude (45–90˚) zones. It was found that the value of KI6374/KI5303increased about 2.0 times at the high latitudes during the last 45 years. This corresponds to a decrease of the average temperature
by 0.1 ×106K of the polar corona. We suppose that a polar decrease of coronal temperature is connected with an increase of the area of
polar zones A
PZoccupied by unipolar magnetic fields (Makarov et al., 2002) and, probably, with an increase of the area of polar coronal holes. The maximum ratio KI6374/KI5303is observed during the minimum sunspot activity. 相似文献
14.
Scanning spectrometer measurements in the range 1310–270 Å, observed from the satellite OSO 3, are reported for the solar flare of 2114 UT March 27, 1967. This flare was a long lasting sequence of bursts with EUV spectra consisting of enhanced lines and recombination continua normally emitted from the chromosphere and chromosphere-corona transition region, with unusually small increases in lines normally emited from the corona. An EUV flare spectrum is presented and suggested as one example for interpreting broadband observations of EUV bursts. Any broadband continuum other than known recombination continua contributed less than 6 % of the meassured line and hydrogen recombination continua in the range 270–1310 Å. The ratio of photon flux of Ciii 1176 Å to that of Ciii 977 Å was 0.86, which suggests an ambient density in the region of emission greater than 1012 cm-3 at temperatures near 60000 K. 相似文献
15.
Spectroscopic studies of the solar corona, using the high spatial and spectral resolution 25-cm coronagraph at the Norikura Solar Observatory for equatorial off-limb observations, indicated that the variation of radiance and line width with height is different for different temperature lines. The line width of the forbidden red emission line [Fe x] 6374 Å was found to increase with height, and that of the green emission line [Fe xiv] 5303 Å decreased with height. This had been interpreted in terms of the interaction between different temperature plasmas but needed to be confirmed. Further observations were made on several days during 2004, in two emission lines simultaneously covering the mid-latitude and polar regions to investigate the existence of the observed variation in other parts of the solar corona. In this study, we have analysed several raster scans that cover mid- and high-latitude regions of the off-limb corona in all four bright emission lines [Fe x] 6374 Å, [Fe xi] 7892 Å, [Fe xiii] 10747 Å, and [Fe xiv] 5303 Å. We find that the FWHM of the red line increases with height and that of the green line decreases with height, similar to the observations in the equatorial regions. The line widths are higher in the polar regions for all of the observed emission lines except the green line. Higher values of FWHM in polar regions may imply higher non-thermal velocities, which could be further linked to a non-thermal source powering the solar-wind acceleration, but the reason for the behaviour of the green emission line remains to be explored. 相似文献
16.
Jagdev Singh Takashi Sakurai Kiyoshi Ichimoto S. Muneer A. V. Raveendran 《Solar physics》2006,236(2):245-262
With a view to investigate variations in parameters of coronal emission lines over a large range of radial distance from the limb, raster scans were made with sufficiently long exposure times on several days during September – October 2003. An analysis of the data shows that (i) in most of the coronal structures, the FWHM of the Fe xiv 5303 Å line decreases up to 300″±50″, (ii) the FWHM of the Fe x 6374 Å line increases up to about 200″ and then remains unchanged up to about 500″, and (iii) the FWHMs of the Fe xi 7892 Å and Fe xiii 10747 Å lines show an intermediate behaviour with height. The analysis of the data also shows that the ratio of FWHM of 6374 Å to that of 5303 Å increases from 0.93 at the limb to 1.18 at 200″ above the limb. From this and the ratio of intensities of the two lines we infer that the plasma in steady coronal structures at a height of about 200″ has a temperature of about 1.5 MK and a non-thermal velocity around 17 km s?1. The observations also show that non-homogeneous temperatures and non-thermal velocities largely exist in the lower corona up to about 300″±100″ above the limb. Amplitudes of variations in FWHM of different emission lines with height in the coronal loops are similar to those in the diffuse plasma around the coronal loops. 相似文献
17.
The results of the spectrophotometrical measurements of the polarization in the coronal lines Fe xiv 5303 Å and Fe × 6374 Å are given. Polarization spectrograms were obtained by two spectrographs (prism and echelle types) during the solar eclipse in Mexico on 7 March, 1970 near the region of the second contact at the heights 0.06 to 0.12 R
above the limb. The polarization in the green line is about 30% (for averaged height 1.08 R
). The polarization in the red line is close to the errors of the measurement and does not exceed 6%. A brief discussion of the results is also given. 相似文献
18.
We report measurements of line intensities and line widths for three quiescent prominences observed with the Naval Research Laboratory slit spectrograph on ATM/Skylab. The wavelengths of the observed lines cover the range 1175 Å to 1960 Å. The measured intensities have been calibrated to within approximately a factor 2 and are average intensities over a 2 arc sec by 60 arc sec slit. We derive nonthermal velocities from the measured line widths. The nonthermal velocity is found to increase with temperature in the prominence transition zone. Electron densities and pressures are derived from density sensitive line ratios. Electron pressures for two of the prominences are found to lie in the range 0.04–0.08 dyn cm–2, while values for the third and most intense and active of the three prominences are in the range 0.07–0.22 dyn cm–2. 相似文献
19.
Wilhelm K. Lemaire P. Curdt W. Schühle U. Marsch E. Poland A. I. Jordan S. D. Thomas R. J. Hassler D. M. Huber M. C. E. Vial J.-C. Kühne M. Siegmund O. H. W. Gabriel A. Timothy J. G. Grewing M. Feldman U. Hollandt J. Brekke P. 《Solar physics》1997,170(1):75-104
SUMER – the Solar Ultraviolet Measurements of the Emitted Radiation instrument on the Solar and Heliospheric Observatory (SOHO) – observed its first light on January 24, 1996, and subsequently obtained a detailed spectrum with detector B in the wavelength range from 660 to 1490 Å (in first order) inside and above the limb in the north polar coronal hole. Using detector A of the instrument, this range was later extended to 1610 Å. The second-order spectra of detectors A and B cover 330 to 805 Å and are superimposed on the first-order spectra. Many more features and areas of the Sun and their spectra have been observed since, including coronal holes, polar plumes and active regions. The atoms and ions emitting this radiation exist at temperatures below 2 × 106 K and are thus ideally suited to investigate the solar transition region where the temperature increases from chromospheric to coronal values. SUMER can also be operated in a manner such that it makes images or spectroheliograms of different sizes in selected spectral lines. A detailed line profile with spectral resolution elements between 22 and 45 mÅ is produced for each line at each spatial location along the slit. From the line width, intensity and wavelength position we are able to deduce temperature, density, and velocity of the emitting atoms and ions for each emission line and spatial element in the spectroheliogram. Because of the high spectral resolution and low noise of SUMER, we have been able to detect faint lines not previously observed and, in addition, to determine their spectral profiles. SUMER has already recorded over 2000 extreme ultraviolet emission lines and many identifications have been made on the disk and in the corona. 相似文献
20.
An analysis of the 4571 Å line of neutral magnesium is presented in which one-dimensional macroscopic velocity fields are included. It is shown that gradients over restricted heights in the vertical and horizontal components of the velocity field of order -0.005 s–1 and -0.004 s–1 (such that velocity towards the observer decreases as height increases), respectively, result in asymmetries in the computed line profile similar to those observed. The heights in the solar atmosphere at which these velocity gradients exist are shown to be very critical in reproducing the observations. It was found that the best results were obtained when the gradients existed in the height range from 200 km to 300 km below the temperature minimum. The results indicate that for the Mg i 4571 Å line model calculations that do not include one-dimensional flow velocities may safely be compared with frequency-averaged observations. 相似文献