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1.
Nine coronal emission lines representing five stages of Fe ionization and one stage of Ni were observed in an enhanced coronal region. The data from these observations are presented along with a density model of the enhanced region obtained from the FeXIII and NiXV emission line ratios as a function of position angle. The electron densities obtained from FeXIII lines range from N
e = 108 to 109 cm–3, and are slightly lower for NiXV line data. Estimates of the variation of temperature over the enhanced region are inferred from the observed line intensities. 相似文献
2.
We present here the results of emission tomography studies, based on a new differential deconvolution method (DDM) of Laplace transform inversion, which we use for reconstruction of the coronal emission measure distributions in the quiet Sun, coronal holes and plage areas. Two methods are explored. The first method is based on the deconvolution of radioemission brightness spectra in a wide wavelength range (1 mm–100 cm) for temperature profile reconstructions from the corona to the deeper chromosphere. The second method uses radio brightness measurements in the cm–dm range to give a coronal column emission measure (EM).Our results are based on RATAN-600 observations in the range 2.0–32 cm supplemented by the data of other observatories during the period near minimum solar activity. This study gives results that agree with known estimates of the coronal EM values, but reveals the absence of any measurable quantities of EM in the transition temperature region 3 × 104 –105 K for all studied large-scale structures. The chromospheric temperature structure (T
e = 20,000–5800 K) is quite similar for all objects with extremely low-temperature gradients at deep layers.Some refraction effects were detected in the decimeter range for all Types of large-scale structures, which suggests the presence of dense and compact loops (up to N
e =(1–3)× 109 cm-3 number density) for the quiet-Sun coronal regions with temperature T
e > 5× 10-5 K. 相似文献
3.
A rocket-borne coronagraph utilizing external occulting disks was used to photograph the solar corona from 3 to 9 R
s at 1931 UT on 7 March, 1970. Comparison of the rocket and ground-based observations shows a one-to-one correspondence between major streamers from the inner to the outer corona. In particular streamers over the poles are clearly visible against the background corona from 3 to 8 R
s. These rocket data had a scattered light level of 1.2 × 10–10
B
s. The derived quiet equatorial and polar K + F corona was within 10% of the absolute brightness of standard coronal models and displayed identical radial gradients to those models. The photometric profiles of the NE limb streamer were analyzed assuming a model in which the core density follows a Gaussian distribution in directions perpendicular to the radius vector. This streamer was assumed to be rooted on the visible disk at 55 to 60° from the plane-of-the-sky as based on K-coronameter and XUV data. An uncertainty of as much as a factor of three still remains for the value of the axis density owing to uncertainty in the line-of-sight dimension of the streamer. 相似文献
4.
Measurements of the solar X-ray spectrum between 3 Å and 15 Å are reported. They were made with two slitless Bragg crystal spectrometers flown on a Sun-pointed Skylark rocket on 8 August, 1967.The use of a beryl crystal has provided higher spectral resolution than hitherto in the spectral range 12 Å and 15 Å leading, in particular, to a revised identification of the strong line at 13.71 Å. Separate components of the stronger emission lines are clearly seen from each of three coronal active regions which may be identified on radio and X-ray spectroheliograms.The absolute line fluxes are used to determine a model for each active region in terms of the differential emission measure as a function of electron temperature. Emission lines due to the transition 1s
2
1
S
0 – 1s2s
3
S
1 in several helium-like ions are identified and values of the local electron density derived from measurement of the line flux in these ions. 相似文献
5.
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
6.
Richard R. Fisher 《Solar physics》1971,19(2):440-450
Observations of the post-flare loop system formed after the east limb proton flare of 12 August 1970 include (a) sets of filtergrams from which photographic subtractions have been constructed and (b) spectra from which a distribution of electron density as a function of temperature for three coronal regions are derived. The filtergrams show no indications of radial velocities in excess of 80 km/s. The spectra indicate an increase in density at the tops of the loops with most of the material at a relatively cool temperature: N
6.0 × 1010, T = 3 × 105K. The distribution functions obtained for areas just above and just below loops indicate a lower electron density and the presence of material at high temperatures, N
2.0 × 1010 and T 2.6 × 106K (above the loops) and T
e
> > 4.4 × 106K for material below the loops. 相似文献
7.
R. Grant Athay 《Solar physics》1973,29(2):357-364
Mean density models of the solar corona show evidence for two distinctive density regimes characterized by different density gradients. High density gradients are identified with regions of predominantly open magnetic lines of force and low density gradients are identified with regions of predominantly closed magnetic lines of force. Spectroscopic data yielding equivalent widths of forbidden lines of Fe x and Fe xiv strongly suggest that the coronal temperature for r > 2.5 R
decreases considerably less rapidly in equatorial regions than r
–2/7, which is the decrease predicted by conduction models with open field lines.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
8.
Maps of the brightness distribution of the ‘quiet Sun’ at 80 and 160 MHz reveal the presence of features both brighter and darker than average. The ‘dark’ regions are well correlated with dark regions on UV maps; we deduce that they result from ‘coronal holes’. The ‘bright’ regions are associated with quiescent filaments and not plages or bright regions on microwave or UV maps; we deduce that they result from ‘coronal helmets’.
When coronal holes appear near the centre of the disk we can estimate the density and kinetic temperature in the holes from the radio observations. For a hole observed on 1972 July 20–21, we find T ≈ 0.8 × 106 inside the hole and T ≈ 1.0 × 106 in average regions outside the hole. Inside the hole the density is estimated to be about one-quarter of that in Newkirk's model of the spherically symmetric corona.
Variations in brightness at a fixed height above the limb are generally well correlated with scans at a similar height made with a K-coronameter. Occasional differences may result from streamers protruding beyond the limb from the back of the Sun. These can be seen by the K-coronameter but, because of refraction of the radio rays, not by the radio-heliograph.
相似文献9.
Slow magnetohydrodynamic (MHD) standing wave oscillations in hot coronal loops for both strong (i.e. τd/P∼ 1) and weak (i.e. τd/P≥ 2) damping are investigated taking account of viscosity, thermal conductivity and optically thin radiation. The individual
effect of the dissipative terms is not sufficient to explain the observed damping. However, the combined effect of these dissipative
terms is sufficient to explain the observed strong damping, as well as weak damping seen by SUMER. We find that, the ratio
of decay time (τd) and period (P) of wave, i.e., τd/P (which defines the modes of damping, whether it is strong or weak) is density dependent. By varying density from 108 to 1010 cm−3 at a fixed temperature in the temperature range 6 – 10 MK, observed by SUMER, we get two sets of damping: one for which τ
d/P∼ 1 corresponds to strong damping that occurs at lower density and another that occurs at higher density for which τd/P ≥ 2 corresponds to weak damping. Contrary to strong-damped oscillations, the effect of optically thin radiation provides
some additional dissipation apart from thermal conductivity and viscosity in weak-damped oscillations. We have, therefore,
derived a resultant dispersion relation including the effect of optically thin radiation. Solutions of this dispersion relation
illustrate how damping time varies with physical parameters of loops in both strong and weak damping cases. 相似文献
10.
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
11.
R. Mewe 《Solar physics》1972,22(2):459-491
The fluxes of about 230 spectral lines in the range 1–60 Å from coronal ions of C, N, O, Ne, Na, Mg, Al, Si, S, Ar, K, Ca, Ti, Cr, Mn, Fe, and Ni are computed for a range of electron temperature from 105 to 109 K. The relative ion abundances are derived from Jordan's ionization equilibrium calculations. The continuum emission is derived from computations of Landini and Monsignori Fossi with a correction for the free-free emission. 相似文献
12.
Werner M. Neupert 《Solar physics》1967,2(3):294-315
The observation of extreme ultraviolet (EUV) emission lines of Fe ix through Fe xvi made by Orbiting Solar Observatory-1 are discussed and applied to a study of the solar corona above active regions. Ultraviolet and radio emission are determined and compared for several levels of activity classified according to the type of sunspot group associated with the active region. Both radio emission and line radiation from Fe xvi, the highest stage of ionization of Fe observed, are observed to increase rapidly with the onset of activity and are most intense over an E-spot group early in the lifetime of the active region. As activity diminishes, radiation from Fe xv and Fe xvi becomes relatively more prominent. The observations imply that the coronal temperature reaches a maximum during the period of highest activity, as indicated by sunspot-group complexity and the occurrence of chromospheric flares. A maximum coronal electron temperature of 4.0 × 106 °K is estimated when taking into account the mechanism of dielectronic recombination. Concurrently, the average coronal electron density increases by a factor of 10–12. Both electron temperature and density decrease as activity subsides. The coronal temperature above the remaining Ca ii plage is estimated to be 2.5–3.0 × 106 °K after flare activity has ceased and sunspots have disappeared. 相似文献
13.
Tokio Tsubaki 《Solar physics》1975,43(1):147-175
A technique developed for analysing line profiles with both speed and high accuracy was used to study the physical conditions
of a coronal formation near a quiescent prominence. Detailed analyses of five coronal lines (Fe xiv λ 5303, Fe x λ 6374, Ni xv λ 6702, Fe xv λ 7059, and Fe xi λ 7892) provided total intensities, Doppler width temperatures, ionization temperatures, and velocities.
Dissimilar spatial fluctuations in intensity are obvious for ions grouped according to (low vs high) ionization potentials.
The intensity of the green line shows a local minimum around the observed quiescent prominence; a corresponding but much more
diffuse pattern is visible in the red line intensity.
Large differences are observed in temperatures derived by different means. In particular,
, while
, and
. The differences between
and
are taken as direct evidence of temperature inhomogeneity. One can thus put little significance in T
e
(xi/x). T
D(λ5303) and T
e
(xv/xiv) fluctuate nearly in parallel at each slit height, with a weak local minimum evident around the prominence. The discrepancy
between these two can be removed if a non-thermal turbulent motion of 6–16 km s−1 is assumed. Variations with height of both T
D(λ5303) and T
e
(xv/xiv) suggest that the coronal temperature maximum is located no more than 15000 km above the top of spicules. A negative gradient
of about 6 deg km−1 is found in the height variation of T
D(λ5303).
The height variation of the green line wavelength shows that the majority of coronal material in this region is flowing from
west to east on the Sun, with the highest velocity of 12 km s−1 found at the lowest heights. This motion is in the same sense as that of the nearby coronal rain, as determined both from
the spectra and wavelength-shifted Hα filtergrams. Superposed on the above flow is a systematic velocity field of up to ±5
km s−1. This field similarly reaches maximum amplitudes at lowest heights showing a local maximum around the prominence.
On leave from Institute of Earth Science and Astrophysics, Shiga University, Ohtsu 520, Japan, as 1973–75 National Academy
of Science/National Research Council Senior Post-Doctoral Research Associate at Sacramento Peak Observatory. 相似文献
14.
Peter Jenniskens Ed Tedesco Jayant Murthy Christophe O. Laux Stephen Price 《Meteoritics & planetary science》2002,37(8):1071-1078
Abstract— We used the ultraviolet to visible spectrometers onboard the midcourse space experiment to obtain the first ultraviolet spectral measurements of a bright meteor during the 1997 Leonid shower. The meteor was most likely a Leonid with a brightness of about‐2 magnitude at 100 km altitude. In the region between 251 and 310 nm, the two strongest emission lines are from neutral and ionized magnesium. Ionized Ca lines, indicative of a hot T ? 10 000 K plasma, are not detected. The Mg and Mg+ line intensity ratio alone does not yield the ionization temperature, which can be determined only by assuming the electron density. A typical air plasma temperature of T = 4400 K would imply a very high electron density: ne = 2.2 times 1018 m‐3, but at chondritic abundances of Fe/Mg and Si/Mg ? 1. For a more reasonable local‐thermodynamic‐equilibrium (LTE) air plasma electron density, the Mg and Mg+ line ratio implies a less than chondritic Fe/Mg = 0.06 abundance ratio and a cool non‐LTE T = 2830 K ionization temperature for the ablation vapor plasma. The present observations do not permit a choice between these alternatives. The new data provide also the first spectral confirmation of the presence of molecular OH and NO emission in meteor spectra. 相似文献
15.
In this paper we utilize the latitude distribution of the coronal temperature during the period 1984–1992 that was derived in a paper by Guhathakurta et al, 1993, utilizing ground-based intensity observations of the green (5303 Fe XIV) and red (6374 Fe X) coronal forbidden lines from the National Solar Observatory at Sacramento Peak, and estabish its association with the global magnetic field and the density distributions in the corona. A determination of plasma temperature,T, was estimated from the intensity ratio Fe X/Fe XIV (whereT is inversely proportional to the ratio), since both emission lines come from ionized states of Fe, and the ratio is only weakly dependent on density. We observe that there is a large-scale organization of the inferred coronal temperature distribution that is associated with the large-scale, weak magnetic field structures and bright coronal features; this organization tends to persist through most of the magnetic activity cycle. These high-temperature structures exhibit time-space characteristics which are similar to those of the polar crown filaments. This distribution differs in spatial and temporal characterization from the traditional picture of sunspot and active region evolution over the range of the sunspot cycle, which are manifestations of the small-scale, strong magnetic field regions.affiliated to USRA 相似文献
16.
Résumé Les populations des niveaux excités des ions coronaux suivent avec une très bonne approximation une loi analytique du type a × N
e
b, où N
e est la densité électronique du milieu et où a et b sont des coefficients dépendant seulement de la distance du bord et de la température. Cette forme est particulièrement souple d'emploi pour l'interprétation des mesures d'intensités des raies démission coronales.Les coefficients a et b présentés ici, ont été déterminés à partir des résultats de nombreux auteurs, et portent sur les niveaux intervenant dans les transitions responsables des raies observées dans le domaine visible et infra-rouge du spectre coronal concernant les ions: Fe x, xi, xiii, xiv, xv; Ca xiii, xv; Ni xii, xiii, xv, xvi et A xiv. L'examen des coefficients b permet notamment de sélectionner les raies les plus sensibles à la densité électronique.
The populations of the excited levels of coronal ions follow with very great accuracy an analytical law of the type a × N e b, where N e is the electron density of the medium and where a and b are only temperature and solar limb distance dependant coefficients. This form is particularly well adapted for the interpretation of the intensities measurements of coronal emission lines.The coefficients a and b here presented have been determined according to the results of various authors, and deal with the levels concerning the transitions responsible for the lines observed in the visible and infrared coronal field, and chiefly bear on the following ions: Fe x, xi, xiii, xiv, xv; Ca xiii, xv; Ni xii, xiii, xv, xvi, and A xiv. The most sensitive lines to the electron density can be selected thanks to the examination of the coefficient b.相似文献
17.
During a balloon flight in France on September 13, 1971, at altitude 32 000 m, the solar corona was cinematographed from 2 to 5R
during 5 hr, with an externally occulted coronagraph.Motions in coronal features, when they occur, exhibit deformations of structures with velocities not exceeding a few 10 km s–1; several streamers were often involved simultaneously; these variations are compatible with magnetic changes or sudden reorganizations of lines of forces.Intensity and polarization measurements give the electron density with height in the quiet corona above the equator. Electron density gradient for one of the streamers gives a temperature of 1.6 × 106 K and comparisons with the on-board Apollo 16 coronal observation of 31 July, 1971 are compatible with the extension of this temperature up to 25 R
bd.Three-dimensional structures and localizations of the streamers are deduced from combined photometry, polarimetry and ground-based K coronametry. Three of the four coronal streamers analysed have their axis bent with height towards the direction of the solar rotation, as if the upper corona has a rotation slightly faster than the chromosphere. 相似文献
18.
C. De Loore 《Astrophysics and Space Science》1970,6(1):60-100
Photospheric models were calculated for 90 stars with effective temperatures between 2500 K and 41600 K for five logg-values ranging from 1 to 5. Molecule formation was taken into account. In order to have an idea about possible instabilities in the different stellar layers some quantities, characteristic for convection and turbulence were calculated, such as the Rayleigh-, Reynolds-, Prandtl- and Péclet-numbers. It turned out that all the investigated stars contain unstable layers, including the hottest. Nevertheless, only stars with effective temperatures of 8300 K or less contain layers where the convective energy transport is important. For all stars the convective velocities were calculated and also the generated mechanical fluxes in the convection zones were tabulated.Under the hypothesis that this mechanical energy flux is responsible for the heating of the corona, coronal models were constructed for the Sun and for some stars with effective temperatures between 5000 K and 8320 K for logg-values of 4 or 5.For Main Sequence stars the largest fluxes are generated in F-stars; stars withT
eff=7130 K and logg=4 possess also the hottest and most dense coronas with a computed temperature of 3.7·106 K and logN
e
=10.5.The solar corona computed in this way, on the basis of a photospheric mechanical flux of 0.14·108 erg cm–2 sec–1, has a temperature of 1.3·106 K and logN
e
=9.8. This density is apparently too high, but even when including in the computations all theoretical refinements proposed in the last few years by various authors it does not appear possible to obtain a solar coronal model with a smaller density.However, when taking into account the inhomogeneous structure of the chromosphere and by associating the calculated mechanical fluxes to the coarse mottles, and lower fluxes to the undisturbed regions we find a mean coronal temperature of 1.1·106 K and a mean logN
e
-values of 9. The computed velocity of the solar wind at a distance of 104 km above the photosphere has a value between 7 and 11 km sec–1. These latter values are in fair agreement with the observations. 相似文献
19.
New theoretical emission line ratios for the Be-sequence ions Mgix and Sixi are presented. A comparison with observational data for two solar flares and an active region loop obtained with the Harvard EUV spectrometer and NRL XUV spectroheliograph aboard Skylab reveals that these plasmas are in ionization equilibrium at coronal temperatures. Unfortunately most of the density diagnostics are not particularly useful under solar plasma conditions, as they vary only slightly over the electron density range 108–1013cm–3. However the Sixi ratioI(3
P
e
2 -3
P
o
2)/I(3
P
o
1 –1
S
e
0) is density sensitive in the range 108 to 1010cm–3, which is representative of electron densities found in solar active regions or small flares. 相似文献
20.
The radio observations of the coronal streamers obtained using Clark Lake radioheliograph at 73.8, 50.0, and 38.5 MHz during a period of minimum activity in September 1986 are presented. Streamers appear to correlate with two prominent disk sources whose intensities fluctuated randomly. The variations in half-power diameter of the radio Sun are found to correspond with the variations in the white-light extents of the coronal streamers. It appears that the shape of the radio Sun is not a function of the phase of the solar cycle; instead it depends on the relative positions of the streamers in the corona. The observed peak brightness temperatures,T
B
, of the streamers are found to be very low, being 6 × 104 K.We compute the brightness temperature distribution along the equator by tracing the rays in the coronal plasma. The rays are deflected away by the streamers before reaching the critical density level, whereas they penetrate deeper into the coronal hole for small angles between the line of sight and the streamer axis. As a consequence, it is found that the streamers and coronal holes appear in the calculated equatorial brightness distribution as irregular brightness depressions and enhancements, respectively. The fine structures are found to disappear when the scattering due to small-scale density inhomogeneities is included in the ray-tracing calculations. The required relative level of density fluctuations, 1 = N/N, is found to be greater than 12% to reduce the peak brightness temperature from 106 K to 6 × 104 K for all the three frequencies.On leave from Indian Institute of Astrophysics, Bangalore 560034, India. 相似文献