scholarly journals The solar corona above active regions: a comparison of extreme ultraviolet line emission with radio emission

1968 ◽  
Vol 35 ◽  
pp. 404-410 ◽  
Author(s):  
Werner M. Neupert
Keyword(s):  
Active Region ◽  
Radio Emission ◽  
Solar Corona ◽  
Extreme Ultraviolet ◽  
Line Emission ◽  
Active Regions ◽  
Emission Lines ◽  
Line Radiation ◽  
X Ray ◽  
Spot Group

The observations of extreme ultraviolet (EUV) emission lines of Feix through Fe XVI made by OSO-I have been applied to a study of the solar corona above active regions. Ultraviolet and radio emission are determined 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 XIV becomes relatively more prominent. Preliminary X-ray data from OSO-III obtained during a flare are introduced. These indicate that radiation from the highest stage of iron thus far observed, Fe XXV, reaches a maximum first in an X-ray burst and that maxima in lower stages of ionization follow, with delays from 2 to 15 min.

scholarly journals Statistical Properties of Magnetic Separators in Model Active Regions

2000 ◽  
Vol 195 ◽  
pp. 443-444
Author(s):  
B. T. Welsch ◽  
D. W. Longcope
Keyword(s):  
Active Region ◽  
Solar Corona ◽  
Magnetic Reconnection ◽  
First Principles ◽  
Magnetic Charge ◽  
Active Regions ◽  
Heating Rates ◽  
X Ray ◽  
Field Lines ◽  
Charge Topology

“Transient brightenings” (or “microflares”) regularly deposit 1027 ergs of energy in the solar corona, and account for perhaps 20% of the active corona's power (Shimizu 1995). We assume these events correspond to episodes of magnetic reconnection along magnetic separators in the solar corona. Using the techniques of magnetic charge topology, we model active region fields as arising from normally distributed collections of “magnetic charges”, point-like sources/sinks of flux (or field lines). Here, we present statistically determined separator (X-ray loop) lengths, derived from first principles. We are in the process of statistical calculations of heating rates due to reconnection events along many separators.

X-radiation studies of the corona

1968 ◽  
Vol 35 ◽  
pp. 431-431
Author(s):  
K. A. Pounds ◽  
K. Evans ◽  
P. C. Russell
Keyword(s):  
Active Region ◽  
Solar Disk ◽  
Line Emission ◽  
Emission Lines ◽  
Strong Line ◽  
List Type ◽  
Wave Band ◽  
Uv Spectrum ◽  
X Ray ◽  
Aspect Angle

The coronal X-ray emission has been studied in a series of sunpointed Skylark-rocket flights over the period August 1964 to August 1967. Two types of instrument have been used, namely, an array of pinhole cameras, to study the distribution of X-ray sources across the solar disk, and a set of Bragg crystal spectrometers, to examine the detailed spectrum of the emission.Six rocket flights in all (Skylarks 301, 302, 303, 306, 307, and 406) have provided solar X-ray photographs, covering the wave-band 12–60 Å. The main conclusions of this work may be summarised as follows: (1)Of over twenty separate calcium-plages areas, all those having an area-intensity product greater than 300 were associated with enhanced coronal X-radiation, this ‘threshold’ being merely a function of X-ray camera sensitivity.(2)The plages studied were of from 1st to 4th rotation, indicating the enduring nature of the local coronal X-ray enhancement.(3)Crude spectral analysis, derived from different filters used in a given camera array, showed an increasing contrast between the active region and disk emissions below 25 Å, indicating the probability of the active region coronal material being rather hotter.(4)Photographs of regions on the disk and on the limb showed a typical coronal active region to produce more than 50% of its total X-ray flux from a region within 1 arc minute cube. Electron densities up to 10 times the normal coronal values are required by the measured X-ray brightness of the larger regions.(5)The major part of the emission above 20 Å arises from the (cooler) background corona. Examination of this coronal disk emission revealed strong limb brightening, polar darkening (particularly in the 1964–65 photographs) and a band of slightly enhanced X-radiation near latitude 35 °N. The latter observation was noted on successive flights, in October 1965 and February 1966, and clearly followed the tilt in aspect angle of the solar disk.Skylarks 304 and 305 were equipped with uncollimated Bragg crystal spectrometers. The former payload, flown in May 1966, revealed strong line emission down to the scan limit at 11 Å. Emission lines of O VII and VIII, Ne IX and X, Fe XVII and XVIII and NI XIX have been identified. All but the O VII series were found to have dominant components arising from a large active region on the solar disk, and an analysis has shown that the complete active-region spectrum is consistent with an electron temperature of 3 million degrees. Intercomparison of the different emission lines indicated coronal abundances of iron, nickel and neon comparable to those derived earlier by Pottasch from an analysis of the solar UV spectrum.Provisional analysis of the latest flight (Skylark 305 in August 1967), employing crystals of beryl and EDDT in addition to the KAP flown on Skylark 304, has shown strong emission lines of the helium-like ions Mg XI and Si XIII, with weaker but significant intensity in Lyman-α of Mg XII (8·4 Å) and Si XIV (6·2 Å), the latter emission requiring the presence of active region material at a temperature of near 107°K.

scholarly journals Silicon in the solar corona

1965 ◽  
Vol 23 ◽  
pp. 115-123
Author(s):  
K. G. Widing ◽  
J. R. Porter
Keyword(s):  
Solar Corona ◽  
Relative Intensity ◽  
Line Emission ◽  
X Ray ◽  
Resonance Transitions ◽  
Spectral Ranges

Resonance lines of coronal ions of silicon are prominent in the spectral ranges 40–62 Å and 254–356 Å.An unexpected feature of the soft X-ray spectrum is the weakness or absence of the resonance lines of iron in ionization stages XI through XV.A second feature is the prominence of lines of the type (3d → 2p) relative to the resonance transitions (3p → 2s) in Li-like and Beryllium-like spectra. It is suggested that the upper levels (3d) are excited by quadrupole collisions from the ground 2s or 2s2levels.The intensity of the soft X-ray lines relative to the resonance lines in the 300 Å region seems to be more consistent with temperatures well above one million degrees than with temperatures as low as 700000°K, but the data are not adequate for a precise comparison. The relative intensity of the line emission from the various stages of silicon ionization may be interpreted as indicating that the ionization of silicon peaks in stages IX and X.The abundances of C, Mg, S, and Al relative to silicon do not seem to be greatly different from the chromospheric abundances reported by Pottasch or with the photospheric abundances.

scholarly journals LOFAR observations of the quiet solar corona

2018 ◽  
Vol 614 ◽  
pp. A54 ◽  
Author(s):  
C. Vocks ◽  
G. Mann ◽  
F. Breitling ◽  
M. M. Bisi ◽  
B. Dąbrowski ◽  
...  
Keyword(s):  
Radio Emission ◽  
Solar Corona ◽  
Density Profile ◽  
Extreme Ultraviolet ◽  
Low Frequency ◽  
Scale Height ◽  
Solar Radio Emission ◽  
Radial Magnetic Field ◽  
Brightness Temperatures ◽  
Hydrostatic Model

Context. The quiet solar corona emits meter-wave thermal bremsstrahlung. Coronal radio emission can only propagate above that radius, Rω, where the local plasma frequency equals the observing frequency. The radio interferometer LOw Frequency ARray (LOFAR) observes in its low band (10–90 MHz) solar radio emission originating from the middle and upper corona. Aims. We present the first solar aperture synthesis imaging observations in the low band of LOFAR in 12 frequencies each separated by 5 MHz. From each of these radio maps we infer Rω, and a scale height temperature, T. These results can be combined into coronal density and temperature profiles. Methods. We derived radial intensity profiles from the radio images. We focus on polar directions with simpler, radial magnetic field structure. Intensity profiles were modeled by ray-tracing simulations, following wave paths through the refractive solar corona, and including free-free emission and absorption. We fitted model profiles to observations with Rω and T as fitting parameters. Results. In the low corona, Rω < 1.5 solar radii, we find high scale height temperatures up to 2.2 × 106 K, much more than the brightness temperatures usually found there. But if all Rω values are combined into a density profile, this profile can be fitted by a hydrostatic model with the same temperature, thereby confirming this with two independent methods. The density profile deviates from the hydrostatic model above 1.5 solar radii, indicating the transition into the solar wind. Conclusions. These results demonstrate what information can be gleaned from solar low-frequency radio images. The scale height temperatures we find are not only higher than brightness temperatures, but also than temperatures derived from coronograph or extreme ultraviolet (EUV) data. Future observations will provide continuous frequency coverage. This continuous coverage eliminates the need for local hydrostatic density models in the data analysis and enables the analysis of more complex coronal structures such as those with closed magnetic fields.

A Discussion on the physics of the solar atmosphere - Spectroscopic studies of the solar corona at x-ray wavelengths

1976 ◽  
Vol 281 (1304) ◽  
pp. 383-390 ◽  
Keyword(s):  
Spatial Distribution ◽  
Solar Corona ◽  
Spatial Variation ◽  
Resonance Line ◽  
Active Regions ◽  
Resonance Scattering ◽  
Spectroscopic Studies ◽  
Line Of Sight ◽  
X Ray ◽  
Forbidden Transitions

The spatial distribution of the emission in several X-ray lines is discussed with emphasis on temperature dependence and association with active regions. New results are presented for the trio of helium-like O vii lines which demonstrate (1) a spatial variation in the density dependent forbidden to intersystem line ratio, and (2) a strong spatial variation in the intensity of the O vii resonance line relative to the optically forbidden transitions. The second effect appears to be caused by resonance scattering by material in the line of sight.

scholarly journals Dissecting the EUV Spectrum of Capella

1996 ◽  
Vol 152 ◽  
pp. 105-112 ◽  
Author(s):  
Nancy S. Brickhouse
Keyword(s):  
Extreme Ultraviolet ◽  
Emission Measure ◽  
Continuous Distribution ◽  
Line Emission ◽  
Local Maximum ◽  
Abundance Ratio ◽  
Emission Lines ◽  
Cool Star ◽  
The Individual ◽  
The Continuum

Extreme ultraviolet spectra of Capella, obtained at various orbital phases over the past two years by the EUVE satellite, show strong emission lines from a continuous distribution of temperatures (~ 105 − 107.3 K). In addition to the strong He II λ303.8, the spectra are dominated by emission lines of highly ionized iron. Strong lines of Fe IX, XV, XVI, and XVIII–XXIV are used to construct emission measure distributions for the individual pointings, which show several striking features, including a minimum near 106 K and a local maximum at 106.8 K. Furthermore, intensities of the highest temperature lines (Te > 107 K) show variations (factors of 2–3) at different orbital phases, while the lower temperature Fe lines show variations of about 30% or less. The low variability of most of the strong low temperature features motivates a detailed analysis of the summed spectrum. With ~ 280 ks of total exposure time, we have measured over 200 emission features with S/N ≥ 3.0 in the summed spectrum. We report here initial results from the analysis of this spectrum. We can now identify lines of Fe VIII and X–XIV, as well as a number of electron density and abundance diagnostic lines.We also report here the first direct measurement of the continuum flux around ~ 100 Å in a cool star atmosphere with EUVE. The continuum flux can be predicted from the emission measure model based on Fe line emission, and demonstrates that the Fe/H abundance ratio is close to the solar photospheric value.

scholarly journals Dynamic Events in the X-Ray Corona (A Progress Report from the AS&E X-ray Telescope on Skylab)

1974 ◽  
Vol 57 ◽  
pp. 501-504 ◽  
Author(s):  
G. S. Vaiana ◽  
A. S. Krieger ◽  
J. K. Silk ◽  
A. F. Timothy ◽  
R. C. Chase ◽  
...  
Keyword(s):  
Active Region ◽  
Large Scale ◽  
Active Regions ◽  
Loop Structure ◽  
X Ray ◽  
Dynamic Events ◽  
Coronal Bright Points ◽  
Coronal Activity ◽  
East Limb ◽  
Coronal Structures

Data obtained by the AS&E X-ray Telescope Experiment during the first Skylab mission have revealed a variety of temporal changes in both the form and brightness of coronal structures. Dynamical changes have been noted in active regions, in large scale coronal structures, and in coronal bright points. The coronal activity accompanying a series of Hα flares and prominence activity between 0800 and 1600 UT on 10 June 1973 in active region 137 (NOAA) at the east limb is shown in Figure 1. It is characterized by increases in the brightness and temperature of active region loops and a dramatic change in the shape and brightness of a loop structure. Figure 2 shows the reconfiguration of an apparent polar crown filament cavity between 1923 UT on 12 June 1973 and 1537 UT on 13 June 1973. A ridge of emitting material which attains a peak brightness at least four times that of the surrounding coronal structures appears within the cavity during the course of the event. Typical X-ray photographs with filters passing relatively soft X-ray wavelengths (3–32, 44–54 Å) show 90 to 100 X-ray bright points (Vaiana et al., 1973). On twelve occasions in the data from the first mission, such bright points were seen to increase in intensity by two orders of magnitude in less than 4 min. Such an event is shown in Figure 3.

scholarly journals Highly Ionized sodium X-ray line emission from the solar corona and the abundance of sodium

2010 ◽  
Vol 518 ◽  
pp. A41 ◽  
Author(s):  
K. J. H. Phillips ◽  
K. M. Aggarwal ◽  
E. Landi ◽  
F. P. Keenan
Keyword(s):  
Solar Corona ◽  
Line Emission ◽  
X Ray
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