Fe XV Research Articles

Coronal Magnetography of a Solar Active Region Using Coordinated SERTS and VLA Observations

We observed NOAA region 7563 simultaneously with Goddard Space Flight Center's Solar EUV Rocket Telescope and Spectrogaph (SERTS) and with the Very Large Array (VLA) on 1993 August 17. SERTS obtained spectra in the 280-420 A wavelength range, and images in the lines of Mg IX λ368.1, Fe XV λ284.1, and Fe XVI λ335.4. The VLA obtained microwave images at 20 and 6 cm wavelengths. The microwave emission depends upon the coronal temperature, density, column emission measure, and magnetic field; therefore, the coronal magnetic field can be derived when all of these other quantities are measured. Here we demonstrate this approach by using the SERTS data to derive all the relevant plasma parameters and then fitting the radio observations to a magnetic field model in order to determine the magnetic field structure. We used the method of Monsignori-Fossi & Landini and the coronal elemental abundances of Feldman et al. to derive the differential emission measure (DEM) curve for region 7563 from numerous EUV emission lines in spatially averaged SERTS spectra. A similar curve was estimated for each point (i.e., each pixel or each spatial location) in the two-dimensional region by scaling the average DEM curve with corresponding pixel intensities in the Mg IX, Fe XV, and Fe XVI images. We integrated each such DEM over narrow temperature ranges to obtain the column emission measure (CEM) as a function of temperature, CEM(T). We also obtained electron density measurements from EUV line intensity ratios in the spatially averaged spectrum for several ionization stages of iron. These were used to derive a functional relation between density and temperature, ne(T). We derived the temperature dependence of the coronal magnetic field [B(T)] at each point in the two-dimensional region by incorporating CEM(T) and ne(T) into expressions for the thermal bremsstrahlung and the gyroresonance opacities, and varying B(T) so as to minimize the difference between the calculated and the observed microwave intensities. The resulting calculated 20 and 6 cm microwave intensity images reproduce the observed images very well. We found that thermal bremsstrahlung alone is not sufficient to produce the observed microwave intensities: gyroemission is required. Further, contrary to several earlier studies, we found no evidence for cool, absorbing plasma in the solar corona above the active region. The coronal magnetic fields derived with our method typically exceed the coronal fields extrapolated with a simple potential model, suggesting the presence of coronal electric currents. However, in the diminutive sunspot which dominates the 6 cm emission this difference is relatively small, suggesting that the sunspot magnetic field itself is nearly potential. Although we cannot firmly establish the uniqueness of our solution in this particular case, the method is quite powerful and should be repeated with other similar data sets. Variations in the coronal elemental abundances could affect the determination of the microwave emission mechanism(s), introduce evidence for the presence of cool coronal plasma, and alter the strengths of the derived coronal magnetic fields.

SPECTRAL LINE INTENSITIES FORn= 3–3 EUV TRANSITIONS IN Fe XV

Transition rates and collision strengths between the fine-structure levels of Fe XV have been calculated using the configurations 3s2, 3s3p, 3p2, 3s3d, 3p3d, and 3d2and are compared here with other calculations. The present calculations were carried out using the Superstructure and distorted-wave programs developed at University College, London. Level populations and line intensity ratios are calculated for three temperatures with logTe(K) = 6.2, 6.4, and 6.6 and for electron densitiesNe= 108–1012cm−3. Calculated intensity ratios of the emission lines are compared with those observed by the Solar EUV Rocket Telescope and Spectrograph (SERTS) in an active region of sun. The present results should also be useful in analyzing observations from the Solar Heliospheric Observatory (SOHO).

ATOMIC DATA AND SPECTRAL LINE INTENSITIES FORn= 3–3 ANDn= 3–4 X-RAY TRANSITIONS IN Fe XV

Transition rates, oscillator strengths, and collision strengths between the fine-structure levels of Fe XV have been calculated using the configurations 3s2, 3s3p, 3p2, 3s3d, 3p3d, 3s4s, 3s4p, 3s4d, 3s4f, 3p4s, 3p4p, 3p4d, and 3p4f. The calculations were carried out using the Superstructure and distorted wave programs developed at University College, London, together with a new program, NELMA (no-exchange Limeil–Meudon approximation). Level populations and relative spectral line intensities are calculated for four temperatures with logTe(K) in the range 6.2 to 6.8 and for electron densitiesNe= 108–1012cm−3. These data have been used to investigate the rocket spectrum of a solar flare in the 10–100 Å range. The strong unidentified spectral line at 69.65 Å has been attributed to the transition 3s3p1P1–3s4s1S0.

Extended analysis of spectra and 3l4l energy levels in Mg-like Sc X–Fe XV

Spectra emitted from laser-produced plasmas of Sc, Ti, V, Cr, Mn, and Fe are recorded in the region 50–180 Å. Transitions from 3s4l, 3p4l, and 3d4l levels to the 3, 3 complex were identified, and a large number of previously unknown 3l4l′ levels are established. The identifications are supported by ab initio and parametric calculations and by isoelectronic studies.

The Structure and Properties of Solar Active Regions and Quiet‐Sun Areas Observed in Soft X‐Rays withYohkoh/SXT and in the Extreme‐Ultraviolet with SERTS

We observed two solar active regions (NOAA regions 7563 and 7565), quiet-Sun areas, and a coronal hole region simultaneously with Goddard Space Flight Center's Solar EUV Rocket Telescope and Spectrograph (SERTS) and with the Yohkoh Soft X-ray Telescope (SXT) on 1993 August 17. SERTS provided spatially resolved active region and quiet-Sun slit spectra in the 280 to 420 A wavelength range, and images in the lines of He II λ303.8, Mg IX λ368.1, Fe XV λ284.1, and Fe XVI λλ335.4 and 360.8 SXT provided images through multiple broadband filters in both the full-frame imaging mode and the partial-frame imaging mode. The SERTS images in Fe XV (log Tmax = 6.33, where Tmax is the temperature which maximizes the fractional ion abundance in the available ionization equilibrium calculations, i.e., the formation temperature) and Fe XVI (log Tmax = 6.43) exhibit remarkable morphological similarity to the SXT images. Whereas the Fe XV and XVI images outline the loop structures seen with SXT, the cooler He II (log Tmax = 4.67) and Mg IX (log Tmax = 5.98) images outline loop footpoints. In addition, the Mg IX emission outlines other structures not necessarily associated with the hot loops; these may be cool (T 1 × 106 K) loops. From the spatially resolved slit spectra, we obtained emission-line profiles for lines of He II λ303.8, Mg IX λ368.1, Fe XIII λ348.2, Si XI λ303.3, Fe XIV λ334.2, Fe XV λ284.1, and Fe XVI λ335.4 for each spatial position. Based upon the spatial variations of the line intensities, active region 7563 systematically narrows when viewed with successively hotter lines, and appears narrowest in the broadband soft X-ray emission. The active region width (full width at half-maximum intensity) diminishes linearly with log Tmax; the linear fit yields an extrapolated effective log Tmax of 6.51 ± 0.01 for the X-ray emission. The most intense, central core straddles the magnetic neutral line. Active region and quiet-Sun one-dimensional temperature scans were derived from intensity ratios of spatially resolved SERTS slit spectral lines, and from coregistered SXT filter ratios. The highest plasma temperatures were measured in the most intense, central core of region 7563. The temperatures derived from Fe XVI λ335.4/Fe XV λ284.1 and Fe XVI λ335.4/Fe XIV λ334.2 vary significantly (based upon the measurement uncertainties) but not greatly (factors of less than 1.5) across the slit. The average log T values derived from the above two ratios for region 7563 are 6.39 ± 0.04 and 6.32 ± 0.02, respectively. Somewhat larger systematic variations were obtained from all available SXT filter ratios. The average active region log T values derived from the SXT AlMgMn/thin Al, thick Al/thin Al, and thick Al/AlMgMn filter ratios are 6.33 ± 0.03, 6.45 ± 0.02, and 6.49 ± 0.03, respectively. Active region and quiet-Sun one-dimensional density scans were derived from intensity ratios of spatially resolved SERTS slit spectral lines of Fe XIII and Fe XIV. The derived densities show neither systematic nor significant variations along the slit in either the active region or the quiet-Sun, despite the fact that the intensities themselves vary substantially. This indicates that the product of the volume filling factor and the path length (fΔl) must be greater by factors of 3-5 in the active region core than in the outskirts. Furthermore, the derived active region densities are ~2 times the quiet-Sun densities. This density difference is adequate to explain the factor of ~4 intensity difference in Fe XII and Fe XIII between the active and quiet areas, but it is not adequate to explain the factor of ~8 intensity difference in Fe XIV between the active and quiet areas. We attribute the latter to a greater fΔl in the active regions. Statistically significant Doppler shifts are not detected in region 7563 or in the quiet-Sun with any of the EUV lines.

EIT OBSERVATIONS OF THE EXTREME ULTRAVIOLET SUN

The Extreme Ultraviolet Imaging Telescope (EIT) on board the SOHO spacecraft has been operational since 2 January 1996. EIT observes the Sun over a 45 × 45 arc min field of view in four emission line groups: Fe IX, X, Fe XIIi, Fe xv, and He II. A post-launch determination of the instrument flatfield, the instrument scattering function, and the instrument aging were necessary for the reduction and analysis of the data. The observed structures and their evolution in each of the four EUV bandpasses are characteristic of the peak emission temperature of the line(s) chosen for that bandpass. Reports on the initial results of a variety of analysis projects demonstrate the range of investigations now underway: EIT provides new observations of the corona in the temperature range of 1 to 2 MK. Temperature studies of the large-scale coronal features extend previous coronagraph work with low-noise temperature maps. Temperatures of radial, extended, plume-like structures in both the polar coronal hole and in a low latitude decaying active region were found to be cooler than the surrounding material. Active region loops were investigated in detail and found to be isothermal for the low loops but hottest at the loop tops for the large loops.

Imaging the solar corona in the EUV

The SOHO (SOlar and Heliospheric Observatory) satellite was launched on December 2nd 1995. After arriving at the Earth-Sun (L1) Lagrangian point on February 14th 1996, it began to continuously observe the Sun. As one of the instruments onboard SOHO, the EIT (Extreme ultraviolet Imaging Telescope) images the Sun's corona in 4 EUV wavelengths. The He II filter at 304 Å images the chromosphere and the base of the transition region at a temperature of 5 − 8 × 10 4 K; the Fe IX–X filter at 171 Å images the corona at a temperature of ∼ 1.3 × 10 6 K; the Fe XII filter at 195 Å images the quiet corona outside coronal holes at a temperature of ∼ 1.6 × 10 6 K; and the Fe XV filter at 284 Å images active regions with a temperature of ∼ 2.0 × 10 6 K. About 5000 images have been obtained up to the present. In this paper, we describe also some aspects of the telescope and the detector performance for application in the observations. Images and movies of all the wavelengths allow a look at different phenomena present in the Sun's corona, and in particular, magnetic field reconnection.

The Extreme-Ultraviolet Spectrum of the Nearby K Dwarf epsilon Eridani

view Abstract Citations (37) References (26) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Extreme-Ultraviolet Spectrum of the Nearby K Dwarf ɛ Eridani Schmitt, J. H. M. M. ; Drake, J. J. ; Stern, R. A. ; Haisch, B. M. Abstract We present and discuss the extreme-ultraviolet spectrum of the nearby K2 dwarf ɛ Eri obtained with the spectrometers onboard the Extreme-Ultraviolet Explorer satellite (EUVE). In the EUVE spectrum of ɛ Eri we detect emission lines attributable to iron in the ionization stages Fe IX to Fe XXI, thus covering a rather large temperature range from less than 106 K to 107 K. While the lines in the lowest and highest ionization stages are relatively weak, the strongest lines detected are from Fe XV and Fe XVI, from which we infer a peak in the differential emission measure distribution at coronal temperatures of log Tc ∼ 6.4; significant emission measure is, however, also present at both higher and lower temperatures. This is in contrast to both lower activity stars whose EUV spectra are dominated by cooler Fe lines in the range 170-180 Å as well as the more active stars whose EUV spectra are dominated by hotter Fe lines in the range 110-135 Å. Finally, a density determination using line ratios of Fe XIII and Fe XIV results in coronal densities for ɛ Eri which are similar to solar active region densities. Publication: The Astrophysical Journal Pub Date: February 1996 DOI: 10.1086/176783 Bibcode: 1996ApJ...457..882S Keywords: STARS: CORONAE; STARS: INDIVIDUAL CONSTELLATION NAME: EPSILON ERIDANI; STARS: LATE-TYPE; ULTRAVIOLET: STARS full text sources ADS | data products SIMBAD (7) MAST (2) HEASARC (1)

EIT: Extreme-ultraviolet Imaging Telescope for the SOHO mission

The Extreme-ultraviolet Imaging Telescope (EIT) will provide wide-field images of the corona and transition region on the solar disc and up to 1.5 R⊙ above the solar limb. Its normal incidence multilayer-coated optics will select spectral emission lines from Fe IX (171 A), Fe XII (195 A), Fe XV (284 A), and He II (304 A) to provide sensitive temperature diagnostics in the range from 6 × 104 K to 3 × 10 6 K. The telescope has a 45×45 arcmin field of view and 2.6 arcsec pixels which will provide approximately 5-arcsec spatial resolution. The EIT will probe the coronal plasma on a global scale, as well as the underlying cooler and turbulent atmosphere, providing the basis for comparative analyses with observations from both the ground and other SOHO instruments. This paper presents details of the EIT instrumentation, its performance and operating modes.

Investigation of the electrochemical properties of Fe xV 2O 5

Structural and electrochemical studies have been undertaken on the vanadium bronze Fe x V 2O 5, prepared by a sol-gel process followed by ion-exchange. Using the electrochemical voltage spectroscopy (EVS) technique, an investigation of its electrochemical properties is presented. Three reversible insertion plateaus are present between 2.5 and 3.5 V [versus Li Li + ] corresponding to a faradaic yield of 1.8 moles of lithium per formula unit resulting in an initial energy density of 725 Wh/Kg. A high capacity retention is observed when cells are cycled between 3.75 and 1.9 V versus Li Li + at C 3 rate. 70% of the initial capacity was still maintained after 20 cycles.

A Review of Electron Impact Excitation of Fe XV-Fe XVII

Theoretical electron impact excitation data for Fe XV, Fe XVI, and Fe XVII are critically assessed and recommended data are identified.

Evidence of mass outflow in the low corona over a large sunspot

An extreme ultraviolet (EUV) imaging spectrograph designed for soundings rocket flight has been used to search for velocity fields in the low solar corona. During a flight in May, 1989, we obtained emission line profile measurements along a chord through an active region on the Sun. Relative Doppler velocities were measured in emissions lines of Mg IX, Fe XV, and Fe XVI with a sensitivity of 2–3 km s −1 at 350 A. The only Doppler shift appreciably greater than this level was observed in the line of Mg IX at 368.1 A over the umbra of the large sunspot. The maximum shift measured at that location corresponded to a velocity toward the observer of 14 +/- 3km s −1 relative to the mean of measurements in that emission line made elsewhere over the active region. The magnetic field in the low corona was aligned to within 10° of the line of sight at the location of maximum Doppler shift. Depending on the magnetic field geometry, this mass outflow could either re-appear as a downflow of material in distant footpoints of closed coronal loops or, if along open field lines, could contribute to the solar wind. The site of the sunspot was near a major photospheric magnetic field boundary. Such boundaries have been associated with low-speed solar wind as observed in interplanetary plasmas.

Atomic data for opacity calculations. XIX. The magnesium isoelectronic sequence

As a contribution to the International Opacity Project, large numbers of multiplet term energies, f-values and photoionization cross sections have been calculated for those Mg-like ions of astrophysical interest: Mg I, Al II, Si III, S V, Ar VII, Ca IX and Fe XV. The present atomic data have been obtained in the close-coupling approximation with a modified version of the RMATRX computer program and asymptotic codes. We briefly discuss the new results, and representative comparisons with previous experimental and theoretical work are carried out. Emphasis is given to the large number of photoionization cross sections reported for the first time. We conclude that the statistical accuracy of the Opacity Project datasets for the Mg isoelectronic sequence is at least as high as that of any other set of data produced with the most elaborate methods available to date.

Simultaneous observations of solar plage with the solar extreme ultraviolet rocket telescope and spectrograph (SERTS), the VLA, and the Kitt Peak magnetograph

We obtained simultaneous images of solar plage on 1991, May 7 with SERTS, the VLA,4 and the NASA/National Solar Observatory spectromagnetograph at the NSO/Kitt Peak Vacuum Telescope. Using intensity ratios of Fe XVI to Fe XV emission lines, we find that the coronal plasma temperature is (2.3-2.9) x 10 exp 6 K throughout the region. The column emission measure ranges from 2.5 x 10 exp 27 to l.3 x 10 exp 28 cm exp -5. The calculated structure and intensity of the 20 cm wavelength thermal bremsstrahlung emission from the hot plasma observed by SERTS is quite similar to the observed structure and intensity of the 20 cm microwave emission observed by the VLA. Using the Meyer (1991, 1992) revised coronal iron abundance, we find no evidence either for cool absorbing plasma or for contributions from thermal gyroemission. Using the observed microwave polarization and the SERTS plasma parameters, we calculate a map of the coronal longitudinal magnetic field. The resulting values, about 30-60 G, are comparable to extrapolated values of the potential field at heights of 5000 and 10,000 km.

Identification of the Fe XV 3s3p 1P-3p2 1S line in solar flare spectra and its use as an electron density diagnostic

We have examined EUV spectra of solar flares obtained with the Naval Research Laboratory's S082A slitless spectrograph on board Skylab, and measured the intensities of the 324.97 A and 323.57 A emission lines relative to that of the Fe XV 3s3p 3 P 2 -3p 2 3 P 1 transition at 321.76A. A comparison of these line ratios with theoretical predictions indicates that the Fe XV 3s3p 1 P-3p 2 1 S transition is the line observed at 324.97 A, rather than the feature at 323.57 A as previously suggested. In addition, we show that the I(324.97 A)/I(321.76 A) intensity ratio is an excellent electron density diagnostic for the Fe XV emitting region of the solar atmosphere

Analysis of EUV, Microwave, and Magnetic Field Observations of Solar Plage

AbstractWe obtained simultaneous images of solar plage on 7 May 1991 with Goddard Space Flight Center’s Solar EUV Rocket Telescope and Spectrograph (SERTS), the Very Large Array (VLA), and the NASA/NSO spectromagnetograph at Kitt Peak. Using intensity ratios of Fe XVI to Fe XV emission lines, we find that the coronal plasma temperature is 2.5 ± 0.3 ×lO6 K throughout the region. The column emission measure ranges from 2.6 × 1027 to 1.3 × 1028 cm−5. The calculated structure and intensity of the 20 cm wavelength thermal bremsstrahlung emission from the hot plasma observed by SERTS is quite similar to the observed structure and intensity of the 20 cm microwave emission observed by the VLA. Using the revised coronal iron abundance of Meyer (1991, 1992), we find no evidence for either cool absorbing plasma or for contributions from thermal gyroemission. Combining the observed microwave polarization and the SERTS plasma parameters, we calculate a map of the coronal longitudinal magnetic field. The resulting values, ~ 30 – 60 Gauss, are comparable to extrapolated values of the potential field at heights of 5,000 and 10,000 km.

A burst model for line emission in the solar atmosphere. II - Coronal extreme ultraviolet lines

view Abstract Citations (34) References (20) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Burst Model for Line Emission in the Solar Atmosphere. II. Coronal Extreme Ultraviolet Lines Feldman, U. ; Laming, J. M. ; Mandelbaum, P. ; Goldstein, W. H. ; Osterheld, A. Abstract We review the spectroscopic evidence for explosive events - bursts - occurring in solar coronal plasmas. Problems in the interpretation of extreme ultraviolet spectra from Mg-like ions, particularly Fe XV in solar flares can be obviated to certain extent if these ions are produced in an ionizing plasma, with the 3s3p 3P levels being excited directly by inner shell ionization of the Al-like ion. We believe that a similar mechanism should apply to Be-like ions. The excitation following inner shell ionization can become important compared to electron impact excitation at a temperature corresponding to approximately twice the ionization potential of the ion concerned, but to be properly effective, it requires some deviation of the electron distribution function from a Maxwellian. The model we present produces a coronal heating rate from these bursts that is somewhat larger than current estimates. Publication: The Astrophysical Journal Pub Date: October 1992 DOI: 10.1086/171893 Bibcode: 1992ApJ...398..692F Keywords: Emission Spectra; Solar Atmosphere; Solar Corona; Solar Radio Bursts; Ultraviolet Spectra; Line Spectra; Plasma Heating; Solar Flares; Solar Physics; ATOMIC DATA; ATOMIC PROCESSES; PLASMAS; SUN: CORONA full text sources ADS | Related Materials (2) Part 1: 1992ApJ...386..364L Part 3: 1993ApJ...404..799F

Evidence for mass outflow in the low solar corona over a large sunspot

Spatially resolved EUV coronal emission-line profiles have been obtained in a solar active region, including a large sunspot, using an EUV imaging spectrograph. Relative Doppler velocities were measured in the lines of Mg IX, Fe XV, and Fe XVI with a sensitivity of 2-3 km/s at 350 A. The only significant Doppler shift occurred over the umbra of the large sunspot, in the emission line of Mg IX (at Te of about 1.1 x 10 exp 6 K). The maximum shift corresponded to a peak velocity toward the observer of 14 +/- 3 km/s relative to the mean of measurements in this emission line made elsewhere over the active region. The magnetic field in the low corona was aligned to within 10 deg of the line of sight at the location of maximum Doppler shift. Depending on the closure of the field, such a mass flow could either contribute to the solar wind or reappear as a downflow of material in distant regions on the solar surface. The site of the source, near a major photospheric field boundary, was consistent with origins of low-speed solar wind typically inferred from interplanetary plasma observations.

Fe XV line ratios in the sun - Discrepancies between theory and observations

Les taux de collision d'impacts electroniques, determines avec la methode de la matrice R, sont presentes pour Fe XV. Les rapports d'intensite de raies sont determines pour les eruptions solaires du 17 decembre et du 9 aout 1973 et du 21 janvier 1974 et compares aux observations

The 3d2 configuration in Ca IX-Zn XIX

Spectra emitted from laser produced plasmas of Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn have been recorded in the region 170-800 Å. In magnesium-like Ca IX to Mn XIV transitions establishing the 1D, 3F and 1G terms of 3d2 have been identified. The 3F and 1G terms are reported also for Fe XV to Zn XIX.Ab initio calculations support the identifications and provide LSJ eigenvector components for the energy levels.