Solar EUV Rocket Telescope And Spectrograph Research Articles

Atomic data and spectral line intensities for Mg V

Electron impact collision strengths, energy levels, oscillator strengths, and spontaneous radiative decay rates are calculated for Mg V. The configurations used are 2s 22p 4, 2s2p 5, 2p 6, 2s 22p 33s, 2s 22p 33p, and 2s 22p 33d, giving rise to 86 fine-structure levels in intermediate coupling. Collision strengths are calculated at five incident energies, 10, 20, 30, 40, and 50 Ry, in the distorted wave approximation. Excitation rate coefficients (not tabulated here) are calculated as a function of electron temperature by assuming a Maxwellian electron velocity distribution. To calculate excitation rate coefficients, collision strengths at low and high energy limits are calculated by a method described by Burgess and Tully. Using the excitation rate coefficients and the radiative transition rates, statistical equilibrium equations for level populations are solved at electron densities covering the range of 10 8–10 14 cm −3 at an electron temperature of log T e = 5.4, corresponding to the maximum abundance of Mg V. Fractional level populations and relative spectral line intensities are also calculated. Our calculated intensities are compared with the active region observations from the solar EUV rocket telescope and spectrograph (SERTS) and the diagnostic properties of Mg V are discussed. This dataset will be made available in the next version of the CHIANTI database.

Extreme‐Ultraviolet Emission Lines of Sxiiin Solar Active Region and Flare Spectra

New -matrix calculations of electron impact excitation rates for transitions among the 2s22p, 2s2p2 and 2p3 levels of S XII are presented. These data are subsequently used to derive the theoretical electron density diagnostic emission line intensity ratios R1 = I(215.16 A)/I(299.50 A), R2 = I(218.19 A)/I(299.50 A), R3 = I(288.40 A)/I(299.50 A), and R4 = I(221.41 A)/I(299.50 A). A comparison of these with observational data for solar active regions and flares, obtained with the Naval Research Laboratory's S082A spectrograph on board Skylab and the Solar EUV Rocket Telescope and Spectrograph (SERTS), reveals that the electron densities determined from R1, R3, and R4 are consistent with each other. In addition, the densities deduced from these ratios are in good agreement with those estimated from diagnostic lines in Fe XIV or Fe XV, which are formed at similar electron temperatures to S XII. However, the R2 ratios in the flare observations imply densities smaller than those from Fe XIV/Fe XV, although the active region measurements do not show such discrepancies, suggesting that the 218.19 A line may be blended with a transition from a high-temperature ion. An emission feature in the SERTS active region spectrum at 215.29 A, previously identified as the 2s2p 3P2-2s3s 3S1 transition in O V, may be due primarily to the S XII 215.16 A line.

A comparison of theoretical MgVI emission line strengths with active-region observations from serts

R-matrix calculations of electron impact excitation rates in N-like Mg vi are used to derive theoretical electron-density-sensitive emission line ratios involving 2s 22p 3−2s2p 4transitions in the 269–403 A wavelength range. A comparison of these with observations of a solar active region, obtained during the 1989 flight of the Solar EUV Rocket Telescope and Spectrograph (SERTS), reveals good agreement between theory and observation for the 2s 22p 3 4 S−2s2p 4 4 Ptransitions at 399.28, 400.67, and 403.30 A, and the 2s 22p 3 2 P−2s2p 4 2 Dlines at 387.77 and 387.97 A. However, intensities for the other lines attributed to Mg vi in this spectrum by various authors do not match the present theoretical predictions. We argue that these discrepancies are not due to errors in the adopted atomic data, as previously suggested, but rather to observational uncertainties or mis-identifications. Some of the features previously identified as Mg vi lines in the SERTS spectrum, such as 291.36 and 293.15 A, are judged to be noise, while others (including 349.16 A) appear to be blended.

Huge Coronal Structure and Heating Constraints Determined from SERTS Observations

Intensities of the Extreme-ultraviolet (EUV) spectral lines were measured as a function of radius off the solar limb by two flights of the Goddard's Solar Extreme-ultraviolet Rocket Telescope and Spectrograph (SERTS) for three quiet sun regions. Density scale heights were determined for the different spectral lines. Limits on the filling factor were determined. In the one case where an upper limit was determined it was much less than unity. Coronal heating above 1.15 solar radii is required for all three regions studied. For reasonable filling factors, local heating is needed.

Si X emission lines in spectra obtained with the Solar EUV Rocket Telescope and Spectrograph (SERTS)

New R-matrix calculations of electron impact excitation rates for transitions among the 2s22p, 2s2p2 and 2p3 levels of Si x are presented. These data are subsequently used, in conjunction with recent estimates for proton excitation rates, to derive theoretical electron density sensitive emission-line ratios involving transitions in the ∼253–356 A wavelength range. A comparision of these with observations of a solar active region and subflare, obtained during the 1989 flight of the Solar EUV Rocket Telescope and Spectrograph (SERTS), reveals that the electron densities determined from most of the Si x line ratios are consistent with one another for both solar features. In addition, the derived densities are also in good agreement with the values of Ne estimated from diagnostic lines in other species formed at similar electron temperatures to Si x, such as Fe xii and Fe xiii. These results provide observational support for the general accuracy of the adopted atomic data, and hence line ratio calculations, employed in the present analysis. However, we find that the Si x 256.32-A line is blended with the He ii transition at the same wavelength, while the feature at 292.25 A is not due to Si x, but currently remains unidentified. The intensity of the 253.81-A line in the SERTS active region spectrum is about a factor of 3 larger than expected from theory, but the reason for this is unclear, and requires additional observations to explain the discrepancy.

The Role of Velocity Redistribution in Enhancing the Intensity of the Heii304 A Line in the Quiet‐Sun Spectrum

We present observational evidence of the effect of small scale (microturbulent) velocities in enhancing the intensity of the He II lambda304 line with respect to other transition region emission lines, a process we call redistribution. We first show results from the 1991 and 1993 flights of SERTS (Solar EUV Rocket Telescope and Spectrograph). The spectral resolution of the SERTS instrument was sufficient to infer that, at the spatial resolution of 5, the line profile is nearly gaussian both in the quiet Sun and in active regions. We were then able to determine, for the quiet Sun, a lower limit for the amplitude of non-thermal motions in the region of formation of the 304 A line of the order of 10 km/s. We estimated that, in the presence of the steep temperature gradients of the solar Transition Region (TR), velocities of this magnitude can significantly enhance the intensity of that line, thus at least helping to bridge the gap between calculated and observed values. We also estimated the functional dependence of such an enhancement on the relevant parameters (non-thermal velocities, temperature gradient, and pressure). We then present results from a coordinated campaign, using SOHO/CDS and H-alpha spectroheliograms from Coimbra Observatory, aimed at determining the relationship between regions of enhanced helium emission and chromospheric velocity fields and transition region emission in the quiescent atmosphere. Using these data, we examined the behavior of the He II lambda304 line in the quiet Sun supergranular network and compared it with other TR lines, in particular with O III lambda600. We also examined the association of 304 A emission with the so-called coarse dark mottle, chromospheric structures seen in H-alpha red wing images and associated with spicules. We found that all these observations are consistent with the velocity redistribution picture.

Emission Measure Distribution for an Active Region Using Coordinated SERTS andYohkohSXT Observations

Often the derived temperature of an active region re—ects the method and the nature of the instrument used in its measurement. The emission measure (i.e., the amount of emitting material) derived from spec- troscopic observations usually depends on assumptions about the absolute elemental abundances and ionization fractions of the emitting ions. Yet establishing the distribution of emission measure with tem- perature is the —rst step needed to proceed with most of the interesting physics of active regions¨ including heating processes, cooling timescales, and loop stability. Accurately characterizing the thermal distribution of the coronal plasma requires data which can resolve multithermal features and constrain both low- and high-temperature emission. To model the temperature distribution of NOAA Active Region 7563, we have combined broadband —lter data from the Yohkoh Soft X-Ray Telescope (SXT) with simultaneous spectral line data from the Goddard Solar EUV Rocket Telescope and Spectrograph (SERTS) taken during its —ight on 1993 August 17. We have used a forward-folding technique to deter- mine the emission measure distribution of the active region loops. We have found that (1) the SXT response functions are sensitive to both the elemental abundances and the ionization fractions assumed to compute the solar spectrum that is folded through the instrument eUective area; (2) the relative cali- bration between the SERTS and the SXT instruments must be adjusted by a factor of 2 (a value consis- tent with the absolute measurement uncertainty of the 1993 SERTS —ight) no matter which abundances or iron ionization fractions are used; (3) the two-peaked diUerential emission measure previously deter- mined using SERTS data alone is not consistent with the SXT data: including the SXT data as a high- temperature constraint in the analysis requires that the emission above about 3 MK drop oU steeply rather than extending out to 6 MK. The sensitivity of the SXT —lter response functions to elemental abundance and iron ionization fraction could have a major impact on many routine analyses of SXT data. The emission measures can be greatly aUected (up to a factor of 7) and temperatures derived from —lter ratios can be signi—cantly altered (up to at least 40%) by adopting diUerent sets of commonly used elemental and ionic abundances. The results of our multithermal analysis imply that using broadband SXT data or a comparable high-temperature constraint in conjunction with high-resolution spectra covering a wide lower temperature range to study solar active regions can signi—cantly improve the information derived from either data set alone. In this study, the revised multithermal distribution reduces the thermal energy content of the region by about a factor of 2 and the required heating by about a factor of 5, which in turn relaxes some constraints on possible heating models. Subject headings: Sun: activitySun: X-rays, gamma rays

Fe xii emission lines in solar active regions observed by the RES-C spectroheliograph on the CORONAS-I mission

Theoretical line intensity ratios involving Fe xii transitions in the 186–201 Å wavelength range are compared with observational data for five solar active regions, obtained by the RES-C spectroheliograph on the CORONAS-I mission. Generally good agreement is found between theory and observation, hence resolving discrepancies previously found in the comparison of calculations with active region and subflare spectra from the Solar EUV Rocket Telescope and Spectrograph (SERTS). However, the Fe xii 190.06- and 201.12-Å lines are blended with Fe x 190.04 Å and Fe xiii 201.13 Å, respectively. In addition, a weak feature at ∼197 Å, tentatively identified as Fe xii 196.87 Å, does not appear to be due to this ion.

Using Strong Solar Coronal Emission Lines as Coronal Flux Proxies

We investigate the possibility that strong EUV lines observed with the Goddard Solar EUV Rocket Telescope and Spectrograph (SERTS) provide good proxies for estimating the total coronal flux over shorter wavelength ranges. We use coordinated SERTS and Yohkoh observations to obtain both polynomial and power-law fits relating the broad-band soft X-ray fluxes to the intensities of Fexvi 335 U and 361 U, Fexv 284 U and 417 U, and Mgix 368 U measured with SERTS. We found that the power-law fits best cover the full range of solar conditions from quiet Sun through active region, though not surprisingly the ‘cooler’ Mgix 368 U line proves to be a poor proxy. The quadratic polynomial fits yield fair agreement over a large range for all but the Mgix line. However, the linear fits fail conspicuously when extrapolated into the quiet-Sun regime. The implications of this work for the Heii 304 U line formation problem are also briefly considered.

Spectral Diagnostics of an Active Region Observed by the Solar EUV Rocket Telescope and Spectrograph (SERTS)

The EUV spectrum of a solar active region observed by SERTS-89 is used to estimate physical parameters such as electron density, elemental abundance and inhomogeneity in the emitting source. A total of 13 ions, namely, Neiv-vi, Mgv-ix, Sivii-x and Sx, are studied in the SERTS spectral range 170-450 U, providing plasma diagnostics at temperatures between105 –106 K. Attention is called to results derived from ion pairs of different elements that are formed over similar temperature regimes, which allow special checks on the standard assumptions of spectral analyses. Some EUV lines, not originally reported in the SERTS-89 spectrum, are shown to have measureable intensities and are indicated for future observations.

Relative Elemental Abundances of the Quiet Solar Corona as Determined by SERTS

Intensities of extreme-ultraviolet (EUV) spectral lines were measured as a function of radius off the solar limb by two flights (1989 May 5 and 1991 May 7) of the Solar Extreme-ultraviolet Rocket Telescope and Spectrograph (SERTS) for three quiet solar regions. The line-ratio density, line-ratio temperature, and emission measure were determined. The relative abundances of silicon, aluminum, and chromium to iron were determined. Results agreed with standard coronal relative elemental abundances for one observation, but did not agree for the other, in which aluminum was overabundant.

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).

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.

The structure of the solar corona as observed by the Solar Extreme ultraviolet Rocket Telescope and Spectrograph

Data from the Solar Extreme-ultraviolet Rocket Telescope and Spectrograph (SERTS) have been used to address a number of important scientific problems. The primary strength of the SERTS data is the fact that this spectral range is rich with emission lines. Over 270 lines are seen in the SERTS active Sun spectrum, from 57 different ions. For example, multiple (≥4) lines are observed for all ionization states of iron from Fe IX to Fe XVII. Temperatures and densities have been derived for a number of active and quiet Sun regions, the coronal magnetic field strength has been estimated for both a plage region and an active region.

Emission Lines of NI XVIII in the Solar EUV Spectrum

Using electron excitation rates calculated with the R-matrix code, theoretical Nixviii electron-temperature-sensitive emission line ratios are presented for R 1 = I(220.41 A)/I(320.56 A) , R 2 = I(233.79 A)/I(320.56 A) , and R 3 = I(220.41 A)/I(292.00 A) . A comparison of these with observational data for two solar flares, obtained by the Naval Research Laboratory's S082A slitless spectrograph on board Skylab, reveals good agreement between theory and observation for R 1 and R 2 in two spectra, which provides limited support for the accuracy of the atomic data adopted in the analysis. However, several of the measured ratios are much larger than theory predicts, which is probably due mainly to saturation of the strong 292.00 and 320.56 A lines on the photographic film used to record the S082A data. A comparison of our line ratio calculations with active region observations made by the Solar EUV Rocket Telescope and Spectrograph (SERTS) indicate that a feature at 236.335 A, identified as the Nixviii 3p 2 P 3/2 - 3d 2 D 3/2 transition in the SERTS data, is actually the Arxiii 2s 22p 2 3 P 0 - 2s2p 3 3 D 1 line. The potential usefulness of the Nixviii line ratios as electron temperature diagnostics for the solar corona is briefy discussed.

Measuring Active and Quiet-Sun Coronal Plasma Properties with Extreme-Ultraviolet Spectra from SERTS

view Abstract Citations (166) References (65) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Measuring Active and Quiet-Sun Coronal Plasma Properties with Extreme-Ultraviolet Spectra from SERTS Brosius, Jeffrey W. ; Davila, Joseph M. ; Thomas, Roger J. ; Monsignori-Fossi, Brunella C. Abstract We obtained high-resolution extreme-ultraviolet (EUV) spectra of solar active regions, quiet-Sun areas, and off-limb areas during 1991 May 7 and 1993 August 17 flights of NASA/Goddard Space Flight Center's Solar EUV Rocket Telescope and Spectrograph (SERTS). The 1991 flight was the first time a multilayer coated diffraction grating was ever used in space. Emission lines from the eight ionization stages of iron between Fe+9 (Fe x) and Fe+16 (Fe XVII) were observed. Values of numerous density- and temperature-insensitive line intensity ratios agree with their corresponding theoretical values. Intensity ratios among various lines originating in a common stage of ionization provide measurements of coronal electron density. Numerous density-sensitive ratios are available for Fe xiii, and they yield active region density (cm-3) logarithms of 9.66±0.49 and 9.60±0.54 for the 1993 and 1991 flights, respectively, and a quiet-Sun density of 9.03±0.28 for the 1993 flight. Filling factors, calculated from the derived densities assuming a path length of 1 × 109 cm, range from several thousandths to nearly unity. Intensity ratios among lines originating in different ionization stages of iron yield measurements of coronal electron temperature in the isothermal approximation. The line ratios yield temperatures ranging from 1.1 × 106 to 5.2 × 106 K for the active regions, and 1.0 × 106 to 2.1 × 106 K for the quiet Sun, depending upon the ionization stages used. The derived temperature diminishes with decreasing ionization stages. Fe XVII emission, detected in the active regions but not in the quiet areas, accounts for the higher maximum active region temperature. Derived active region temperatures are greater than their quiet-Sun counterparts for ratios that include lines from Fe xiv through Fe XVI; however, the derived active region and quiet-Sun temperatures are not statistically significantly different for line intensity ratios that involve only Fe x through Fe xiii. The latter similarity in derived temperatures suggests the presence of similar thermal structures in all the areas observed, although the active regions also harbor hotter material. Differential emission measure (DEM) distributions were constructed for the active region and quiet- Sun observations obtained during both flights. The two quiet-Sun DEM curves and the 1993 active region DEM curve all show peaks between log T = 6.1 and 6.2. The 1993 active region DEM has a second peak between log T = 6.6 and 6.7, and the 1991 active region DEM has only one peak, between log T = 6.5 and 6.6. Thus, the 1993 active region DEM curve appears, in some sense, to be a composite of the quiet-Sun DEM curve and the 1991 active region DEM curve. The 1991 active region exhibited flaring activity, yielded higher line ratio temperatures, and contained greater photo spheric magnetic fields than the 1993 active region. Publication: The Astrophysical Journal Supplement Series Pub Date: September 1996 DOI: 10.1086/192332 Bibcode: 1996ApJS..106..143B Keywords: SUN: ACTIVITY; SUN: CORONA; SUN: UV RADIATION full text sources ADS |

Si VII/Mg VII and Si IX/Mg IX line diagnostics for solar plasma

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.

Fe xii emission lines in spectra obtained with the Solar EUV Rocket Telescope andSpectrograph (SERTS)

Fe xii emission lines in spectra obtained with the Solar EUV Rocket Telescope andSpectrograph (SERTS)

Electron pressure in an active region observed by SERTS

The electron pressure in the active region AR 5464, at S18 W45, has been studied with the help of emission lines from the Si VIII ion observed by the Solar EUV Rocket Telescope and Spectrograph (SERTS) on 5 May 1989. The EUV line emissivity ratios have been computed as a function of electron density and also at an appropriate electron pressure in the emitting region. The electron pressure in the active region, from theoretical line ratio curves and with the help of the SERTS observation, is discussed.

Solar EUV Rocket Telescope and Spectrograph (SERTS) Observations of Fe XII Emission Lines

Abstract.Theoretical electron density sensitive emission line ratios involving transitions in the 186–383 Å wavelength range are compared with observational data for a solar active region and a subflare, obtained by the Solar EUV Rocket Telescope and Spectrograph (SERTS). Electron densities derived from the majority of the ratios are consistent with one another, and are also in good agreement with the values of density estimated from diagnostic lines in other species formed at similar temperatures to Fe XII. These results provide observational support for the general accuracy of the diagnostic calculations. In addition, our analysis indicates that a line at 283.70 Å in the active region spectrum is the 3s23p32D3/2−3s3p42P1/2 transition in Fe XII, the first time (to the best of our knowledge) that this line has been identified in the solar spectrum. Several of the line ratios considered are predicted to be relatively insensitive to the adopted electron temperature and density, and the generally good agreement found between theory and observation for these provides evidence for the reliability of the SERTS instrument calibration. The application of the Fe XII diagnostics to EUVE observations of the F5 subgiant Procyon is briefly discussed.