Ca XVI Research Articles

Total and state-specific electron-ion recombination rates and photoionization of Ca XV for high temperature plasma

The inverse processes of photoionization and electron-ion recombination of (Ca XV + hν↔ Ca XVI + e), are studied using the unified method of Nahar and Pradhan for a large number of bound states, 582 in total with n≤10 and l≤9, for their characteristic features particularly in the high energy region that can impact plasmas at high temperature. The unified method which implements close-coupling (CC) approximation and the R-matrix method includes both the radiative recombination (RR) and dielectronic recombination (DR) for the total recombination and yields self-consistent sets of results for both the inverse processes. The present study, carried out in large scale computations, employs a large CC wavefunction expansion of 29 LS states belonging to n=2,3 complexes of the core ion Ca XVI, and appeared to be the first detailed study for the electron-ion recombination of the ion. The present results include (i) state-specific photoionization cross sections (σPI(nLS)) leaving the core ion in the ground state, (ii) state-specific recombination rate coefficients (αRC(nLS,T)) that include both the RR and DR, (iii) total recombination rate coefficients (αRC) with temperature that include contributions of infinite number of recombined states, and (iv) a spectrum of total electron-ion recombination cross sections and rates with respect to photoelectron energy. The study finds that the core ion excitations from the ground to high n=3 states have introduced Rydberg resonances which are stronger and Seaton resonances which are more enhanced in the high energy region of σPI compared to those introduced by excitations to the n=2 states. Such features have contributed to the shape of the temperature dependent state-specific αRC(nLS,T), and have resulted in three DR bumps/ shoulders in the high temperature region of the total αRC(T) where the third DR bump at temperature of ∼ 4 MK has raised αRC(T) at high T above all previous rates. The results are expected to be accurate within 10%–15% and provide more complete and precise spectral modelings for the high temperature plasmas where the highly charged Ca XV is more abundant.

Highly Ionized Calcium and Argon X-Ray Spectra from a Large Solar Flare

Abstract X-ray lines of helium-like calcium (Ca xix) between 3.17 and 3.21 Å and associated Ca xviii dielectronic satellites have previously been observed in solar flare spectra, and their excitation mechanisms are well established. Dielectronic satellites of lower-ionization stages (Ca xvii–Ca xv) are not as well characterized. Several spectra during a large solar flare in 2001 by the DIOGENESS X-ray spectrometer on the CORONAS-F spacecraft show the Ca xvii and Ca xvi satellites, as well as lines of ionized argon (Ar xvii, Ar xvi), including dielectronic satellites. The DIOGENESS spectra are compared with spectra from a synthesis code developed here based on an isothermal assumption with various atomic sources including dielectronic satellite data from the Cowan Hartree–Fock code. Best-fit comparisons are made by varying the temperature as the code’s input (Ar/Ca abundance ratio fixed at 0.33); close agreement is achieved, although with adjustments to some ion fractions. The derived temperature is close to that derived from the two GOES X-ray channels, T GOES . Some lines are identified for the first time. Similar spectra from the P78-1 spacecraft and the Alcator C-Mod tokamak have also been analyzed and similar agreements were obtained. The importance of blends of calcium and argon lines is emphasized, affecting line ratios used for temperature diagnostics. This analysis will be applied to the Solar Maximum Mission Bent Crystal Spectrometer archive and to X-ray spectra expected from the ChemiX instrument on the Sun-orbiting Interhelioprobe spacecraft, while the relevance to X-ray spectra from non-solar sources is indicated.

Photoionization of Ca XV with high energy features

Photoionization cross sections of (Ca XV + hν → Ca XVI + e), with high energy resonant photo-absorption phenomena, of a large number of bound states, 701 in total with n ≤ 10 and l ≤ 9, are reported. They are obtained using the R-matrix method with a close coupling (CC) wavefunction expansion of 29 states of n = 2,3 complexes of the core ion Ca XVI. Characteristic features found in photoionization of the ion are illustrated with examples. The cross section (σPI) of the ground 2s22p2(3P) state is found to be unaffected by the size of the wavefunction expansion except for weak sparse resonances in high energy region. However, effects on excited states are considerable as the core excitations to n = 3 states are manifested in huge resonant absorption in high energy photoionization. They show existence of prominent high peak resonant features and enhancement in the background that were not studied before for Ca XV. In addition photoionization of the excited states with a single valence electron is dominated by Seaton resonant structures formed by the photo-excitation-of-core in the high energy region. These features will impact other quantities, such as the opacity, electron-ion recombination in high temperature plasmas where the ion exists, and hence will play important role in determination of elemental abundances in the astronomical objects.

Calcium‐to‐Argon and Nickel‐to‐Argon Abundance Ratios as Tracers of the Source Region of Postflare Loop System Material

Intensities of abundance diagnostic lines of Ca XV, Ca XVI, Ni XVII, Ar XIII, and Ar XV have been derived for a classic flare loop system observed during the Skylab mission. These have been used to test for photospheric or coronal origin of the flare loop material. The resulting FIP-bias factors are between 1.7 and 4.6 with a majority of the values around 4.5 indicating a source with material modified by the FIP effect. The loop system bias factors are similar to those observed in a sample of Skylab prominences, suggesting that the disrupted mass of the preflare embedded filament provided the loop system material.

Simulation of the EUV Spectrum of Ca XVI

Abstract The extreme ultraviolet (EUV) spectrum of a Boron-like Ca ion was simulated by using a relativistic multi-configuration atomic package. As compared to previous work [Keenan et al.(1998)], the present study involved indirect processes, such as collision ionization, radiative recombination, dielectronic recombination, and resonance excitation from or to Beryllium-like and Carbon-like Ca ions. The effects of these processes were using three models, named one-, two-, and three-ion. We have found that these indirect processes are important to simulate the EUV spectrum of the Boron-like Ca ion, which will affect the diagnostics of astronomical and laboratory plasmas.

Extreme Ultraviolet Emission Lines of ca xv in Solar and Laboratory Spectra

New R-matrix calculations of electron impact excitation rates in Ca xv are used to derive theoretical electron density diagnostic emission line intensity ratios involving 2s22p2–2s2p3 transitions, specifically R1=I(208.70 A)/I(200.98 A), R2=I(181.91 A)/I(200.98 A), and R3=I(215.38 A)/I(200.98 A), for a range of electron temperatures (Te=106.4–106.8 K) and densities (Ne=109–1013 cm−3) appropriate to solar coronal plasmas. Electron densities deduced from the observed values of R1, R2, and R3 for several solar flares, measured from spectra obtained with the Naval Research Laboratory's S082A spectrograph on board Skylab, are found to be consistent. In addition, the derived electron densities are in excellent agreement with those determined from line ratios in Ca xvi, which is formed at a similar electron temperature to Ca xv. These results provide some experimental verification for the accuracy of the line ratio calculations, and hence the atomic data on which they are based. A set of eight theoretical Ca xv line ratios involving 2s22p2–2s2p3 transitions in the wavelength range ∼ 140–216 A are also found to be in good agreement with those measured from spectra of the TEXT tokamak plasma, for which the electron temperature and density have been independently determined. This provides additional support for the accuracy of the theoretical line ratios and atomic data.

Extreme Ultraviolet Transitions of Caxviin Solar Flare and Laboratory Spectra

New R-matrix calculations of electron impact excitation rates for transitions among the 2s22p, 2s2p2, and 2p3 levels of Ca XVI 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 2s22p-2s2p2 transitions in the ~155-225 A wavelength range. A comparison of these with observational data for solar flares, obtained with the Naval Research Laboratory's S082A spectrograph on board Skylab, reveals excellent agreement between theory and observation. In addition, the theoretical ratios compare favorably with those measured from the TEXT tokamak plasma, for which the electron temperature and density have been independently determined. This provides experimental support for the accuracy of the atomic data, and hence line ratio calculations, employed in the present analysis.

CROSS SECTIONS AND RATE COEFFICIENTS FOR EXCITATION WITHIN THE 1s22s22p2PAND 1s22s2p2 4PMULTIPLETS IN BORON-LIKE IONS C II–Ni XXIV BY HEAVY PARTICLE IMPACT

Cross sections for excitation of the fine-structure transitions within the 1s22s22p2Poand 1s22s2p2 4Pemultiplets in boron-like ions by proton, deuteron, triton, and α-particle impact have been calculated using a close-coupled impact-parameter method, which includes the effects of dipole coupling to nearby configurations by means of a polarization potential. The ions considered are C II, N III, O IV, Ne VI, Mg VIII, Al IX, Si X, S XII, Ar XIV, Ca XVI, Ti XVIII, Cr XX, Mn XXI, Fe XXII, Co XXIII, and Ni XXIV. Excitation rate coefficients have been calculated from the cross sections for a wide range of temperatures.

Electron-impact excitation along an isoelectronic sequence: B-like ions.

A systematic study of collision strengths for the electron-impact excitation of ions along an isoelec- tronic sequence is presented. 105 excitation transitions between 15 fine-structure levels of the eight [ital LS] terms 2[ital s][sup 2]2[ital p]([sup 2][ital P][sup [ital o]]), 2[ital s]2[ital p][sup 2]([sup 4][ital P],[sup 2][ital D],[sup 2][ital S],[sup 2][ital P]), and 2[ital p][sup 3]([sup 4][ital S][sup [ital o]],[sup 2][ital D][sup [ital o]],[sup 2][ital P][sup [ital o]]) in boronlike ions are considered. The calculations include O IV, Ne VI, Mg VIII, Al IX, Si X, S XII, Ar XIV, Ca XVI, and Fe XXII in an eight-term close-coupling expansion, using the [ital R]-matrix method [H. L. Zhang, M. Graziani, and A. K. Pradhan, Astron. Astrophys. 283, 319 (1994)]. An 11-term expansion, including some [ital n]=3 states, is also carried out for Ne VI to study the effect of the coupling to higher-[ital n] complexes. The results were compared with those with a fully relativistic distorted-wave method by Zhang and Sampson [At. Data Nucl. Data Tables 56, 41 (1994)]. The study shows that the coupling effects and the resonance effects are still pronounced for highly charged ions, even up to Fe XXII. The relativistic effects, which are incorporated into themore » [ital R]-matrix calculations through the term-coupling method [W. Eissner, M. Jones, and H. Nussbaumer, Comput. Phys. Commun. 8, 270 (1974)], begin to manifest themselves for [ital Z][ge]16. This study should provide some guidelines for future [ital R]-matrix calculations for other isoelectronic sequences.« less

B I Isoelectronic Sequence: Observation of 2s2p2-2p3 Intersystem Lines in Sc XVII and Improved Measurements for CI XIII, K XV, Ca XVI, Sc XVII, and Ti XVIII

Spectra of Cl through Ti (excluding Ar) were produced with 1 GW 15 ns) pulses from a Nd-glass laser impinging on solid targets, and observed with a 10.7 m grazing incidence spectrograph. Transition arrays 2sm2pn-2sm-12pn+1 in the B I isoelectric sequence were recorded. Two intersystem transitions 2s2p2 4P-2p3 2D of Sc XVII were identified, and improved wavelength measurements of allowed lines were made for each spectrum. From a least squares fit of radial energy integrals to Sc XVII energy levels, percentage compositions of the levels were obtained.

The solar coronal X-ray spectrum from 15.4 to 23.0 A - Lines from highly ionized calcium and chromium and their usefulness as plasma diagnostics

view Abstract Citations (32) References (33) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The solar coronal X-ray spectrum from 15.4 to 23.0 A - Lines from highly ionized calcium and chromium and their usefulness as plasma diagnostics McKenzie, D. L. ; Landecker, P. B. Abstract Observations by the SOLEX experiment from the USAF P78-1 satellite are used to examine the 15.4-23.0 Å X-ray spectrum from both flaring and nonflaring solar active region plasmas. High sensitivity, attained by summing data from several successive spectral scans, enabled the detection of more than 60 lines in this wavelength region. Most of the lines expected to be strongest from Cr XV-XVL and Ca XV-XVIII were detected; those undetected were obscured by blending. In addition, a blend of two Cr XVIII lines was observed, and three Cr XVII lines are tentatively identified. Lines from higher ionization states of Cr are at shorter wavelengths and are hard to detect because of strong Fe emission. The Cr and Ca spectra are similar to those of isoelectronic species of Fe. The Cr XV 2p6 1S0-2P5 3d-1P1 (18.497 Å) line is sufficiently strong that it can be used for analysis of both flaring and nonflaring plasmas. Calculations of the collision strength from the ground state to the 2p53d1P1 level and of the Cr ionization equilibrium are needed for optimum use of this line. Theoretical data for the Ca XVI 2P1/2-3d2D3/2 line are available, but the line is too weak to be useful for analysis of nonflaring plasmas. Furthermore, the line is density-sensitive for electron density ne ≥ 1011 cm-3 but is not a good density diagnostic because no non-density-sensitive comparison line from Ca XVI is detectable. The Ca XV line flux ratio, F(2p2 3P2-2p3d3D3)/F(2p2 3P0-2p3d1) is used to estimate flare electron densities at ∼4 × 106 K. The derived densities are in rough agreement with those derived from O VII line ratios at 2 × 106 K. The coronal abundances of Cr and Ca with respect to O are estimated; we find A(Cr)/A(O) = 0.0036 ± 0.0018 and A(Ca)/A(O) = 0.015 ± 0.005. We discuss the determination of these and other abundances by the analysis of X-ray spectra. Publication: The Astrophysical Journal Pub Date: March 1982 DOI: 10.1086/159735 Bibcode: 1982ApJ...254..309M Keywords: Abundance; Plasma Diagnostics; Solar Corona; Solar Spectra; X Ray Spectra; Calcium; Chromium; Line Spectra; Metal Ions; Solar Physics full text sources ADS |

Density sensitivity of the solar EUV emission from boron-like ions

The paper investigated the level populations and the line emission arising from ions of the boron isoelectronic sequence from C II to Ca XVI. It is found that, under conditions present in the solar corona, some of these ions have pairs of emission lines having intensity ratios which are density-sensitive. The boron-like lines observed in the solar spectrum between 300 and 1350 A are analyzed, and densities for quiet and active regions, coronal holes, sunspots, and flares are derived. Some aspects of the differences in the behavior of the emission from the lithium and boron sequences are also discussed.

Rocket Observation of AR Xii-Xvi CA Xiv-Xviii and fe XIV, xv, XXIV in the Extreme-Ultraviolet Spectrum of a Solar Flare

view Abstract Citations (48) References (23) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Rocket Observation of Ar XII-XVI Ca XIV-XVIII and Fe XIV, XV, XXIV in the Extreme-Ultraviolet Spectrum of a Solar Flare Purcell, J. D. ; Widing, K. G. Abstract The lithiumlike doublets of S xiv, Ar XVI, and Ca xviii are identified in the 300-450 A region by extrapolation of solar wavelengths and term intervals in the isoelectronic sequence. A possible observation of Fe xxiv in the flare is discussed. The solar blend at 417 A involving S xiv and the Fe xv inter- system line is resolved. The singlet resonance lines of S xiii, Ar xv, and Ca xvii are also found in the flare spectrum by isoelectronic extrapolation. Ca xiv and Ca xv are identified on the basis of laboratory wavelengths. The problem of the identification of boron-like Ar xiv and Ca xvi is discussed. The weakness of argon lines relative to calcium lines in the flare is consistent with a solar abundance of argon less than calcium. An electron density of 3 >( 1010 in the flare core is estimated from the intensity ratio of the Fe xiv lines at 211 and 219 A. Publication: The Astrophysical Journal Pub Date: August 1972 DOI: 10.1086/151626 Bibcode: 1972ApJ...176..239P full text sources ADS |