Si Ix Research Articles

Shockingly Bright Warm Carbon Monoxide Molecular Features in the Supernova Remnant Cassiopeia A Revealed by JWST

We present JWST NIRCam (F356W and F444W filters) and MIRI (F770W) images and NIRSpec Integral Field Unit (IFU) spectroscopy of the young Galactic supernova remnant Cassiopeia A (Cas A) to probe the physical conditions for molecular CO formation and destruction in supernova ejecta. We obtained the data as part of a JWST survey of Cas A. The NIRCam and MIRI images map the spatial distributions of synchrotron radiation, Ar-rich ejecta, and CO on both large and small scales, revealing remarkably complex structures. The CO emission is stronger at the outer layers than the Ar ejecta, which indicates the re-formation of CO molecules behind the reverse shock. NIRSpec-IFU spectra (3–5.5 μm) were obtained toward two representative knots in the NE and S fields that show very different nucleosynthesis characteristics. Both regions are dominated by the bright fundamental rovibrational band of CO in the two R and P branches, with strong [Ar vi] and relatively weaker, variable strength ejecta lines of [Si ix], [Ca iv], [Ca v], and [Mg iv]. The NIRSpec-IFU data resolve individual ejecta knots and filaments spatially and in velocity space. The fundamental CO band in the JWST spectra reveals unique shapes of CO, showing a few tens of sinusoidal patterns of rovibrational lines with pseudocontinuum underneath, which is attributed to the high-velocity widths of CO lines. Our results with LTE modeling of CO emission indicate a temperature of ∼1080 K and provide unique insight into the correlations between dust, molecules, and highly ionized ejecta in supernovae and have strong ramifications for modeling dust formation that is led by CO cooling in the early Universe.

First Infrared Coronal Spectra from DKIST/Cryo-NIRSP: Comparisons with Global MHD Models

The Cryogenic Near-Infrared Spectropolarimeter (Cryo-NIRSP) is now conducting science operations at the National Science Foundation’s Daniel K. Inouye Solar Telescope (DKIST). We report results obtained during instrument commissioning that advance multiwavelength coronagraphic observations in the infrared. This includes the first observations of the Fe xiii 1075 nm, Fe xiii 1079 nm, Si x 1430 nm, and Si ix 3934 nm forbidden lines. The Si ix observations, in particular, significantly improve upon the few previous ground-based detections and open up this diagnostic for more routine study. We analyse long-slit spectra in each line sampling elongations from 1.06 to 1.52 solar radii above the northeast solar limb on 2022 February 14. Line characteristics as a function of radial distance are derived and discussed in comparison to modeled emission emergent from global coronal magnetohydrodynamic models with different heating prescriptions. We find favorable correspondence between the observations and different aspects of these models, and further demonstrate the utility of infrared observations for constraining coronal models. Continued DKIST/Cryo-NIRSP observations including polarimetric data, together with ongoing improvements in data calibrations, promise significant value for coronal studies.

The Airborne Infrared Spectrometer: Development, Characterization, and the 2017 August 21 Eclipse Observation

On 2017 August 21, the Airborne Infrared Spectrometer (AIR-Spec) observed the total solar eclipse at an altitude of 14 km from aboard the NSF/NCAR Gulfstream V research aircraft. The instrument successfully observed the five coronal emission lines that it was designed to measure: Si x 1.431 μm, S xi 1.921 μm, Fe ix 2.853 μm, Mg viii 3.028 μm, and Si ix 3.935 μm. Characterizing these magnetically sensitive emission lines is an important first step in designing future instruments to monitor the coronal magnetic field, which drives space weather events, as well as coronal heating, structure, and dynamics. The AIR-Spec instrument includes an image stabilization system, feed telescope, grating spectrometer, and slit-jaw imager. This paper details the instrument design, optical alignment method, image processing, and data calibration approach. The eclipse observations are described and the available data are summarized.

A Spectroscopic Survey of Infrared 1–4 μm Spectra in Regions of Prominent Solar Coronal Emission Lines of Fe XIII, Si X, and Si IX

The infrared solar spectrum contains a wealth of physical data about the Sun and is being explored using modern detectors and technology with new ground-based solar telescopes. One such instrument will be the ground-based Cryogenic Near-IR Spectro-Polarimeter of the Daniel K. Inouye Solar Telescope (DKIST), which will be capable of sensitive imaging of the faint infrared solar coronal spectra with full Stokes I, Q, U, and V polarization states. Highly ionized magnetic dipole emission lines have been observed in galaxies and the solar corona. Quantifying the accuracy of spectral inversion procedures requires a precise spectroscopic calibration of observations. A careful interpretation of the spectra around prominent magnetic dipole lines is essential for deriving physical parameters and particularly for quantifying the off-limb solar coronal observations from DKIST. In this work, we aim to provide an analysis of the spectral regions around the infrared coronal emission lines of Fe xiii 1074.68 nm, Fe xiii 1079.79 nm, Si x 1430.10 nm, and Si ix 3934.34 nm, aligning with the goal of identifying solar photospheric and telluric lines that will help facilitate production of reliable inversions and data products from four sets of solar coronal observations. The outputs can be integrated in processing pipelines to produce level 2 science-ready data.

Atomic structure for carbon-like ions from Na vi to Ar xiii

ABSTRACT We have calculated the energy levels, oscillator strengths, and transition probabilities for eight carbon-like ions (Na vi, Mg vii, Al viii, Si ix, P x, S xi, Cl xii and Ar xiii) using the Hartree–Fock pseudo-relativistic (HFR) and Thomas–Fermi–Dirac–Amaldi (TFDA) approaches. We used configuration expansions containing eight configurations, namely 2s2 2p2, 2s 2p3, 2s2 2p 3s, 2s2 2p 3p, 2s2 2p 3d, 2s2 2p 4s, 2s2 2p 4p, and 2s2 2p 5s. For each of the considered ions we obtained 59 energy levels, a number of which are not in the National Institute of Standards and Technology (NIST) data base. We compared our results with critically selected experimental data from NIST and with calculations made using the multiconfiguration Hartree–Fock (MCHF) method. We calculated weighted oscillator strengths and transition probabilities using two methods (HFR and TFDA) for the 2s2 2p2 and 2s 2p3 configurations for the eight C-like ions considered here. We analysed the atomic structure parameter trends, which allowed us to find missing data belonging to an isoelectronic sequence. The energy levels, oscillator strengths, and transition probabilities calculated here are in good agreement with the data from the NIST data base. Because emission and absorption features from C-like ions are often used for density and temperature diagnostics of various plasmas in astrophysics, and in studies of the solar corona, including solar flares, and of the coronae of other stars and of ionized outflows in active galactic nuclei etc., the obtained data will be useful for improving plasma diagnostics and modelling, in particular for the X-ray Universe.

Forward Synthesis of Polarized Emission in Target DKIST Coronal Lines Applied to 3D MURaM Coronal Simulations

Self-consistent magnetohydrodynamic simulations of the solar corona with fine ( $\lesssim10$ km) grid scales are now being realized in parallel to advancements in high-resolution coronal spectropolarimetry provided by the National Science Foundation’s Daniel K. Inouye Solar Telescope (DKIST). We investigate the synthesis of polarized emission in the presence of apparent coronal fine structure exhibited by 3D MURaM coronal simulations for the key polarized spectral lines targeted by DKIST, namely Fe xiv $\lambda5303$ , Fe xi $\lambda7892$ , Fe xiii $\lambda10746$ , Fe xiii $\lambda10798$ , Si x $\lambda14301$ , and Si ix $\lambda39343$ . To benchmark our calculations, we provide detailed comparisons between the employed polarized line formation theory and established scalar line synthesis tools provided by the Chianti database team. To accelerate polarized synthesis for large simulations, we create efficient lookup tables based on atomic models significantly larger than previous studies. The spectral data cubes we describe provide a useful guide for the new era of multi-spectral DKIST coronal diagnostics as we discuss specific analysis techniques and challenges.

K-shell energy levels and radiative rates for transitions in Si ix

K-shell energy levels and radiative rates for transitions in Si ix

Si IX Emission Lines in Spectra Obtained with the Solar euv Research Telescope and Spectrograph (Serts)

Theoretical electron-density-sensitive emission line ratios involving 2s22p2–2s2p3 transitions in Si ix between 223 and 350 A are presented. A comparison of these with an extensive dataset of solar-active-region, quiet-Sun, subflare and off-limb observations, obtained during rocket flights by the Solar EUV Research Telescope and Spectrograph (SERTS), reveals generally very good agreement between theory and experiment. This provides support for the accuracy of the line-ratio diagnostics, and hence the atomic data on which they are based. In particular, the density-sensitive intensity ratio I(258.10 A)/I(349.87 A) offers an especially promising diagnostic for studies of coronal plasmas, as it involves two reasonably strong emission lines and varies by more than an order of magnitude over the useful density range of 109–1011 cm−3. The 2s22p2 1S0–2s2p3 1P1 transition at 259.77 A is very marginally identified for the first time in the SERTS database, although it has previously been detected in solar flare observations.

Spectroscopic Detection of the 3.934 Micron Line of S[CLC]i[/CLC] [CSC]ix[/CSC] in the Solar Corona

We report the detection of the line of Si ix using the McMath-Pierce telescope on Kitt Peak. 22 3 2s 2 pP 1 r 0 Observations were made of the solar disk and at various heights above the limb between 2002 May 13 and 17, under nonideal sky conditions, using the 13.5 m vertical spectrograph and an InSb single-diode detector. We report a new rest wavelength for the line and discuss its potential use as a diagnostic of coronal magnetic fields using ground-based telescopes. Our observations give mm, consistent with earlier less accurate l p 3.93434 0.00007 rest values, but it places the blue wing of the line under a strong telluric line. In the active regions observed, the NO 2 line’s intensity is comparable to or larger than predicted in earlier work for the quiet Sun. Subject headings: Sun: corona — Sun: infrared

The coronal line regions of planetary nebulae NGC 6302 and 6537: 3-13 m grating and echelle spectroscopy

We report on advances in the study of the cores of NGC 6302 and 6537 using infrared grating and echelle spectroscopy. In NGC 6302, emission lines from species spanning a large range of ionization potential, and in particular [Si ix] 3.934 μm, are interpreted using photoionization models (including cloudy), which allow us to re-estimate the temperature of the central star to be about 250 000 K. All of the detected lines are consistent with this value, except for [Al v] and [Al vi]. Aluminium is found to be depleted to one hundredth of the solar abundance, which provides further evidence for some dust being mixed with the highly ionized gas (with photons harder than 154 eV). A similar depletion pattern is observed in NGC 6537. Echelle spectroscopy of IR coronal ions in NGC 6302 reveals a stratified structure in ionization potential, which confirms photoionization to be the dominant ionization mechanism. The lines are narrow (<22 km s−1 FWHM), with no evidence of the broad wings found in optical lines from species with similar ionization potentials, such as [Ne v] 3426 Å. We note the absence of a hot bubble, or a wind-blown bipolar cavity filled with a hot plasma, at least on 1 arcsec and 10 km s−1 scales. The systemic heliocentric velocities for NGC 6302 and 6537, measured from the echelle spectra of IR recombination lines, are found to be −34.8±1 km s−1 and −17.8±3 km s−1. We also provide accurate new wavelengths for several of the infrared coronal lines observed with the echelle.

Electron densities above a polar coronal hole based on improved Si IX density diagnostics

Using new close-coupling excitation rates for the C-like ion Si ix, density-diagnostic ratios based on Si ix lines have been re-evaluated and applied to a sequence of CDS observations taken above a polar coronal hole. The derived electron densities are in excellent agreement with previous values of Neestimated from the N-like ion Si viii for another coronal hole. The confirmed trend is for a fall-off of one order of magnitude within the first 0.3 R⊙above the limb. These densities are well fitted with an analytic formula for the density profile out to at least 8 R⊙, by which stage the electron density has fallen to ∼4×103 cm−3, from 1.5×108 cm−3at 1.0 R⊙.

Unified treatment of electron-ion recombination in the close-coupling approximation.

A unified treatment for electron-ion recombination has been developed and applied to detailed calculations for cross sections and total recombination rate coefficients for a number of atoms and ions. The ab initio calculations are carried out in the close-coupling approximation employing the R-matrix method for the bound and the continuum states of the electron-ion system. All final states of the recombined system are taken into account and the present method subsumes both the radiative and the dielectronic recombination (RR and DR) processes over all energy and temperature ranges of practical importance. Recombined states of the electron-ion system are divided into two groups: (a) n\ensuremath{\le}${\mathit{n}}_{0}$ and (b) ${\mathit{n}}_{0}$n\ensuremath{\le}\ensuremath{\infty}. Photoionization cross sections are calculated for all bound states of group (a), typically a few hundred bound states, referred to as low-n states, including a detailed energy resolution of the several infinite series of autoionizing resonances converging onto the various excited states of the core ion included in the close-coupling expansion. High-n states of group (b) are treated primarily through the theory of DR developed by Bell and Seaton [J. Phys. B 18, 1589 (1985)]. DR collision strengths with detailed resonance structures are presented.The detailed and the resonance-averaged DR collision strengths show characteristic peaks at the target thresholds of the core ion corresponding to dipole-allowed transitions. Individual bound states of the e+ion system with dominant contribution to low-energy recombination are described. The present results demonstrate the importance of (i) recombinations to excited states (particularly the metastable states), and (ii) low-energy autoionizing resonances, both of which result in large contributions to effective electron-ion recombination. The individual contributions of the excited bound states of the e+ion system are calculated and their relative contribution to the total are discussed. The general pattern of the recombination rate, as a function of electron temperature, is studied along an isoelectronic sequence. It is found that while the low-energy (temperature) recombination increases with ion charge z, the relative high-energy (temperature) contribution to the total decreases; i.e., viewed as independent processes, the RR part increases while the DR decreases with z. Total recombination rate coefficients for several atoms and ions (C ii, S ii, C ii, N ii, O iii, F iv, Ne v, and Si ix) are obtained over the entire temperature range of possible interest in applications. Comparisons are made with earlier works on RR and DR.

Satellites to Delta n = 1 transitions between high-lying levels of multiply ionized atoms.

In a \ensuremath{\theta} pinch discharge satellites to \ensuremath{\Delta}n=1 transitions between high-lying levels are observed for the ions Si ix, Si x, and Si xi, but not for Si xii. They are identified as \ensuremath{\Delta}n=1 transitions between the corresponding levels of doubly excited systems. At high densities, the series of Rydberg levels above their respective thermal limit are collisionally coupled to their ionization limit: The intensity ratio of a transition to that of its satellite thus offers the unique possibility of measuring the ratio of the population density in the ground energy level of the next ionization stage to that in the lowest excited levels of this ion.

Mg vii and Si ix line ratios in the sun

Recent R-matrix calculations of electron excitation rates for Mg vii and Si ix are used to determine the theoretical density sensitive emission line ratios R1= I(2s2p31D0 - 2s22p21D e )/I(2s2p33S0 - 2s22p23P 2 e ) and R2= I(2s2p31P0 - 2s22p21D e )/I(2s2p33S0 - 2s22p23P 2 e ). These are found to be quite similar to the earlier results of Mason and Bhatia. Electron densities derived using observed R1 and R 2 ratios from Skylab NRL XUV spectra of solar flares and active regions are in good agreement, and compare favourably with those deduced from ions formed at similar electron temperatures to Mg vii and Si ix.

Enhancement of the solar X-ray line intensities due to dielectronic recombination as an excitation process

Intensities of resonance lines in X-ray region for Si ix–Si xiv ions are calculated by considering total excitation, i.e., excitation due to electron impact and dielectronic recombination. It is found that the contribution of the latter is quite significant. For consistency, the electron density effect in our calculations is not only accounted for in the ionization equilibrium but also in the total rate of excitation. It is also found that the contribution of electron density effect is pronounced with the inclusion of dielectronic recombination as an excitation mechanism. The computed average line intensities are compared with the available observations and a table of line flux for various wavelengths of the above-mentioned ions at different temperatures is also given.

Analysis of EUV Observations of a Coronal Active Region Made During the 7 March 1970 Eclipse

(Monthly Notices Roy. Astron. Soc.). Rocket observations of the EUV solar spectrum obtained during the total eclipse of 7 March 1970 showed the presence of a large coronal condensation on the NE limb (Gabriel et al., 1971). The condensation shows the existence of loop structure, which defines the local magnetic fields, and is apparent in forbidden lines including those of Si viii, Si ix, S xi, Fe ix, Fe xi and Fe xii which lie between 1200 Å and 2050 Å (Jordan, 1971). These lines are formed in the temperature range 9.3 × 105K to 2.0 × 106K. The photographic observations of the active region show clearly that the spatial distribution of material varies considerably with its temperature.

Infrared Lines of the Solar Corona. I. Prediction

view Abstract Citations (10) References (8) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Infrared Lines of the Solar Corona. I. Prediction Münch, Guido Abstract The existence of coronal lines in the instrumental infrared, due to the ions Mg7+, Al8+, and 5i8+ and Si +, is predicted and their intensities are estimated. The possibility of detecting these lines with practicable infrared spectrometers and photoconductive detectors is analyzed, taking into consideration attenuation by atmospheric gases. The powers radiated in the [Mg viiij, [Si ix], and [Si x] lines are found to be large enough to make their detection feasible with instruments of modest size. Publication: The Astrophysical Journal Pub Date: July 1966 DOI: 10.1086/148758 Bibcode: 1966ApJ...145..237M full text sources ADS |