- ID:
- ivo://CDS.VizieR/J/ApJ/753/18
- Title:
- Far-IR spectrum of ethylene oxide (CH_2_-O-CH_2_)
- Short Name:
- J/ApJ/753/18
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- High-resolution Fourier Transform Infrared spectroscopy (FTIR) spectra of ethylene oxide (CH_2_-O-CH_2_) have been measured in the far-infrared region using synchrotron radiation. A total of 1182 lines between 15/cm (450GHz) and 73/cm (2.2THz) were assigned, with J_max_=64, expanding upon previous studies that had recorded spectra up to 12/cm, J_max_=49. All available data were co-fitted to provide greatly improved rotational constants for the ground vibrational state that are capable of predicting transitions up to 73/cm.
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- ID:
- ivo://CDS.VizieR/J/ApJ/760/80
- Title:
- Fe^9+^ and Fe^10+^ cross-section measurements
- Short Name:
- J/ApJ/760/80
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have measured electron impact ionization from the ground state of Fe^9+^ and Fe^10+^ over the relative electron-ion collision energy ranges 200-1900eV and 250-1800eV, respectively. The ions were confined in an ion storage ring long enough for essentially all metastable levels to radiatively relax to the ground state. For single ionization, we find a number of discrepancies between the existing theoretical cross sections and our results. The calculations appear to neglect some excitation-autoionization (EA) channels, particularly from n=3 to n' excitations, which are important near threshold, and those from n=2-->3 excitations, which contribute at about 650eV. Conversely, at higher energies the calculations appear to overestimate the importance of EA channels due to excitation into levels where n>=4. The resulting experimental rate coefficients agree with the most recent theory for Fe^9+^ to within 16% and for Fe^10+^ to within 19% at temperatures where these ions are predicted to form in collisional ionization equilibrium. We have also measured double ionization of Fe^9+^ forming Fe^11+^ in the energy range 450-3000eV and found that although there is an appreciable cross section for direct double ionization, the dominant mechanism appears to be through direct ionization of an inner shell electron producing an excited state that subsequently stabilizes through autoionization.
- ID:
- ivo://CDS.VizieR/J/ApJ/767/47
- Title:
- Fe^13+^, Fe^16+^, Fe^17+^ cross-section measurements
- Short Name:
- J/ApJ/767/47
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report measurements of electron impact ionization for Fe^13+^, Fe^16+^, and Fe^17+^ over collision energies from below threshold to above 3000eV. The ions were recirculated using an ion storage ring. Data were collected after a sufficiently long time that essentially all the ions had relaxed radiatively to their ground state. For single ionization of Fe^13+^, we find that previous single pass experiments are more than 40% larger than our results. Compared to our work, the theoretical cross section recommended by Arnaud & Raymond (1992ApJ...398..394A) is more than 30% larger, while that of Dere (2007, J/A+A/466/771) is about 20% greater. Much of the discrepancy with Dere is due to the theory overestimating the contribution of excitation-autoionization via n=2 excitations. Double ionization of Fe^13+^ is dominated by direct ionization of an inner shell electron accompanied by autoionization of a second electron. Our results for single ionization of Fe^16+^ and Fe^17+^ agree with theoretical calculations to within the experimental uncertainties.
- ID:
- ivo://CDS.VizieR/J/ApJS/189/15
- Title:
- FeII emission in a sample of AGN spectra
- Short Name:
- J/ApJS/189/15
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a study of optical FeII emission in 302 active galactic nuclei (AGNs) selected from the Sloan Digital Sky Survey. We group the strongest FeII multiplets into three groups according to the lower term of the transition (b^4^F, a^6^S, and a^4^G terms). These approximately correspond to the blue, central, and red parts, respectively, of the "iron shelf" around H{beta}. We calculate an FeII template that takes into account transitions into these three terms and an additional group of lines, based on a reconstruction of the spectrum of I Zw 1. This FeII template gives a more precise fit of the FeII lines in broad-line AGNs than other templates. We extract FeII, H{alpha}, H{beta}, [OIII], and [NII] emission parameters and investigate correlations between them. We find that FeII lines probably originate in an intermediate line region. We note that the blue, red, and central parts of the iron shelf have different relative intensities in different objects. Their ratios depend on continuum luminosity, FWHM H{beta}, the velocity shift of FeII, and the H{alpha}/H{beta} flux ratio. We examine the dependence of the well-known anti-correlation between the equivalent widths of FeII and [OIII] on continuum luminosity. We find that there is a Baldwin effect for [OIII] but an inverse Baldwin effect for the FeII emission. The [OIII]/FeII ratio thus decreases with L_{lambda}5100_. Since the ratio is a major component of the Boroson & Green Eigenvector 1 (EV1), this implies a connection between the Baldwin effect and EV1 and could be connected with AGN evolution. We find that spectra are different for H{beta} FWHMs greater and less than ~3000km/s, and that there are different correlation coefficients between the parameters.
- ID:
- ivo://CDS.VizieR/J/A+A/643/A57
- Title:
- FeII-FeVIII K lines Plasma environment effects
- Short Name:
- J/A+A/643/A57
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In the framework of compact-object accretion disks, we have calculated plasma environment effects on the atomic structure and decay parameters used in the modeling of the K lines in lowly charged iron ions, namely FeII-FeVIII. We use the fully relativistic multiconfiguration Dirac-Fock (MCDF) method approximating the plasma electron-nucleus and electron-electron screenings with a time-averaged Debye-Huckel potential. Results. Modified ionization potentials, K-threshold energies, wavelengths, radiative emission rates, and Auger widths are reported for plasmas characterized by electron temperatures and densities in the ranges 10^5^-10^7^K and 10^18^-10^22^cm^-3^. In addition, we propose two universal fitting formulae to predict the IP and K-thresold lowerings in any elemental ion. We conclude that the high-resolution X-ray spectrometers onboard the future XRISM and ATHENA space missions will be able to detect the lowering of the K edges of these Fe ions due to the extreme plasma conditions occurring in accretion disks around compact objects.
- ID:
- ivo://CDS.VizieR/J/A+A/536/A74
- Title:
- FeII forbidden lines radiative transition rates
- Short Name:
- J/A+A/536/A74
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report electric quadrupole and magnetic dipole transitions among the levels belonging to 3d^6^4s, 3d^7^ and 3d^5^4s^2^ configurations of Fe II in a large scale configuration interaction (CI) calculation. The CIV3 code developed by Hibbert and coworkers is used to determine configuration interaction wave functions for these levels: for the optimisation of two different sets of orbitals based on alternative choices of the 3d function, for creating and diagonalising the Hamiltonian matrices and finally for calculating transition probabilities.
- ID:
- ivo://CDS.VizieR/J/A+A/340/300
- Title:
- Fe II oscillator strengths
- Short Name:
- J/A+A/340/300
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A sample of the agreement between experiment (recent experimental log(gf) values) and our method (orthogonal operator technique) is shown in table 1. The experimental data are taken from the critical compilation by Giridhar and Ferro (1995RMxAA..31...23G) using data from Kroll and Kock (1987A&AS...67..225K), and from most recent data by Bergeson et al. (1996ApJ...464.1044B). Eight lines in this table are indicated by * in front of the orthogonal log(gf) value: for these lines the difference between experimental value and our calculated value is >=0.2.
- ID:
- ivo://CDS.VizieR/J/ApJ/808/174
- Title:
- FeII radiative transition rates
- Short Name:
- J/ApJ/808/174
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present extensive calculations of radiative transition rates and electron impact collision strengths for FeII. The data sets involve 52 levels from the 3d^7^, 3d^6^4s, and 3d^5^4s^2^ configurations. Computations of A-values are carried out with a combination of state-of-the-art multiconfiguration approaches, namely the relativistic Hartree-Fock, Thomas-Fermi-Dirac potential, and Dirac-Fock methods, while the R-matrix plus intermediate coupling frame transformation, Breit-Pauli R-matrix, and Dirac R-matrix packages are used to obtain collision strengths. We examine the advantages and shortcomings of each of these methods, and estimate rate uncertainties from the resulting data dispersion. We proceed to construct excitation balance spectral models, and compare the predictions from each data set with observed spectra from various astronomical objects. We are thus able to establish benchmarks in the spectral modeling of [FeII] emission in the IR and optical regions as well as in the UV FeII absorption spectra. Finally, we provide diagnostic line ratios and line emissivities for emission spectroscopy as well as column densities for absorption spectroscopy.
- ID:
- ivo://CDS.VizieR/J/A+A/377/361
- Title:
- Fe II transition probabilities and loggf
- Short Name:
- J/A+A/377/361
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report measurements of the relative intensities of 81 emission lines of Fe II between 160nm and 350nm (62168cm^-1^ to 28564cm^-1^) from 4 levels by high resolution Fourier transform spectrometry, using a Penning discharge lamp as light source. These relative intensities have been used to determine the line branching fractions, which have then been combined with accurate experimental radiative lifetime measurements reported recently to give absolute transition probabilities and oscillator strengths for 81 lines. The accuracy of these f-values is compared with other previous experimental measurements, and with theoretical values. The new transition probabilities will allow accurate determinations of Fe II abundances in a wide variety of astrophysical objects.
- ID:
- ivo://CDS.VizieR/J/A+AS/129/41
- Title:
- Fe I line shifts in the Sun
- Short Name:
- J/A+AS/129/41
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Central wavelengths measured in the FTS disc-centre spectrum, in the FTS flux spectrum, rest wavelengths, excitation potentials, transition probabilities (log(gfs)) and line equivalent widths at the centre of the disc when available (from Moore et al. 1966 (The Solar Spectrum 2935{AA} to 8770{AA}, National Bureau of Standards Monograph 61) and compiled by A. D. Wittmann, private communication). An asterisk in the equivalent width means that the line has a blend.
