- ID:
- ivo://CDS.VizieR/J/A+A/420/763
- Title:
- Electron impact excitation of NiII
- Short Name:
- J/A+A/420/763
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the effects of using a 4d{bar} pseudo-orbital on the collision strengths for electron impact excitations of forbidden transitions in Ni II computed in the close coupling approximation. It is found that the resonance structures of the collision strengths are quite sensitive to the way the pseudo-orbital is created. Further, the close coupling expansion with a single 4d{bar} orbital does not converge, resulting in a poor representation of (N+1)-electrons auto-ionizing states. Much greater expansions are needed to properly represent resonance structures in electron impact excitation calculations, resulting in variations of up to factors of two, with respect to previous computations, in the Maxwellian averaged excitation rate coefficients.
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- ID:
- ivo://CDS.VizieR/J/MNRAS/436/1452
- Title:
- Electron impact for OV and OVI levels
- Short Name:
- J/MNRAS/436/1452
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Radiative atomic and electron impact excitation data for OV and OVI ions have been calculated. The radiative atomic data have been calculated with the AUTOSTRUCTURE code. Besides the one-body and the two-body fine structure interactions, the two-body non-fine structure operators of the Breit-Pauli Hamiltonian, namely contact spin-spin, two-body Darwin and orbit-orbit are incorporated in AUTOSTRUCTURE. The scattering problem has been treated in the Breit-Pauli distorted wave approximation using the same code AUTOSTRUCTURE. The OV atomic calculations have been extended from 46 to 92 levels. We have calculated excitation cross sections for the OV 2s^2^-2s2p and the OVI 2s-2p transitions at energies near the corresponding excitation threshold regions. We have also calculated collision strengths for transitions from the most important levels for collisional excitation at electron energies up to 120Ry for OV and up to 140Ry for OVI. Our results have been compared with the available theoretical/experimental ones and a satisfactory agreement have been found between them.
- ID:
- ivo://CDS.VizieR/J/A+A/626/A123
- Title:
- Electron impact ionisation data
- Short Name:
- J/A+A/626/A123
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The aim of this work is to improve the modelling of ion populations in higher density, lower temperature astrophysical plasmas, of the type commonly found in lower solar and stellar atmospheres. Ion population models for these regions frequently employ the coronal approximation, which assumes conditions more suitable to the upper solar atmosphere, where high temperatures and lower densities prevail. The assumed conditions include all ions being in the ground state and steady-state equilibrium, where there is sufficient time for ionisation and recombination to take place. Using the coronal approximation for modelling the solar transition region gives theoretical lines intensities for the Li-like and Na-like isoelectronic sequences which are often factors of two to five times lower than observed. The works of Burgess & Summers (1969ApJ...157.1007B) and Nussbaumer & Storey (1975A&A....44..321N) show the important part ions in excited levels play when included in the modelling. As density increases metastable levels become populated and ionisation rates increase, whereas dielectronic recombination through highly excited levels is suppressed. Photo-ionisation is also shown by Nussbaumer & Storey to have an effect on the charge-state distribution of carbon in these regions. Their models, however, use approximations for the atomic rates to determine the ion balance. Presented here is the first stage in rates to determine the ion balance. Presented here is the first stage in updating these earlier models of carbon by using rates from up-to-date atomic calculations and more recent photo-ionising radiances. Where atomic rates were not readily available, in the case of electron impact direct ionisation and excitation-auto-ionisation, new calculations were made using the Flexible Atomic Code and Autostructure, and compared to theoretical and experimental studies. The effects each atomic process has on the ion populations as density changes is illustrated, and final results from the modelling are compared to the earlier works. Lastly, the new results for ion populations were used to predict line intensities for the solar transition region in the quiet Sun. In comparison to coronal approximation modelling the new results show significantly improved agreement with observations.
- ID:
- ivo://CDS.VizieR/J/ApJ/850/122
- Title:
- Electron-impact multiple-ionization cross sections
- Short Name:
- J/ApJ/850/122
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We compiled a set of electron-impact multiple-ionization (EIMI) cross section for astrophysically relevant ions. EIMIs can have a significant effect on the ionization balance of non-equilibrium plasmas. For example, it can be important if there is a rapid change in the electron temperature or if there is a non-thermal electron energy distribution, such as a kappa distribution. Cross section for EIMI are needed in order to account for these processes in plasma modeling and for spectroscopic interpretation. Here, we describe our comparison of proposed semiempirical formulae to available experimental EIMI cross-section data. Based on this comparison, we interpolated and extrapolated fitting parameters to systems that have not yet been measured. A tabulation of the fit parameters is provided for 3466 EIMI cross sections and the associated Maxwellian plasma rate coefficients. We also highlight some outstanding issues that remain to be resolved.
- ID:
- ivo://CDS.VizieR/J/AJ/135/1580
- Title:
- Element abundances in ten red giants of Car dSph
- Short Name:
- J/AJ/135/1580
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have obtained high-resolution spectroscopy of ten red giants in the Carina dwarf spheroidal (dSph) galaxy with the ultraviolet and visual echelle spectrograph at the European Southern Observatory Very Large Telescope in order to study the detailed chemical evolution of this Galactic satellite. Here we present the abundances of O, Na, Mg, Si, Ca, Ti, and Fe.
- ID:
- ivo://CDS.VizieR/J/A+A/465/185
- Title:
- Element abundances of 7 stars of NGC 6253
- Short Name:
- J/A+A/465/185
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have carried out a big FLAMES survey of 10 Galactic open clusters aiming at different goals. One of them is the determination of chemical abundances, in order to put constraints on the radial metallicity gradient in the disk and its evolution. One of the sample clusters is the very metal rich NGC 6253. We have obtained UVES high resolution spectra of seven candidate clusters members (from the turn off up to the red clump) with the goal of determining the chemical composition of NGC 6253 and to investigate its origin and role in the interpretation of the radial metallicity gradient in the disk.
- ID:
- ivo://CDS.VizieR/J/A+A/354/899
- Title:
- Elemental abundance analyses IV.
- Short Name:
- J/A+A/354/899
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using new CASLEO echelle spectrograms, we extended our elemental abundances of the sharp-lines Mercury-Manganese star {mu} Lep, 14 Hya, {kappa} Cnc, HR 4487, 28 Her, and HR 7245, the closely related star 3 CenA, and 7 Sex an A0V star with population I abundances, but with Population II star space motion. The {lambda}{lambda}4500-6200 region contains a sufficient number of lines to derive high-quality abundances of these stars. For most stars, the new spectra provide additional lines for the analyses which improve their quality as well as help fill in the periodic table.
- ID:
- ivo://CDS.VizieR/J/AN/329/4
- Title:
- Elemental abundance analyses of nu Her & 41 Cyg
- Short Name:
- J/AN/329/4
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This series of high quality elemental abundance analyses of mostly Main Sequence normal and peculiar B, A, and F stars defines their properties and provides data for the comparison with analyses of somewhat similar stars and with theoretical predictions. Most use high dispersion and high S/N (greater than or equal to 200) spectrograms obtained with CCD detectors at the long camera of the 1.22-m Dominion Astrophysical Observatory telescope's coude spectrograph. Here we expand the range of stars examined to include two relatively quiescent F supergiants. nu Her (F2 II) and 41 Cyg (F5 Ib-II) are analyzed as consistently as possible with previous studies. These LTE fine analyses use the ATLAS9 and the WIDTH9 programs of R.L. Kurucz. High signal-to-noise spectrograms and high quality atomic data were employed. The derived values of these photometrically constant stars are somewhat different with the abundances of nu Her being somewhat metal-poor and those of 41 Cyg being crudely solar-like. Our analyses indicate that the basic results of Luck and Wepfer who also studied nu Her and 41 Cyg are not likely to be significantly changed by new studies of all their stars.
- ID:
- ivo://CDS.VizieR/J/A+A/447/685
- Title:
- Elemental abundance analyses. XXIX.
- Short Name:
- J/A+A/447/685
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We performed elemental abundances analyses of the mercury-manganese (HgMn) stars 53 Tau, {beta} Tau, and {gamma} Crv consistent with previous studies of similar stars in this series.
- ID:
- ivo://CDS.VizieR/J/MNRAS/356/1256
- Title:
- Elemental abundance analysis of HR 8216
- Short Name:
- J/MNRAS/356/1256
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have performed the abundance analysis of the cool magnetic CP star HR 8216 (=HD 204411) using 2.4{AA}/mm Dominion Astrophysical Observatory Reticon exposures covering ll 3830-4770{AA} with a typical signal-to-noise ratio of 200. The spectrograms were measured interactively with the graphics computer program REDUCE. We performed a fine analysis with an ATLAS9 metal-rich model atmosphere whose predictions best matched the optical region fluxes and the Hg profile. HR 8216's anomalies are primarily an enhancement of many iron peak elements with the rare earths elements much less enhanced than for many similar cool magnetic CP stars .Using the results of the fine analysis we synthetized the spectrum. Comparison with the observed spectrum showed that agreement is better.