The aim of this session is to encourage further dialogue and promote knowledge transfer between astronomers with strong atomic and molecular data needs and those who produce this data from laboratory measurements and calculations. We hope this will foster new collaborations for the future, which, through targeted measurements and calculations, will accelerate the rate at which astronomers’ needs can be met.
Talks and posters will focus on four main areas:
* Data requirements of astronomers
* Laboratory-measured atomic and molecular data
* Theoretical calculations
We encourage all astronomers involved in the ongoing spectroscopic surveys such as Gaia-ESO, APOGEE or GALAH or in future ones such as WEAVE, 4MOST or DESI to attend in order to explain their data needs.
The emphasis throughout the special session will remain on knowledge transfer; with astronomers highlighting their data needs, and spectroscopists and theorists presenting new data of astronomical interest and the capabilities of their facilities for future collaborations.
Juan de Dios, Leticia; Rodríguez, Mónica
Atomic data are an important source of systematic uncertainty in our determinations of nebular chemical abundances. However, we do not have good estimates of these uncertainties since it is very difficult to assess the accuracy of the atomic data involved in the calculations. We explore here the size of these uncertainties by using 52 different sets of transition probabilities and collision strengths, and all their possible combinations, to calculate the physical conditions and the total abundances of O, N, S, Ne, Cl and Ar for a sample of planetary nebulae and H ii regions. We find that atomic data variations introduce differences in the derived abundance ratios as low as 0.1-0.2 dex at low density, but that reach or surpass 0.6-0.8 dex at densities above 104 cm-3 in several abundance ratios, like O/H and N/O. Removing from the 52 data sets the four data sets that introduce the largest differences, the total uncertainties are reduced, but high-density objects still reach uncertainty factors of four for their values of O/H and N/O. We identify the atomic data that introduce most of the uncertainty, which involves the ions used to determine density, namely, the transition probabilities of the S+, O+, Cl++ and Ar+3 density diagnostic lines, and the collision strengths of Ar+3. Improved calculations of these data will be needed in order to derive more reliable values of chemical abundances in high-density nebulae. In the meantime, our results can be used to estimate the uncertainties introduced by atomic data in nebular abundance determinations.
Malmö University and Lund Observatory jointly announce a PhD position in Atomic Astrophysics.
The candidate will work within the project ‘Experimental and Computational Atomic Astrophysics’
For information and online application, please see the link below.
The deadline for application is August 15.
Please forward to potential candidates.
Guzmán, F.; Badnell, N. R.; Chatzikos, M.; van Hoof, P. A. M.; Williams, R. J. R.; Ferland, G. J.
Accurate rates for energy-degenerate l-changing collisions are needed to determine cosmological abundances and recombination. There are now several competing theories for the treatment of this process, and it is not possible to test these experimentally. We show that the H I two-photon continuum produced by astrophysical nebulae is strongly affected by l-changing collisions. We perform an analysis of the different underlying atomic processes and simulate the recombination and two-photon spectrum of a nebula containing H and He. We provide an extended set of effective recombination coefficients and updated l-changing 2s – 2p transition rates using several competing theories. In principle, accurate astronomical observations could determine which theory is correct.
McLaughlin, B. M.; Bizau, J.-M.; Cubaynes, D.; Guilbaud, S.; Douix, S.; Shorman, M. M. Al; Ghazaly, M. O. A. El; Sakho, I.; Gharaibeh, M. F.
Absolute cross-sections for the K-shell photoionization of Be-like (O4 +) and Li-like (O5 +) atomic oxygen ions were measured for the first time (in their respective K-shell regions) by employing the ion-photon merged-beam technique at the SOLEIL synchrotron-radiation facility in Saint-Aubin, France. High-resolution spectroscopy with E/ΔE ≈ 3200 (≈170 meV, full width at half-maximum) was achieved with photon energy from 550 to 670 eV. Rich resonance structure observed in the experimental spectra is analysed using the R-matrix with pseudo-states (RMPS) method. Results are also compared with the screening constant by unit nuclear charge (SCUNC) calculations. We characterize and identify the strong 1s → 2p resonances for both ions and the weaker 1s → np resonances (n ≥ 3) observed in the K-shell spectra of O4 +.
Si, R.; Li, S.; Wang, K.; Guo, X. L.; Chen, Z. B.; Yan, J.; Chen, C. Y.; Brage, T.; Zou, Y. M.
Aims: Spectral lines of He-like ions are among the most prominent features in X-ray spectra from a large variety of astrophysical and high-temperature fusion plasmas. A reliable plasma modeling and interpretation of the spectra require a large amount of accurate atomic data related to various physical processes. In this paper, we focus on the electron-impact excitation (EIE) process.
Methods: We adopted the independent process and isolated resonances approximation using distorted waves (IPIRDW). Resonant stabilizing transitions and decays to lower-lying autoionizing levels from the resonances are included as radiative damping. To verify the applicability of the IPIRDW approximation, an independent Dirac R-matrix calculation was also performed. The two sets of results show excellent agreement.
Results: We report electron impact excitation collision strengths for transitions among the lowest 49 levels of the 1snl(n ≤ 5,l ≤ (n-1)) configurations in He-like ions with 20 ≤ Z ≤ 42. The line ratios R and G are calculated for Fe XXV and Kr XXXV.
Conclusions: Compared to previous theoretical calculations, our IPIRDW calculation treats resonance excitation and radiative damping effects more comprehensively, and the resulting line emission cross sections show good agreement with the experimental observations. Our results should facilitate the modeling and diagnostics of various astrophysical and laboratory plasmas.