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Improved algorithms for calculating low temperature dielectronic recombination rate coefficients in photoionized astrophysical plasmas

Presentation #124.09 in the session Laboratory Astrophysics Division (LAD): iPosters.

Published onJul 01, 2023
Improved algorithms for calculating low temperature dielectronic recombination rate coefficients in photoionized astrophysical plasmas

Dielectronic recombination (DR) is one of the most important mechanisms for electron recombination in astrophysical plasmas, requiring both accurate atomic structures and transition rates. In this work, we address the issue of low temperature DR rate coefficients for astrophysical photoionized plasmas, where the DR rates are known to have large uncertainties in their calculated values. This is done through large configuration-interaction (CI) calculation using the AUTOSTRUCTURE code.

Although effective in the high temperature case, current theoretical methods are known to have large uncertainties in the low temperature regime due to uncertainties in calculating low-n doubly excited states. This can be seen from discepancies with storage ring measurements. A commonly used code for computing DR rates is AUTOSTRUCTURE, which uses the multi-configuration Breit-Pauli approach. We have developed an algorithmic method for the generation of large configuration sets to improve the low temperature DR modeling through CI, comparing with existing storage ring measurements. This work is in collaboration with new measurements being performed at the heavy ion storage ring CRYRING@ESR at the FAIR facility in Darmstadt, Germany.

We also consider the commonly used method for calculating Auger rates: Fermi’s golden rule. Although Fermi’s golden rule has been the standard approach, it can be shown that the integral used in Fermi’s golden rule is equivalent to the first order term of the Dyson series, a more complete picture of quantum transitions. We outline a method that can be used in future calculations to quantify the uncertainty of Fermi’s golden rule for Auger rates by determining the rate of convergence of the Dyson series.

In summary, we are developing methods to more accurately calculate resonance positions and heights for low temperature DR rate coefficients.

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