Speaker: Stella Stopkowicz, Universität des Saarlandes

The atmospheric composition of white dwarf stars is typically inferred through analysis of their observed spectra, obtained using both Earth-based and space-based telescopes. For example, the Hubble Space Telescope has provided high-resolution ultraviolet spectra critical to such investigations. Accurate interpretation and assignment of these spectra require advanced quantum-chemical calculations to identify the atomic and molecular species present. A significant fraction of white dwarfs exhibit strong magnetic fields, with field strengths reaching up to approximately 100 megagauss (MG), or 100,000 tesla. At lower field strengths, magnetic effects can often be treated as small perturbations. However, this perturbative approach breaks down in the regime of strong magnetic fields, where magnetic interactions lead to complex and non-intuitive alterations of spectral features, greatly complicating their assignment.

In these high-field cases, it becomes necessary to incorporate the magnetic field explicitly within finite-field quantum-chemical frameworks. Such methods allow for the prediction of field-induced shifts, splittings, and changes in transition intensities. This presentation will illustrate examples of these predictive approaches and discuss the specific challenges associated with spectral interpretation under strong magnetic fields. The impact of field-dependent pressure broadening on spectral line profiles will also be addressed.

References

[1] F. Hampe and S. Stopkowicz, J. Chem. Phys. 146, 154105 (2017)
[2] F. Hampe and S. Stopkowicz, J. Chem. Theory Comput. 15, 4036 (2019)
[3] M. A. Hollands, S. Stopkowicz, M.-P. Kitsaras, F. Hampe, S. Blaschke, and J.J. Hermes, Mon. Not. R. Astron. Soc. 520, 3, 3560–3575 (2023)
[4] M.-P. Kitsaras, L. Grazioli, S. Stopkowicz, J. Chem. Phys. 160, 094112 (2024)
[5] S. Blaschke, M.-P. Kitsaras, S. Stopkowicz, Phys. Chem. Chem. Phys. 26, 288 (2024)
[6] M.-P. Kitsaras, F. Hampe, L. Reimund, S. Stopkowicz, https://doi.org/10.48550/arXiv.2505.06976 (2025)