The origin of the magnetic fields in white dwarfs (WDs) remains mysterious. Magnetic WDs are traditionally associated with field strengths ≳1 MG, set by the sensitivity of typical spectroscopic magnetic field measurements. Informed by recent developments in red giant magnetoasteroseismology, we revisit the use of WD pulsations as a seismic magnetometer. WD pulsations primarily probe near-surface magnetic fields, whose effect on oscillation mode frequencies is to asymmetrize rotational multiplets and, if strong enough, suppress gravity-mode propagation altogether. The sensitivity of seismology to magnetic fields increases strongly with mode period and decreases quickly with the depth of the partial ionization-driven surface convective zone. We place upper limits for the magnetic fields in 24 pulsating WDs: 20 hydrogen-atmosphere (DAV) and three helium-atmosphere (DBV) carbon–oxygen WDs, and one extremely low-mass (helium-core) pulsator. These bounds are typically ∼1–10 kG, although they can reach down to ∼10–100 G for DAVs and helium-core WDs in which lower-frequency modes are excited. Seismic magnetometry may enable new insights into the formation and evolution of WD magnetism.
Supersensitive Seismic Magnetometry of White Dwarfs
Abstract
Copyright and License
© 2025. The Author(s). Published by the American Astronomical Society.
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Acknowledgement
We thank Sivan Ginzburg for helpful discussions and comments on the manuscript, as well as the anonymous referee for useful suggestions. We are grateful for support from the United States–Israel Binational Science Foundation through grant BSF-2022175. N.Z.R. acknowledges support from the National Science Foundation Graduate Research Fellowship under grant No. DGE-1745301.
Software References
MESA (B. Paxton et al. 2011, 2013, 2015, 2018), NumPy (T. E. Oliphant et al. 2006), SciPy (P. Virtanen et al. 2020), AstroPy (T. P. Robitaille et al. 2013), Matplotlib (J. D. Hunter 2007; T. M. D. Team 2024)
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Additional details
- Alternative title
- Supersensitive seismic magnetometry on white dwarfs
- United States-Israel Binational Science Foundation
- BSF-2022175
- National Science Foundation
- DGE-1745301
- Accepted
-
2025-01-27Accepted
- Available
-
2025-02-27Published
- Caltech groups
- Astronomy Department, TAPIR
- Publication Status
- Published