Magnetic Field Evolution for Crystallization-driven Dynamos in C/O White Dwarfs
Bibliographic record
Abstract
Abstract We investigate the evolution of magnetic fields generated by the crystallization-driven dynamo in carbon–oxygen white dwarfs (WDs) with masses ≲1.05 M ⊙ . We use scalings for the dynamo to demonstrate that the initial magnetic field strength ( B 0 ) has an upper limit that depends on the initial convection zone size ( R out,0 ) and the WD mass. We solve the induction equation to follow the magnetic field evolution after the dynamo phase ends. We show that the predicted surface magnetic field strength ( B surf ) differs from B 0 by at least a factor of ∼0.3. This reduction depends on R out,0 , where values smaller than half of the star radius give B surf ≲ 0.01 B 0 . We implement electrical conductivities that account for the solid phase effect on the ohmic diffusion. We observe that the conductivity increases as the solid core grows, freezing in the magnetic field at a certain point of the evolution and slowing its outward transport. We study the effect of turbulent magnetic diffusivity induced by the convection and find that for a small R out,0 , B surf is stronger than the nonturbulent diffusion cases because of the more rapid transport, but still orders of magnitude smaller than B 0 . Given these limitations, the crystallization-driven dynamo theory could explain only magnetic C/O WDs with field strengths less than a few megagauss for the mass range 0.45–1.05 M ⊙ . Our results also suggest that a buried fossil field must be at least 100 times stronger than observed surface fields if crystallization-driven convection is responsible for its transport to the surface.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".