DO R CORONAE BOREALIS STARS FORM FROM DOUBLE WHITE DWARF MERGERS?
Bibliographic record
Abstract
A leading formation scenario for R Coronae Borealis (RCB) stars invokes the merger of degenerate He and CO white dwarfs (WDs) in a binary. The observed ratio of 16 O/ 18 O for RCB stars is in the range of 0.3–20 much smaller than the solar value of ∼500. In this paper, we investigate whether such a low ratio can be obtained in simulations of the merger of a CO and a He WD. We present the results of five three-dimensional hydrodynamic simulations of the merger of a double WD system where the total mass is 0.9 M ☉ and the initial mass ratio ( q ) varies between 0.5 and 0.99. We identify in simulations with q ≲ 0.7 a feature around the merged stars where the temperatures and densities are suitable for forming 18 O. However, more 16 O is being dredged up from the C- and O-rich accretor during the merger than the amount of 18 O that is produced. Therefore, on the dynamical timescale over which our hydrodynamics simulation runs, an 16 O/ 18 O ratio of ∼2000 in the "best" case is found. If the conditions found in the hydrodynamic simulations persist for 10 6 s the oxygen ratio drops to 16 in one case studied, while in a hundred years it drops to ∼4 in another case studied, consistent with the observed values in RCB stars. Therefore, the merger of two WDs remains a strong candidate for the formation of these enigmatic stars.
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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 | 0.001 | 0.002 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.001 | 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".