The spin rates of O stars in WR + O binaries – I. Motivation, methodology, and first results from SALT
Bibliographic record
Abstract
The black holes (BH) in merging BH–BH binaries are likely progeny of binary O stars. Their properties, including their spins, will be strongly influenced by the evolution of their progenitor O stars. The remarkable observation that many single O stars spin very rapidly can be explained if they accreted angular momentum from a mass-transferring, O-type or Wolf–Rayet (WR) companion before that star blew up as a supernova. To test this prediction, we have measured the spin rates of eight O stars in WR + O binaries, increasing the total sample size of such O stars’ measured spins from 2 to 10. Polarimetric and other determinations of these systems’ sin i allow us to determine an average equatorial rotation velocity from He i (He ii) lines of ve = 348 (173) km s−1 for these O stars, with individual star's ve from He i (He ii) lines ranging from 482 (237) to 290 (91) km s−1. We argue that the ∼100 per cent difference between He i and He ii speeds is due to gravity darkening. Supersynchronous spins, now observed in all 10 O stars in WR + O binaries where it has been measured, are strong observational evidence that Roche lobe overflow mass transfer from a WR progenitor companion has played a critical role in the evolution of WR + OB binaries. While theory predicts that this mass transfer rapidly spins up the O-type mass gainer to a nearly breakup rotational velocity of ve ∼ 530 km s−1, the observed average ve of the O-type stars in our sample is 65 per cent of that speed. This demonstrates that, even over the relatively short WR-phase time-scale, tidal and/or other effects causing rotational spin-down must be efficient. A challenge to tidal synchronization theory is that the two longest period binaries in our sample (with periods of 29.7 and 78.5 d) unexpectedly display supersynchronous rotation.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| 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".