Bibliographic record
Abstract
Stellar evolution models of a 0.8 M ☉ star ( Y = 0.2352, Z = 0.0001, α = 0.3) have been calculated in detail from the zero-age main sequence to the horizontal branch, both with and without atomic diffusion. We analyze the effects of atomic diffusion on the horizontal branch models themselves, as well as on the properties of giant-branch tip stars that determine the location of horizontal branch stars on the H-R diagram. It leads to a He core mass increase of 0.0025 M ☉ . There are also concentration differences of up to ~0.04 dex for most metals between the He core and the exterior to the core. It is generally assumed in evolution calculations of horizontal branch stars that overshooting plays an important role in ensuring convective neutrality at the helium-burning core boundary, causing a 50% increase in the mass of the convective core. It is shown here that atomic diffusion can play this role, although a contribution from overshooting is not excluded. Atomic diffusion is also shown to lead to some hydrogen burning within the He core. Some hydrogen diffuses toward the center and leads to a CN cycle involving C produced at the time of the He flash. This increases the zero-age horizontal branch luminosity. The sensitivity to thorough mixing of the He core is discussed. The cumulative effect is to lead to a luminosity difference of 0.015 ± 0.005 dex in zero-age horizontal branch stars between models with and without diffusion. This will have a small effect on the ages of globular clusters if their distances are based on the predicted luminosities of HB 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 | 0.000 | 0.003 |
| 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 | 0.000 |
| Scholarly communication | 0.002 | 0.002 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.016 | 0.001 |
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".