On the Old Open Clusters M67 and NGC 188: Convective Core Overshooting, Color‐Temperature Relations, Distances, and Ages
Bibliographic record
Abstract
The color‐magnitude diagram of M67 is used to constrain the value of the parameter F over in its ≈1.3 M ⊙ turnoff stars: F over is effectively the fraction of the maximum possible extent of convective core overshooting predicted by the Roxburgh (1989, A&A, 211, 361) criterion. Isochrones that treat overshooting using the parameterized Roxburgh criterion are able to reproduce the morphology of the cluster turnoff, including the luminosity of the gap, if F over ≈ 0.07 (assuming current best estimates for the reddening and metallicity). Previous studies have derived values of F over near 0.5 in open clusters of similar metallicity but having turnoff masses ≥1.55 M ⊙ , indicating that the overshooting parameter is a strong function of mass in the lowest mass stars that retain convective cores throughout the main‐sequence phase. NGC 188 appears to be too old for core overshooting to play any role in the evolution of stars that are currently in the core H‐burning phase, but the availability of well‐calibrated BVRI photometry for this system, together with Landolt photometric standards, provides valuable tests of the color‐T eff relations that apply to [Fe/H] ≈ 0.0 stars. Our analysis of color‐color diagrams, in particular, suggests that the Castelli ( 1999 , A&A, 346, 564) V−R and V−I transformations for lower gravity stars are more realistic than those published recently by VandenBerg & Clem (2003, AJ, 126, 778). The same color‐color diagrams also indicate that the differences in recent (V−I,V) diagrams for M67 appear to be due, at least in part, to the difficulty of defining the standard VRI photometric system. The ages of M67 and NGC 188 that have been derived in this study are 4.0 and 6.8 Gyr, respectively, which is consistent with other modern determinations.
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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 | 0.002 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.002 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".