A Distance-Independent Age for the Globular Cluster M92
Bibliographic record
Abstract
We use deep Strömgren CCD photometry to determine the age of the globular cluster M92 (NGC 6341) from the [( v - y ) 0 , c 0 ]-diagram. Besides being completely independent of distance, this color-color plot has the further advantage that it is not very sensitive to the amount of foreground interstellar absorption. The main disadvantage of this approach is that it relies heavily on the accuracy of the T eff and color scales of isochrones. As these aspects of the models continue to be uncertain, absolute ages cannot be derived in this way to within a few gigayears. For instance, while we obtain an age of 14.5 Gyr for M92 using the latest University of Victoria isochrones, an age as low as 12 Gyr or as high as 17 Gyr would be found if we adopted different zero points for the synthetic color– T eff relations or an ad hoc shift of ≈±200 K were applied to the models. However, much tighter constraints on the age may be obtained by invoking some additional constraints. To be specific, we find from the ( v - y , c 1 )-diagram that the extremely metal-deficient field halo stars are most likely coeval with M92 to within 1 Gyr (1 σ error bar) and that the properties of the well-observed [Fe/H] ≈ -2.5 subgiant HD 140283, which has σ π /π = 0.06 from Hipparcos , imply ( m - M ) V ≲ 14.60 and an age ≳16 Gyr for M92. This, in fact, offers considerable support for the synthetic colors that we have used.
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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 | 0.002 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 0.002 |
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".