THE CARINA PROJECT. VII. TOWARD THE BREAKING OF THE AGE-METALLICITY DEGENERACY OF RED GIANT BRANCH STARS USING THE<i>C</i><sub>U, B, I</sub>INDEX
Bibliographic record
Abstract
We present an analysis of photometric and spectroscopic data of the Carina dSph galaxy, testing a new approach similar to that used to disentangle multiple populations in Galactic globular clusters (GCs). We show that a proper color combination is able to separate a significant fraction of the red giant branch (RGB) of the two main Carina populations (the old one, ∼12 Gyr, and the intermediate-age one, 4–8 Gyr). In particular, the c U, B, I = ( U − B ) − ( B − I ) pseudo-color allows us to follow the RGB of both populations along a relevant portion of the RGB. We find that the oldest stars have a more negative c U, B, I pseudo-color than intermediate-age ones. We correlate the pseudo-color of RGB stars with their chemical properties, finding a significant trend between the iron content and the c U, B, I . Stars belonging to the old population are systematically more metal-poor ([Fe/H] =−2.32 ± 0.08 dex) than the intermediate-age ones ([Fe/H] =−1.82 ± 0.03 dex). This gives solid evidence of the chemical evolution history of this galaxy, and we have a new diagnostic that can allow us to break the age–metallicity degeneracy of H-burning advanced evolutionary phases. We compared the distribution of stars in the c U, B, I plane with theoretical isochrones, finding that no satisfactory agreement can be reached with models developed in a theoretical framework based on standard heavy element distributions. Finally, we discuss possible systematic differences when compared with multiple populations in GCs.
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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 | 0.002 | 0.003 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.002 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.003 | 0.001 |
| Open science | 0.001 | 0.002 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.006 | 0.006 |
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".