Observations of the Ultraviolet-bright Star Barnard 29 in the Globular Cluster M13 (NGC 6205)
Bibliographic record
Abstract
Abstract We have analyzed spectra from FUSE, COS, GHRS, and Keck HIRES of the UV-bright star Barnard 29 in M13 (NGC 6205). By comparing the photospheric abundances derived from multiple ionization states of C, N, O, Si, and S, we infer an effective temperature = 21,400 ± 400 K. Balmer-line fits yield a surface gravity = 3.10 ± 0.03. We derive photospheric abundances of He, C, N, O, Mg, Al, Si, P, S, Cl, Ar, Ti, Cr, Fe, Ni, and Ge. Barnard 29 exhibits an abundance pattern typical of the first-generation stars in M13, enhanced in oxygen and depleted in aluminum. An underabundance of C and an overabundance of N suggest that the star experienced nonconvective mixing on the red giant branch (RGB). We see no evidence of significant chemical evolution since the star left the RGB; in particular, it did not undergo third dredge-up. Previous workers found that the star’s far-UV spectra yield an iron abundance about 0.5 dex lower than its optical spectrum, but the iron abundances derived from all of our spectra are consistent with the cluster value. We attribute this difference to our use of model atmospheres without microturbulence, which is ruled out by careful fits to optical absorption features. We derive a mass M */M ⊙ = 0.45–0.55 and luminosity = 3.26–3.35. Comparison with stellar-evolution models suggests that Barnard 29 evolved from a zero-age horizontal branch star of mass M */M ⊙ between 0.50 and 0.55, near the boundary between the extreme and blue horizontal branches.
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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 | 0.000 |
| 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 | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| 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".