The Pleiades, Coma, Hyades, and Praesepe open clusters: Li, Al, Si, S, Fe, Ni, and Eu abundances compared in A stars ?
Bibliographic record
Abstract
In the third of a series of papers on the A stars in open clusters, the Coma and Hyades clusters are revisited; in the first and second papers, the Pleiades and Praesepe were respectively investigated. All the spectra were secured with the Canada-France-Hawaii telescope at high spectral resolution and high signal-to-noise ratios. Photospheric abundances have been determined for Li, Al, Si, S, Fe, Ni, and Eu from model atmo- sphere abundance analysis. All the A stars with enough-sharp lines to be studied for Li were observed in the four clusters. Abundance results are summarized for 31 cluster members, in- cluding 21 Am, 7 normal A, and 3 early-A stars. The Am stars have very uniform Li, Al, Si, S, and Fe abun- dances in a large temperature range of nearly 1000 K. Compared to normal A stars, Li is significantly deficient in Am stars (by a factor of 3), Al marginally overabundant, Si, S, and Fe are the same, Ni and Eu (with only a few results) overabundant. Those uniform abundances of Li, Al, Si, S, or Fe in Am stars involve that abundances are little affected by the magnitude of the rotational velocity. For both Am and normal A samples, no abundance trend as a function of age and/or evolution is detected in the case of Li, Al, Si, S, or Fe. The ages considered are in the range 0. 8-71 0 8 years; the evolution is limited from the ZAMS to the cluster turn-off. The build-up of the chemical abundances studied, in particular the Li differentiation between Am and normal A stars, could have taken place very early when the stars arrive on the Main Sequence. The spread in lithium found for the A stars is reminiscent of that reported in the field and one open cluster for stars of nearly the same mass and slightly evolved out of the Main Sequence. The Li abundance does not change as soon as the star evolves through the subgiant phase and the convection zone becomes deeper. There are two exceptional Am stars: one, in the Hyades, is Li-deficient and the other, in Praesepe, Li-overabundant. They are no obvious circumstances that can distinguish both stars from others in the very same region of their respective cluster sequence. In each of the four clusters, the maximum Li abun- dance is found in A stars, generally in normal A stars.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 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) | 0.000 | 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 teacher head, 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".