Metallicity effects on classical Cepheids: Velocity curve morphology of outer disc Cepheids
Bibliographic record
Abstract
We present new radial velocity data for eleven classical Cepheids situated in the outer parts of the Galactic disc. The resultant velocity curves for these metal-deficient Cepheids are decomposed in Fourier parameters, and compared to solar-metallicity Cepheid data, in order to study the effect of metallicity on the pulsation properties. Up to 8 days, the phase shift is found to follow very closely the corresponding sequence for solar-metallicity Cepheids, indicating the absence of metallicity effects on for low periods. However, metal-deficient Cepheids show a slightly larger A1 amplitude and R21 amplitude ratio for days. At days, there is some evidence that the phase shift is significantly larger for metal-deficient Cepheids than at solar metallicity. A posteriori, this effect is also detected in photometric data for outer disc and LMC Cepheids in the 12-20 day period range. In good qualitative agreement with the predictions of theoretical pulsation models, we therefore see some indication of a metallicity dependence of the resonance properties. The largest effects on velocity curve shape are expected in the crucial 8-12 day period range -around the resonance for fundamental-mode Cepheids -that is not covered by our data. Possible targets for future measurements are suggested to fill this gap, and to improve the quantitative determination of metallicity effects on the structural properties of Cepheid velocity curves.
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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 | 0.000 | 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".