The Globular Cluster ω Centauri and the Oosterhoff Dichotomy
Bibliographic record
Abstract
CCD observations obtained by the OGLE team for 128 RR Lyrae variables in ω Centauri have been analyzed. The period-luminosity and period-amplitude plots indicate that, in addition to fundamental (RRab) and first overtone (RRc) pulsators, the ω Centauri RR Lyrae population seems to include second overtone (RRe) and possibly third-overtone pulsators. The mean period for the 59 RRab stars is 0 649, for the 48 RRc stars, it is 0 383, and for the 21 RRe stars, it is 0 304. The mean periods derived for the RRab and RRc stars are typical values for an Oosterhoff type II (OoII) cluster. Nevertheless, the period-amplitude plot also shows that some of the RR Lyrae variables have "Oosterhoff type I" (OoI) characteristics. Most of the second-overtone variables exhibit nonradial pulsations similar to those recently detected in some of the RR Lyrae variables in the clusters M55 and M5, in the Galactic bulge, and in the LMC. Relative luminosities derived for the RRc variables from Fourier coefficients correlate with the observed apparent magnitudes. Masses for the RRc stars have been calculated from Fourier coefficients. A comparison of the derived masses for RRc stars in the four OoII clusters ω Cen, M15, M55, and M68 indicates that the masses of the RRc stars in M15 and M68 are almost 0.2 M ⊙ greater than those in the other two. Since M15 and M68 have a high frequency of RRd stars among their first-overtone pulsators, while none have been identified in ω Cen or M55, this suggests that the double-mode pulsation phenomenon may be associated with mass. Among the RRc variables in ω Cen, the OoII variables have lower derived masses and higher luminosities than the OoI variables. An application of the period-density law to pairs of OoI and OoII RRab stars selected according to their position in the period-amplitude plot also indicates that the OoII variables in general have lower masses and higher luminosities. These findings support the hypothesis that the RR Lyrae variables in OoII systems are evolved horizontal-branch stars that spend their zero-age horizontal-branch phase on the blue side of the instability strip.
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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 | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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".