The Rotation of Arcturus and Active Longitudes on Giant Stars
Bibliographic record
Abstract
From two decades of high‐resolution spectroscopic measurements of Arcturus (HR 5340, K2 III), we identify a 2 yr modulation in the velocity span of the bisector of the Fe i λ6252.57 line. It seems likely that this is the rotation period, and we deduce the equatorial rotation rate to be 1.8 ± 0.3 km s −1 , based on a radius of 25.4 R ⊙ . From detailed Fourier analysis of the broadening and shapes of the spectral lines, we derive vsin i = 1.5 ± 0.3 km s −1 and a radial‐tangential macroturbulence dispersion of 5.2 ± 0.2 km s −1 . The inclination of the rotation axis to the line of sight is then 58° ± 25°. Considering the periods found by H.‐J. Choi et al. from variations in the Ca ii H and K line emission, we suggest that giant stars have two or three active longitudes and, therefore, that periods found from the modulation of magnetic features will be one‐half or one‐third of the rotation period.
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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 | 0.000 | 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".