A Magnetic Field Detection in the Massive O-type Bright Giant 63 Oph
Bibliographic record
Abstract
Abstract Surface magnetic fields are detected in less than 10% of the massive O-type star population and even less frequently among “old” massive stars approaching the terminal-age main sequence (TAMS). It is unclear to what extent the rarity of magnetic detections in massive stars near the TAMS is due to magnetic field decay or observational biases. We report the detection of a weak surface magnetic field in the O-type giant 63 Oph (T eff = 35.0 ± 0.3 kK, log g = 3.51 ± 0.03 ) from new ESPaDOnS circularly polarized spectra. The mean longitudinal field strength associated with the magnetic detection is 〈B z 〉 = 84 ± 14 G, which we use to set a lower limit on the dipolar field strength of B p ≥ 300 ± 50 G. We report Balmer line-core equivalent widths (EWs) and radial velocity measurements from the analysis of spectra primarily obtained by the IACOB project with the FEROS, FIES, and HERMES spectrographs. We identify a dominant period of ∼19.8 days in the EWs, which we attribute to the effects of a rotating magnetosphere under the oblique rotator model. We do not identify any coherent signals in a time series analysis of archival Hipparcos, ASAS-SN, and K2 photometry. Our findings show that 63 Oph may be a rare link between strongly magnetic massive stars detected on or near the zero-age main sequence and weakly magnetic O-type supergiants. Additional observations are needed to fully constrain 63 Oph’s magnetic field geometry and magnetospheric properties.
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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 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 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".