δ Ceti Is Not Monoperiodic: Seismic Modeling of a β Cephei Star from<i>MOST</i>Space‐based Photometry
Bibliographic record
Abstract
The β Cephei star δ Ceti was considered one of the few monoperiodic variables in its class. Despite (or perhaps because of) its apparently simple oscillation spectrum, it has been challenging and controversial to identify this star's pulsation mode and constrain its physical parameters seismically. Broadband time-resolved photometry of δ Ceti spanning 18.7 days with a duty cycle of about 65% obtained by the Microvariability and Oscillations of Stars ( MOST ) satellite—the first scientific observations ever obtained by MOST —reveals that the star is actually multiperiodic. Besides the well-known dominant frequency of f 1 = 6.205886 day -1 , we have discovered in the MOST data its first harmonic 2 f 1 and three other frequencies ( f 2 = 3.737, f 3 = 3.673, and f 4 = 0.318 day -1 ), all detected with a signal-to-noise ratio > 4. In retrospect, f 2 was also present in archival spectral line-profile data but at lower S/N. We present seismic models whose modes match exactly the frequencies f 1 and f 2 . Only one model falls within the common part of the error boxes of the star's observed surface gravity and effective temperature from photometry and spectroscopy. In this model, f 1 is the radial ( l = 0) first overtone, and f 2 is the g 2 ( l = 2, m = 0) mode. This model has a mass of 10.2 ± 0.2 M ☉ and an age of 17.9 ± 0.3 Myr, making δ Ceti an evolved β Cephei star. If f 2 and f 3 are rotationally split components of the same g 2 mode, then the star's equatorial rotation velocity is either 27.6 km s -1 or half this value. Given its v sin i of about 1 km s -1 , this implies that we are seeing δ Ceti nearly pole-on.
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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 | 0.000 |
| 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 | 0.001 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.003 | 0.001 |
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".