Do All Low-Mass Stars Undergo Extra Mixing Processes?
Bibliographic record
Abstract
Abstract Standard stellar evolution models that only consider convection as a physical process to mix material inside of stars predict the production of significant amounts of 3 He in low-mass stars ( M < 2 M ⊙ ), with peak abundances of 3 He/H ∼ few × 10 −3 by number. Over the lifetime of the Galaxy, this ought to produce 3 He/H abundances that diminish with increasing Galactocentric radius. Observations of 3 He + in H ii regions throughout the Galactic disk, however, reveal very little variation in the 3 He abundance with values of 3 He/H similar to the primordial abundance, 3 H e / H p ∼ 10 − 5 . This discrepancy, known as the “ 3 He problem,” can be resolved by invoking in stellar evolution models an extra mixing mechanism due to the thermohaline instability. Here we observe 3 He + in the planetary nebula (PN) J320 (G190.3–17.7) with the Jansky Very Large Array to confirm a previous 3 He + detection made with the Very Large Array that supports standard stellar yields. This measurement alone indicates that not all stars undergo extra mixing. Our more sensitive observations do not detect 3 He + emission from J320 with an rms noise of 58.8 μ Jy beam −1 after smoothing the data to a velocity resolution of 11.4 km s −1 . We estimate an abundance limit of 3 He/H ≤ 2.75 × 10 −3 by number using the numerical radiative transfer code NEBULA. This result nullifies the last significant detection of 3 He + in a PN and allows for the possibility that all stars undergo extra mixing processes.
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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 | 0.001 | 0.004 |
| 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 | 0.002 | 0.002 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.010 | 0.002 |
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".