A Chemical Model of the Neutral Envelope of the Planetary Nebula NGC 7027
Bibliographic record
Abstract
In response to the recent molecular observations by ISO and millimeter-wave telescopes, we have developed a spherically symmetric, steady state chemical model for the planetary nebula NGC 7027. In our model, the neutral envelope consists of a geometrically thin, high-density shell of constant density and an outer stellar wind region with an inverse-square law density profile. The neutral envelope is subjected to ultraviolet (UV) radiation both from the central star and from the external interstellar field. Under an assumed visual extinction of 4 mag for the neutral envelope, the gas in our model is half molecular and half atomic. Simple molecules such as CH, CH + , OH are abundantly formed at an assumed gas temperature of 800 K in the partially molecular shell. The presence of molecular ions such as HCO + and CO + is well explained by photochemistry at high temperatures. The model CN/HCN ratio is almost constant at about 30 throughout the wind region and is 1-10 in the dense shell, comparable to observed values in planetary nebulae. Our model suggests that molecules are as efficiently formed with timescales shorter than 100 yr as they are photodissociated in the neutral envelope of NGC 7027 and probably in other young planetary nebulae.
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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 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".