Multiline study of the radial extent of SiO, CS, and SiS in asymptotic giant branch envelopes
Bibliographic record
Abstract
Circumstellar envelopes around asymptotic giant branch (AGB) stars contain a rich diversity of molecules, whose spatial distribution is regulated by different chemical and physical processes. In the outer circumstellar layers, all molecules are efficiently destroyed due to interactions with interstellar ultraviolet photons. Here we aim to carry out a coherent and uniform characterization of the radial extent of three molecules (SiO, CS, and SiS) in envelopes around O- and C-rich AGB stars, and to study their dependence on mass-loss rate. To this end, we observed a reduced sample of seven M-type and seven C-type AGB envelopes in multiple lines of SiO, CS, and SiS with the Yebes 40 m and IRAM 30 m telescopes. The selected sources cover a wide range of mass-loss rates, from ~10 −7 M ⊙ yr −1 to a few times 10 −5 M ⊙ yr −1 , and the observed lines cover a wide range of upper-level energies, from 2 K to 130 K. We carried out excitation and radiative transfer calculations over a wide parameter space in order to characterize the abundance and radial extent of each molecule. A χ 2 analysis indicates that the abundance is usually well constrained while the radial extent is in some cases more difficult to constrain. Our results indicate that the radial extent of the molecules considered here increases with increasing envelope density, in agreement with previous observational findings. At high envelope densities of Ṁ / υ ∞ > 10 −6 M ⊙ yr −1 km −1 s, SiO, CS, and SiS show a similar radial extent, while at low envelope densities of Ṁ / υ ∞ < 10 −7 M ⊙ yr −1 km −1 s, differences in radial extent appear among the three molecules, in agreement with theoretical expectations based on destruction due to photodissociation. At low envelope densities, we find a sequence of increasing radial extent, SiS → CS → SiO. We also find a tentative dependence of the radial extent on the chemical type (O- or C-rich) of the star for SiO and CS. Interferometric observations and further investigation of the photodissociation of SiO, CS, and SiS should provide clarification of the situation in regards to the relative photodissociation radii of SiO, CS, and SiS in AGB envelopes and their dependence on envelope density and C/O ratio.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| 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 | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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 teacher head, 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".