On the Possible Role of Carbon Chains as Carriers of Diffuse Interstellar Bands
Bibliographic record
Abstract
Because the laboratory gas-phase electronic spectra of only the three polyatomic bare carbon chains C 3 , C 4 and C 5 are available, we have made a further attempt to detect the origin bands of C 4 (3789 Å) and C 5 (5109 Å) in the diffuse cloud toward ζ Oph. The measurements provide an improved 3 σ limit to their column densities: N (C 4 ) ≤ 5 × 10 11 cm -2 and N (C 5 ) ≤ 1 × 10 11 cm -2 , with a signal-to-noise ratio (S/N) of 42,000 and 31,000 Å -1 , respectively, at a resolution of 110,000. The limits to N (C 4 ) and N (C 5 ) are lower than predictions from the chemical model used by Roueff and coworkers for such diffuse clouds. In conjunction with observations of related, hydrogen-containing polar chains in the millimeter region and laboratory studies of the electronic transitions of a number of homologous series, these results lead to interesting conclusions about the role of carbon chains as potential carriers of the diffuse interstellar bands (DIBs). First, the abundance and oscillator strength of smaller chains, say up to 10 atoms, are too small to account for the stronger DIBs. Second, because of the electronic configurations of these open-shell species, the lowest energy π-π transition does not have a large oscillator strength but the higher energy one in the UV does, and the chains would have to be prohibitively long for these absorptions to shift into the DIB 4000-9000 Å wavelength region. The exceptions are closed-shell systems such as the odd-numbered bare carbon chains, and the ones in the C 15 -C 31 size range that have their very strong transitions in this region. These species should be a major goal for laboratory and subsequent astronomical studies.
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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 | 0.003 |
| 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 | 0.003 | 0.001 |
| Insufficient payload (model declined to judge) | 0.036 | 0.006 |
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".