Water Absorption from Line‐of‐Sight Clouds toward W49A
Bibliographic record
Abstract
We have observed six clouds along the line of sight toward W49A using the Submillimeter Wave Astronomy Satellite and several ground-based observatories. The ortho-H 2 O 1 10 → 1 01 and OH (1665 and 1667 MHz) transitions are observed in absorption , whereas the low- J CO, 13 CO, and C 18 O lines, as well as the [C I] 3 P 1 - 3 P 0 transition, are seen in emission . The emission lines allow us to determine the gas density ( n ~ 1500-3000 cm -3 ) and CO column densities [ N (CO) ~ 7.9 × 10 15 -2.8 × 10 17 cm -2 ] using a standard large velocity gradient analysis. By using both the o-H 2 18 O and o-H 2 O absorption lines, we are able to constrain the column-averaged o-H 2 O abundances in each line-of-sight cloud to within about an order of magnitude. Assuming the standard N (H 2 )/ N (CO) ratio of 10 4 , we find N (o-H 2 O)/ N (H 2 ) = 8.1 × 10 -8 to 4 × 10 -7 for three clouds with optically thin water lines. In three additional clouds, the H 2 O lines are saturated, so we have used observations of the H 2 18 O ground-state transition to find upper limits to the water abundance of 8.2 × 10 -8 to 1.5 × 10 -6 . We measure the OH abundance from the average of the 1665 and 1667 MHz observations and find N (OH)/ N (H 2 ) = 2.3 × 10 -7 to 1.1 × 10 -6 . The o-H 2 O and OH abundances are similar to those determined for line-of-sight water absorption features toward W51 and Sgr B2 but are higher than those seen from water emission lines in molecular clouds. However, the clouds toward W49 have lower ratios of OH relative to H 2 O column densities than are predicted by simple models, which assume that dissociative recombination is the primary formation pathway for OH and H 2 O. Building on the 2002 work of Neufeld and coworkers, we present photochemistry models including additional chemical effects, which can also explain the observed OH and H 2 O column densities, as well as the observed H 2 O/CO abundance ratios.
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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 | 0.001 | 0.000 |
| Science and technology studies | 0.001 | 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) | 0.001 | 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 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".