<i>Herschel</i>/HIFI observations of interstellar OH<sup>+</sup>and H<sub>2</sub>O<sup>+</sup>towards W49N: a probe of diffuse clouds with a small molecular fraction
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Bibliographic record
Abstract
We report the detection of absorption by interstellar hydroxyl cations and water cations, along the sight-line to the bright continuum source W49N. We have used <i>Herschel<i/>'s HIFI instrument, in dual beam switch mode, to observe the 972 GHz <i>N<i/> = 1–0 transition of OH<sup>+<sup/> and the 1115 GHz 1<sub>11<sub/>–0<sub>00<sub/> transition of ortho-H<sub>2<sub/>O<sup>+<sup/>. The resultant spectra show absorption by ortho-H<sub>2<sub/>O<sup>+<sup/>, and strong absorption by OH<sup>+<sup/>, in foreground material at velocities in the range 0 to 70 km s<sup>-1<sup/> with respect to the local standard of rest. The inferred OH<sup>+<sup/>/H<sub>2<sub/>O<sup>+<sup/> abundance ratio ranges from ~3 to ~15, implying that the observed OH<sup>+<sup/> arises in clouds of small molecular fraction, in the 2–8% range. This conclusion is confirmed by the distribution of OH<sup>+<sup/> and H<sub>2<sub/>O<sup>+<sup/> in Doppler velocity space, which is similar to that of atomic hydrogen, as observed by means of 21 cm absorption measurements, and dissimilar from that typical of other molecular tracers. The observed OH<sup>+<sup/>/H abundance ratio of a few ×10<sup>-8<sup/> suggests a cosmic ray ionization rate for atomic hydrogen of 0.6–2.4×10<sup>-16<sup/> s<sup>-1<sup/>, in good agreement with estimates inferred previously for diffuse clouds in the Galactic disk from observations of interstellar H<sub>3<sub/><sup>+<sup/> and other species.
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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) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 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 | 0.001 |
| 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 it