A Survey of O<scp>vi</scp>Absorption in the Local Interstellar Medium
Bibliographic record
Abstract
We report the results of a survey of O VI λ1032 absorption along the lines of sight to 25 white dwarfs in the local interstellar medium (LISM) obtained with FUSE . We find that interstellar O VI absorption along all sight lines is generally weak, and in a number of cases, completely absent. No O VI absorption was detected with significance greater than 2 σ for 12 of the 25 stars, where the 1 σ uncertainty is ~4 mÅ, equivalent to an O VI column density of ~3 × 10 12 cm -2 . Of the remaining stars, most have column densities N (O ) < 10 13 cm -2 , and no column densities exceed 1.7 × 10 13 cm -2 . For lines of sight to hot ( T eff > 40,000 K) white dwarfs, there is some evidence that the O VI absorption may be at least partially photospheric or circumstellar in origin. We interpret the "patchy" distribution of O VI absorption in terms of a model in which O VI is formed in evaporative interfaces between cool clouds and the hot, diffuse gas in the Local Bubble (LB). If the clouds contain tangled or tangential magnetic fields, then thermal conduction will be quenched over most of the cloud surface, and O VI will be formed only in local "patches" where conduction is allowed to operate. We find an average O VI space density in the LISM of 2.4 × 10 -8 cm -3 , which is similar to, or slightly larger than, the value in the Galactic disk over kiloparsec scales. This local density implies an average O VI column density of ~7 × 10 12 cm -2 over a path length of 100 pc within the LB. The O VI data presented here appear to be inconsistent with the model proposed by Breitschwerdt & Schmutzler, in which highly ionized gas at low kinetic temperature (~50,000 K) permeates the LB. Our survey results are consistent with the supernova-driven cavity picture of Cox & Smith for the LB, and in particular, the recent model by Cox & Helenius for the creation of cool clouds in the LB by magnetic flux tubes and their subsequent magnetic shielding from conduction.
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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 | 0.002 | 0.001 |
| 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) | 0.001 | 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".