Improving accretion diagnostics for young stellar objects with mid-infrared hydrogen lines from JWST/MIRI
Bibliographic record
Abstract
Context . We present a comprehensive study of mid-infrared neutral hydrogen (H i ) emission lines in 79 nearby (d < 200 pc) young stars using the James Webb Space Telescope ( JWST ) Mid-Infrared Instrument (MIRI). This work extends accretion diagnostics to mid-infrared H i transitions, which are less affected by extinction and outflow emission compared to optical and near-infrared H i lines. Aims . We aim to identify mid-infrared H i transitions that can serve as reliable accretion diagnostics in young stars, and evaluate their utility in deriving physical conditions of the accreting gas. Methods . We identified and measured 22 H i transitions in the MIRI wavelength regime (5–28 µm) and performed LTE slab modelling to remove the H 2 O contribution from selected H i transitions. We examined the spatial extent of MIR H i emission and assessed contamination from molecular and jet-related emission. Results . We find that mid-IR H i line emission is spatially compact, even for sources with spatially extended [Ne II] and [Fe II] jets, suggesting minimal contamination from extended jet. Although Pfund α (H i 6–5) and Humphreys α (H i 7–6) are the strongest lines in the mid-infrared, they are blended with H 2 O transitions. This blending necessitates additional processing to remove molecular contamination, thereby limiting their use as accretion diagnostics. Instead, we identify the H i (8–6) at 7.502 µm and H i (10–7) at 8.760 µm transitions as better alternatives, as they are largely unaffected by molecular contamination and offer a more reliable means of measuring accretion rates from MIRI spectra. We provide updated empirical relations for converting mid-IR H i line luminosities into accretion luminosity for six different H i lines in the MIRI wavelength range. Moreover, a comparison of the observed line ratios with theoretical models shows that MIR H i lines offer robust constraints on the hydrogen gas density in accretion columns, n H = 10 10.6 to 10 11.2 cm −3 in most stars, with some stars exhibiting lower densities ( < 10 10 cm −3 ), approaching the optically thin regime.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.001 |
| 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".