High-precision Atmospheric Characterization of a Y Dwarf with JWST NIRSpec G395H Spectroscopy: Isotopologue, C/O Ratio, Metallicity, and the Abundances of Six Molecular Species
Bibliographic record
Abstract
Abstract The launch of the James Webb Space Telescope (JWST) marks a pivotal moment for precise atmospheric characterization of Y dwarfs, the coldest brown dwarf spectral type. In this study, we leverage moderate spectral resolution observations ( R ∼ 2700) with the G395H grating of the Near-Infrared Spectrograph (NIRSpec) on board JWST to characterize the nearby (9.9 pc) Y dwarf WISEPA J182831.08+265037.8. With the NIRSpec G395H 2.88–5.12 μ m spectrum, we measure the abundances of CO, CO 2 , CH 4 , H 2 S, NH 3 , and H 2 O, which are the major carbon-, nitrogen-, oxygen-, and sulfur-bearing species in the atmosphere. Based on the retrieved volume mixing ratios with the atmospheric retrieval framework CHIMERA, we report that the C/O ratio is 0.45 ± 0.01, close to the solar C/O value of 0.458, and the metallicity is +0.30 ± 0.02 dex. Comparison between the retrieval results and the forward modeling results suggests that the model bias for C/O and metallicity could be as high as 0.03 and 0.97 dex, respectively. We also report a lower limit of the 12 CO/ 13 CO ratio of >40, being consistent with the nominal solar value of 90. Our results highlight the potential for JWST to measure the C/O ratios down to percent-level precision and characterize isotopologues of cold planetary atmospheres similar to WISE 1828.
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How this classification was reachedexpand
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) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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 itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, 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".