A New Generation of Cool White Dwarf Atmosphere Models. III. WD J2356–209: Accretion of a Planetesimal with an Unusual Composition
Bibliographic record
Abstract
Abstract WD J2356−209 is a cool metal-polluted white dwarf whose visible spectrum is dominated by a strong and broad sodium feature. Although it was discovered nearly two decades ago, no detailed and realistic analysis of this star had yet been realized. In the absence of atmosphere models taking into account the nonideal high-density effects arising at the photosphere of WD J2356−209, the origin of its unique spectrum had remained nebulous. We use the cool white dwarf atmosphere code presented in the first paper of this series to finally reveal the secrets of this peculiar object and details about the planetesimal that polluted its atmosphere. Thanks to the improved input physics of our models, we find a solution that is in excellent agreement with the photometric observations and the visible spectrum. Our solution reveals that the photosphere of WD J2356−209 has a number density ratio of , which is the highest ever found in a white dwarf. Since we do not know how long ago the accretion episode stopped (if it has), we cannot precisely determine the composition nor the mass of the accreted planetesimal. Nevertheless, all scenarios considered indicate that its composition is incompatible with that of chondrite-like material and that its mass was at least 1021 g.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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 | 0.002 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.002 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.002 | 0.001 |
| Open science | 0.002 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 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".