Probing the Atmospheres of Hot DA White Dwarfs with O VI
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Bibliographic record
Abstract
We present an abundance analysis of the oxygen detected in the FUSE spectra of three hot white dwarfs with effective temperatures lower than 50,000 K: GD984, REJ1032+532, and REJ2156−543. The FUSE data show unexpectedly strong O VI λλ1032 and 1038 lines. We demonstrate that stellar atmosphere models with homogeneous oxygen abundances neither reproduce the O VI doublet nor the Extreme Ultraviolet Explorer data. Our models show that some O VI ions are formed by photoionization in the upper layers of the atmosphere and are sensitive to the EUV opacity of O III and O IV at lower depths. Based on these findings we compute models that include an oxygen abundance that varies as a function of depth. We show that the oxygen abundance should be lower at depths where the O III and O IV ions predominate in order to reduce the opacity in the EUV range, and it should be higher in the upper layers to allow the production of strong O VI lines. Our results provide one of the best evidence that the abundance of an element heavier than hydrogen is stratified in the atmospheres of white dwarfs. 1. O VI in the Atmospheres of Hot White Dwarfs The detection of the O VI lines at 1031.9261 A and 1037.6167 A in the FUSE spectra of GD 984, RE J1032+532, and RE J2156−543 indicates that a mechanism must be at work in the atmosphere of these stars in order to neutralize the effect of the downward oxygen diffusion. If left uninhibited, the gravitational settling can empty the white dwarf atmospheres of its oxygen content on very short time scales. For such hot stars, however, the outward radiative forces are strong enough that they can counteract the effect of the gravity and support traces of oxygen in their atmospheres. The radiative levitation theory predicts that the equilibrium distribution of oxygen in the atmospheres of these stars is not homogeneous according to models computed by Schuh (2000). The predicted oxygen abundance varies as a function of depth, because the radiative forces depend on the oxygen ionization Primary affiliation: Department of Physics and Astronomy, University of Victoria, P.O. Box 3055, Victoria, BC V8W 3P6, Canada
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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) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 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 | 0.000 |
| 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 it