Radiative levitation: a likely explanation for pulsations in the unique hot O subdwarf star SDSS J160043.6+074802.9
Bibliographic record
Abstract
\n Context. SDSS J160043.6+074802.9 (J1600+0748 for short) is the only hot sdO star\nfor which unambiguous multiperiodic luminosity variations have been\nreported so far. These rapid variations, with periods in the range from ~60 s to ~120 s, are best qualitatively explained in terms of\npulsational instabilities, but the exact nature of the driving mechanism\nhas remained a puzzle.\n Aims. Our primary goal is to examine quantitatively how pulsation modes can\nbe excited in an object such as J1600+0748. Given the failure of \nuniform-metallicity models as well documented in the recent Ph.D. thesis of\nC. Rodríguez-López, we consider the effects of radiative levitation\non iron as a means to boost the efficiency of the opacity-driving\nmechanism in models of J1600+0748.\n Methods. We combine high sensitivity time-averaged optical spectroscopy and full\nnonadiabatic calculations to carry out our study. In the first instance,\nthis is used to estimate the location of J1600+0748 in the log\n$g-T_{\\rm eff}$ plane. Given this essential input, we \npulsate stellar models consistent with these atmospheric parameters. We\nconstruct both uniform-metallicity models and structures in which the\niron abundance is specified by the condition of diffusive equilibrium\nbetween gravitational settling and radiative levitation.\n Results. On the basis of NTLE H/He synthetic spectra, we find that the target\nstar has the following atmospheric parameters: log g = 5.93 ± 0.11, Teff = 71 070 ± 2725 K, and log N(He)/N(H) =\n-0.85 ± 0.08. This takes into account our deconvolution of the\nspectrum of J1600+0748 as it is polluted by the light of a main sequence\ncompanion. We confirm that uniform-metallicity stellar models with Z\nin the range from 0.02 to 0.10 cannot excite pulsation modes of the kind\nobserved. On the other hand, we find that the inclusion of radiative\nlevitation, as we implemented it, leads to pulsational instabilities in a\nperiod range that overlaps with, although it is narrower than, the\nobserved range in J1600+0748. The excited modes correspond to low-order,\nlow-degree p-modes.\n Conclusions. We infer that radiative levitation is a likely essential ingredient\nin the excitation physics at work in J1600+0748.\n
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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 | 0.001 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 0.001 |
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".