Recent observational and theoretical studies of the classical nova outburst<sup>1</sup>This review is part of a Special Issue on the 10th International Colloquium on Atomic Spectra and Oscillator Strengths for Astrophysical and Laboratory Plasmas.
Bibliographic record
Abstract
Many facets of astrophysics are captured in classical novae (CNe) eruptions, making these systems unique laboratories to investigate several poorly understood processes, many in real time. CNe may also be related to the super-soft sources, the likely progenitors of SN Ia explosions. Spectra of CNe ejecta, from X-ray to infrared (IR) wavelengths, are remarkable for the changing elemental and ionic content as the ejecta temporally evolves — often exhibiting a variety of low-energy permitted lines of CNO and Fe II, high ionization lines, e.g., [Fe VIII] λ 6078 Å, and IR “coronal” lines (few 100 eV transitions) of metals such as Ne, Si, S, and Ar. At higher energies, X-ray and UV emission in CNe comes from the nuclear burning of residual accreted material on the white dwarf surface after the initial outburst; this emission directly probes processes powering the post-outburst evolution of the white dwarf and the ejecta. Some nova systems are observed to form dust, making CNe one of the known in situ stellar sources of dust grains. However, from a theoretical standpoint the interpretation of the emission line spectra, the derivation of metal abundances and estimates of ejecta mass are vexed by limited and (or) uncertain atomic and molecular data that is becoming increasingly acute, as spectral resolution and wavelength coverage expands into heretofore new observational phase space. Here we highlight IR observations of select CNe, including V2467 Cygni and V2361 Cygni, studied with the NASA Spitzer telescope and contemporaneously with ground-based optical spectroscopy as well as Swift, Chandra, and XMM-Newton spectrophotometry. We discuss new paradigms derived from photoionization models, recent issues associated with ejecta abundances derived from hydrodynamical codes simulating the nova outburst, and future challenges.
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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 | 0.003 | 0.006 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.002 | 0.002 |
| Science and technology studies | 0.000 | 0.002 |
| Scholarly communication | 0.002 | 0.003 |
| Open science | 0.001 | 0.002 |
| Research integrity | 0.001 | 0.002 |
| Insufficient payload (model declined to judge) | 0.004 | 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".