<h1>The Cepheids of Centaurus A (NGC 5128) and Implications for <em>H<sub>0</sub></em></h1>
Bibliographic record
Abstract
A VI Wesenheit and period-colour analysis based on new OGLE observations reaffirms Ferrarese et al. discovery of 5 Type II Cepheids in NGC 5128.The distance to that comparatively unreddened population is d = 3.8 ± 0.4(σ x) Mpc.The classical Cepheids in NGC 5128 are the most obscured in the extragalactic sample (n = 30) surveyed, whereas groups of Cepheids tied to several SNe host galaxies feature negative reddenings.Adopting an anomalous extinction law for Cepheids in NGC 5128 owing to observations of SN 1986G (R V ≃ 2.4) is not favoured, granted SNe Ia may follow smaller R V .The distances to classical Cepheids in NGC 5128 exhibit a dependence on colour and CCD chip, which may arise in part from photometric contamination.Applying a colour cut to mitigate contamination yields d ≃ 3.5 Mpc (V-I 1.3), while the entire sample's mean is d ≃ 3.1 Mpc.The distance was established via the latest VI Galactic Wesenheit functions that include the 10 HST calibrators, which imply a shorter distance scale than Sandage et al. (2004) by 10% at P ≃ 25 d .HST monitored classical Cepheids in NGC 5128, and the SNe hosts NGC 3021 & NGC 1309, follow a shallower VI Wesenheit slope than ground-based calibrations of the Milky Way, LMC, NGC 6822, SMC, and IC 1613.The discrepancy is unrelated to metallicity since the latter group share a common slope over a sizeable abundance baseline (α = -3.34± 0.08(2σ), ∆[Fe/H]≃ 1).A negligible distance offset between OGLE classical Cepheids and RR Lyrae variables in the LMC, SMC, and IC 1613 bolsters assertions that VI -based Wesenheit functions are relatively insensitive to chemical abundance.In sum, a metallicity effect (VI ) is not the chief source of uncertainty associated with the Cepheid distance to NGC 5128 or the establishment of the Hubble constant, but rather it may be the admittedly challenging task of obtaining precise, commonly standardized, multiepoch, multiband, comparatively uncontaminated extragalactic Cepheid photometry.
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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 | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.019 | 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".