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Object-wise PSF-leakage correction zeros the same-object slope, not angular leakage; on v2 it raises τ0 by 52%

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Evaluación

Dificultad
5/5
Tiempo estimado
Más de una semana
Aptitud para principiantes
8/100
Tipo de issue
Error
Claridad
Necesita aclaración
Estado de actividad
Activo
Stack tecnológico
python

Línea de trabajo

The entry point is compute_PSF_leakage and the correction e_leak_corrected = e − α p, which fits α per SNR × size bin from the same-object galaxy–PSF slope. The payload does not name specific test files. Done would require a fit that targets angular leakage, validated on held-out stars, with per-bin α, errors and the global scalar persisted to the catalogue. This is design work and not a first-timer task.

Escrito por el modelo de indexación a partir del texto del issue.

Descripción

The object-wise PSF-leakage correction (compute_PSF_leakage → e_leak_corrected = e − α p) fits α from the same-object galaxy–PSF slope in SNR × size bins. Angular leakage is measured by ρ/τ at finite separation. These are different quantities, and on v2 they disagree in sign:

  • same-object slope (global scalar): −0.0030
  • the scalar that would zero first-bin τ0: +0.0058

So on v2, e_leak_corrected raises first-bin τ0 by 52% (5.25e-6 → 8.00e-6); on v1.4.6.3 it lowered τ0 by 59%. A perfect global same-object correction predicts the same 8.00e-6. The implementation itself checks out: the columns reconstruct to 4.6e-14, and the sign convention against stellar models is correct. Mechanism (verified): the same-object slope is a zero-lag mixture, α − β·Cov(p,δp)/Var(p) + η·Cov(p,q)/Var(p), where δp is the PSF ellipticity model error and q = p·δT_PSF/T_PSF the size-error term. The angular α, β, η, together with covariances from held-out stars, reproduce the measured slope: v2 −0.00310 predicted vs −0.00303 measured; v1.4.6.3 +0.0185 vs +0.0164. The size-error term is about −0.010 in both versions. v2's α is 2.5× smaller than v1.4.6.3's, so the sum turns negative. A per-object fit therefore can't isolate α, and a corrected v2 fiducial needs a fit that targets angular leakage.

Consequence: for v2, the _leak_corr columns are not a validated fiducial, so raw E is the reference.

Proposed:

  • make the target of compute_PSF_leakage explicit (object-wise vs angular on declared scales), and validate a correction on held-out stars before treating it as fiducial;
  • persist the fit diagnostics (per-bin α, errors, global scalar) with the catalogue;
  • label these columns as object-wise corrections in headers and docs.

Related: #382 (the trend-fit 1/σ⁴ weighting, negligible here at 5e-10), #413 (full a_ij / spin components).

Claude (Opus 5.5) on behalf of Cail

Lenguaje dominante
Python
Estrellas
2
Forks
5
Merge medio
1 d 1 h
PR fusionados (30 d)
26

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