FA-55642 / Astronomical coordinate conventions / Member archive
Air vacuum line coordinate: Frequency is computed from air wavelength without refractive-index conversion · case 02
The adapter reports an incorrect vacuum frequency while other fields remain valid.
Case contract
The supplied index n=a/b is a positive rational greater than zero. This finite constant-index adapter maps air wavelength to vacuum by multiplication n. Frequency belongs to vacuum wavelength; flux densities change inversely with wavelength-bin Jacobian. It does not model dispersion of refractive index. Output fields are defined by: vacuum_wavelength = d['L']*d['a']/d['b']; air_wavelength = d['L']*d['b']/d['a']; vacuum_width = d['width']*d['a']/d['b']; vacuum_density = d['F']*d['b']/d['a']; vacuum_frequency = d['c']*d['b']/(d['L']*d['a']); line_displacement = d['L']*(d['a']-d['b'])/d['b']
Why this case matters
Catalog, detector, sky-coordinate, and spectroscopy adapters must preserve the association between numeric coordinates and their declared reference conventions.
One recorded failure
Sample boundary fixtureThis sample comes from the broken implementation of a controlled reproducer.
| Boundary fixture | Actual | Expected | Outcome |
|---|---|---|---|
| astronomical fixture 0 | {"air_wavelength": 7.333333333333333, "line_displacement": 5.5, "vacuum_density": 4.0, "vacuum_frequency": 10.909090909090908, "vacuum_wavelength": 16.5, "vacuum_width": 6.0} | {"air_wavelength": 7.333333333333333, "line_displacement": 5.5, "vacuum_density": 4.0, "vacuum_frequency": 7.2727272727272725, "vacuum_wavelength": 16.5, "vacuum_width": 6.0} | Failed |
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