Check CUNIT for Angstrom or nm

[Roger Wesson]

ALFA assumes wavelengths are in Angstroms, and stops if no lines are found in the wavelength range. If the FITS header says the units are nm, ALFA should simply divide the line catalogue wavelengths by 10 and continue.

[Roger Wesson]

Implemented. CUNIT[13] is checked, and if nm is found, wavelengths are converted to A.
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