air_to_vac

specutils.utils.wcs_utils.air_to_vac(wavelength, scheme='inversion', method='Morton2000', co2=None, precision=1e-12, maxiter=30)[source]

Converts air to vacuum wavelengths using different methods.

Parameters:
wavelengthQuantity object (number or sequence)

Air wavelengths with an astropy.unit.

schemestr, optional

How to convert from vacuum to air wavelengths. Options are:

  • ‘inversion’ (default) - result is simply the inversion (1 / n) of the refraction index of air. Griesen et al. (2006) report that the error in naively inverting is less than 10^-9.

  • ‘Piskunov’ - uses an analytical solution derived by Nikolai Piskunov and used by the Vienna Atomic Line Database (VALD).

  • ‘iteration’ - uses an iterative scheme to invert the index of refraction.

methodstr, optional

Only used if scheme is ‘inversion’ or ‘iteration’. One of the methods in refraction_index, default is ‘Morton2000’

co2number, optional

Atmospheric CO2 concentration in ppm. Only used if scheme=’inversion’ and method=’Ciddor1996’. If not given, a default concentration of 450 ppm is used.

precisionfloat

Maximum fractional value in refraction conversion beyond at which iteration will be stopped. Only used if scheme=’iteration’.

maxiterinteger

Maximum number of iterations to run. Only used if scheme=’iteration’.

Returns:
vac_wavelengthQuantity object (number or sequence)

Vacuum wavelengths with the same unit as wavelength.