def air2vacMortonIAU(wl_air):
    """Take an input air wavelength in Angstroms and return the vacuum
    wavelength.

    Formula taken from
    https://www.astro.uu.se/valdwiki/Air-to-vacuum%20conversion
    """
    s = 1e4 / wl_air
    n = 1 + 0.00008336624212083 + (0.02408926869968 / (130.1065924522 - s**2))\
        + (0.0001599740894897 / (38.92568793293 - s**2))
    return wl_air * n