Air to vacuum wavelength converter

I can imagine scenarios where people get wavelengths from FITS files where keywords allow air and vacuum wavelengths, e. Usually space-based instruments tend to have FITS with vacuum wavelengths, while ground-based instruments have in air wavelengths. Comparing or using both often needs a conversion. I'll try to start a PR to implement this in specutils.

Given the above consensus that this belongs to spectutils for now, I'm closing the issue here. Feel free to reopen if you think this interpretation of the conversation is incorrect. Skip to content. Star 3k. New issue. Jump to bottom. Labels Close? Feature Request units. Copy link. The notebook has a brief historical discussion and references. Kia ora koutou, Benjamin Alan Weaver.

Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment. Linked pull requests. You signed in with another tab or window. Reload to refresh your session. Ciddor assumes a CO2 concentration of ppm, while Edlen, and Peck and Reeder have assumed ppm. The target precision beyond which iteration should be stopped; default is 1e In contrast to airtovac and vactoair , which only transform the wavelength axis, this function converts the wavelength axis and interpolates the shifted spectrum to retain the input wavelength axis.

Due to the shift, a fraction of the spectrum is lost on one side, while there is no valid information on the other. Therefore, the function returns both a new flux array obtained by linear interpolation and an array of valid indices, i. Linear interpolation of the spectrum can affect its noise properties. This function does nothing to prevent or correct for that effect. The opposite is true otherwise. If True, the now deprecated function airtovac and vactoair will be used.

Otherwise default , airtovac2 and vactoair2 will be used with default settings. The conversion implemented here is based on the older formulae given by Edlen Furthermore, it seems that wave numbers in air are used, where vacuum wave numbers should be used, which, however, produces only a second-order deviation.

Consider using airtovac2 instead. Consider using vactoair2 instead. Navigation index modules PyAstronomy 0. Warning The function airtovac and vactoair are based on the formula by Edlen By default, the conversion specified by Ciddor are used. This function is a wrapper around the RefractiveIndexAV class. Parameters: wvl :float or array Wavelength in vacuum [A]. Returns: wvl : float or array Wavelength in vacuum [A].

Returns: wvl : float or array Wavelength in air [A].