SPECPR Users’ Manual Page 8-f5.1 F5: Continuum Removal Alias: cont[rem] The f5 continuum removal is an old algorithm that has been superseded in most cases by newer routines such as f12 (cubic spline) and f44 (segmented upper hull). However, it does have an advantage in that it removes a continuum of a specific shape given by the user in the form of a spectrum. To enter the routine, type f5. The directions are fairly simple. The routine fits a given continuum to a spectrum. The routine will prompt for the continuum and spectrum, as well as the continuum points used for the fit. Basically, you select two channels and a straight line is generated through these two channels in both the given continuum and the spectrum. The continuum is modified by linearly changing its slope so that the same two channels on the continuum match the values in the spectrum. Once the fit is complete, the spectrum is divided by the modified continuum. First, you will be instructed to enter the two channels for which you want to match the continuum. Usually that will be on each side of an absorption band. Enter two values to which continuum is to be matched followed by h, a, or n representing units of channel, wavelength, and energy (inverse wavelength, and the wavelength file id and record number. For example: 12 33 h V36 or 1.2 1.65 a V36 would be equivalent if channel 12 = wavelength 1.2 and channel 33 = wavelength 1.65. The wavelength set is then V36. The two points can be entered in whatever units are convenient for you, in free format (spaces between numbers, no commas). The wavelength file is read, and the two values entered are correlated with the appropriate channel in the wavelength set. You can exit the routine here if you wish with an e or x command. Next, enter the spectrum file id and record number, e to include errors followed by the continuum file id and record number. Type e or x to exit the routine. The message on the CRT will say "WORKING" when you hit the return key after entering the information. The title of the files used will be printed on the CRT as they are accessed by the program. The error file with the spectrum is accessed if it was requested. The continuum spectrum is scaled to the spectral data at the two given points by calculating a scaled slope and an intercept (or vertical offset) and converting each data point of the continuum to the scaled continuum through the relationship Y = mx + b where Y is the scaled continuum, m is the slope, x is the original continuum value at a given channel, and b is the intercept. The spectrum is then divided by the scaled continuum. The errors are scaled by a factor of (scaled spectrum ÷ original spectrum). Finally, the title and history are made and control is transferred back to the main program to write the file. Original author: Lucy Mcfadden