5.7.4 Rectify

The purpose of this step is to remove from the data (divide by) a polynomial baseline, in preparation for Fourier filtering.

 

The control panel for this processor module is show below. The default is to run it in “Auto compute” mode, in which a linear trend is computed based on the averaged data values at each end of the flux and wavelength arrays.

 

By unchecking the Auto compute check box, one can instead change the polynomial order, and add / remove specific values of flux density and wavelength from the table of data points to be modeled by the polynomial.

 

Values entered in the table are assumed to be in units of Angstrom and photon/s/cm**2/Angstrom.
 

 
 

Use the Add range button to add a new data point by selecting a range of wavelengths on the spectrum display window, using the graphics cursor in the following way:

Click the Add range button once; a message saying “Click cursor to mark one end of the range’s end points” will instruct you to click the graphics cursor on the first wavelength used to define the range, as in the next picture.

 

Move the graphics cursor to the desired wavelength and click the mouse there. A second message saying “Click cursor again to mark other end point” now will remind you to click with the graphics cursor on the second wavelength that defines the range.

 

Once the second wavelength is defined, the wavelength and flux values are averaged inside the wavelength range just defined, and the averages are added to the table. If then the Execute button is pressed, the display will be updated with a depiction of the new wavelength range as a blue horizontal segment, as in the next picture.

 

Note that there is no need to actually press the Execute button every time a new wavelength range is added to the table of data points. This is done just to update the spectrum plot the first time. As other ranges are added or removed, the display will update itself automatically.

Use the Add point button to add a new data point by directly typing in values of wavelength and flux.

Use the Remove point button to remove an existing data point. First, select the desired data point to be removed by clicking on the table. The data point removal functionality is disabled when only two data points are present.

The numerical fields can be populated by just typing on then, or by clicking the cross hair cursor over the plot window at each desired point. See Section 5.7.1.1 on how to do that.

The Polynomial order selector allows the selection of the polynomial order used to build the rectification continuum. This value will be limited to a maximum of one less the current number of data points. Note that, in some platforms, the typed value will be entered only after hitting the Enter/Return key.

Note that no default values are available in this module. Values will change as a function of which steps were run before in the processing pipeline, and what parameters where used in each step.

Note also that the parameters must be expressed in photlam (photons/s/cm^2/Angstrom) and Angstrom units. See in Sec. 5.8 how the display can be reconfigured appropriately to display data in these units. Note also that the rectified data will display correctly (with a constant baseline of zero) only when the display units are set to photlam and Angstrom.

This module acts on a single spectrogram only. In case of multiple spectra being combined, the Coadd Module (Sec. 5.7.3) must be run before this module can be activated.