SMART Defringing - Method

The IRS Defringing algorithm is explained at Defringing-Theory.

N.B. There is also a defringing manual at IRS Defringe?. This manual is not recommended for new users.

IRSFRINGE was developed by Fred Lahuis as an easy-to-use tool to remove instrumental fringes from Spitzer-IRS data.

To invoke the IRS Defringe GUI from SMART, the IDEA window must be open. Set the dataset for defringing as "Prime".

(Go to Store for more information on making the data set Prime.)

On the SMART IDEA window click on the Fns button, then click Defringe, then Defringe (IRS). The following windows will then appear :

The left hand window is the main IRSFRINGE window. The diagonal lines linking orders of different modules are due to plotting every order and module at the same time.

The right hand window "defringing results" shows the spectrum in white and green and the spectrum continuum in red.

Below that the sine curve fit that the IRS Defringe? algorithm performs on each order is shown.

This window changes for each order, and the last window shown is the last order IRS defringing was performed on.

• Select which module to start with on the right side of the window (i.e. LL, SH, LH).

  SL will never need defringing, its resolution is too low to show instrumental fringes.

• Select the BCD, Order, and SlitPos (slit position). As many Orders up to all Orders may be selected. The defringer will run on every Order chosen.
• Choosing cycles is important. Leave the second window blank when only one cycle is in use:
  For LL, cycle will be about 750
  For SH, cycle will be about 3500
  For LL, cycles will be about 3000 and 8000
  These values are approximate and may have to be altered from spectrum to spectrum.

  A certain amount of experimenting with values is required to use this tool properly.

• On the "fit" GUI button there is the choice of auto or manual. With manual, the tolerance and number of fringes must be chosen.
• The five buttons above the plot are :

  "Replot"

  replots the module, BCD, order, and Slitpos chosen. |

  "Find cycle"

  returns the approximate values for cycle as shown above. |

  "Defringe test"

  runs the IRS defringe algorithm. |

  "Save defringed"

  saves the current defringed spectrum in favor over the original fringed spectrum. |

  "Exit with Current"

  exits with the current spectrum. |

• Clicking "Degringe test" with the manual fit selected produces these four windows :
  (Selecting "auto" fit will only produce the first two windows.)

|Results of the Defringe Test :

1. In the first window "IRSFRINGE", the defringed spectrum is shown in red, the fringed (or "previous", as it is called) is shown in green.
2. In the second window, "defringing results", the original spectrum is shown in white, its continuum is in red, and the defringed spectrum is shown, raised for clarity, in green.

   Seven fringes were found in this example, as the sine curve plot shows.

3. The third window "Fringes found", shows a more intricate plot of the sine wave of fringes in wavenumber, and it also shows (the vertical green lines) where the fringes were found.
4. The fourth window "Fringe details" has two plots :
   1. The upper is amplitude v. fringe period (cm -1) with CHI^2 superimposed.
   2. The lower is amplitude v. optical thickness, with fringes shown in green.

• The buttons to the right hand side of the plot in the IRS Defringe window are the same as those in the IDEA window.

  Full details at SMART IDEA Buttons - Positional Description.

• A certain amount of experimenting will be necessary in order to obtain a full understanding of how the GUI works.

  IMPORTANT - Remember that nothing is saved unless the "Save Defringed" button on the IRS Defringe window is pressed.

• The algorithm is explained on the Defringing-Theory page.