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XMM-Newton Science Analysis System


omgsource (omgsource-1.2.18) [xmmsas_20050815_1803-6.5.0]

Meta Index / Home Page

The spectrum-selection window

This window is shown in Figure 2.

Figure 2: Spectrum-selection window

When the cursor is moved across the image (using the left-mouse button) a profile, from the cursor-position upwards to the height of the spectrum extraction-region height, is drawn at the bottom of the image. A new spectrum is selected by centering the cursor (either by moving the mouse or by using the arrow keys on the right of the key-board) over the approximate centre of the corresponding zeroth-order feature and either clicking the left-mouse button or hitting the return key. Please note that if any of the centroiding buttons are enabled, the extraction region coordinates will differ from those initially selected (these buttons are initially disabled.) The extraction region is plotted below the image and its position and dimensions are stored in the table in the upper-left corner of the window. A selected extraction region can be discarded by placing the cursor within the spectrum-extraction region and either pressing the right mouse-button or hitting the Delete key.

The user can change the width and height of the extraction rectangle and the widths and offsets of the left and right background-extraction rectangles (within certain limits). The left and right background extraction offsets are the distances (pixels) from the left and right sides of the inner spectrum extraction-region, respectively.

The computation of a spectrum is done using the SAS task omgrism, and omgsource produces a source-list file containing two sources, the zero and first order spectra, for input to omgrism. The program allows the approximate y cursor-coordinate of the zeroth-order spectrum to be either fixed at the cursor-position (y Zero-order button unchecked, or refined using a centroiding algorithm (yZero-order button checked. Since the wavelength scale of the first-order spectrum is set using the y-coordinate of the zeroth-order spectrum, the accuracy of the scale is therefore determined by the accuracy of the y-coordinate.

Likewise, the approximate x cursor-coordinate of the first-order spectrum can be either fixed at the cursor-position (x First-order button unchecked, or refined using a centroiding algorithm (x First-order button checked. The reason why the first-order x coordinate is used instead of the zeroth-order coordinate, is that there could be a shift of several pixels between the two positions.

NOTE THAT WHEN OMGRISM ANALYSES A SOURCE-LIST PRODUCED BY OMGSOURCE, NO CHECKING IS DONE ON THE SOURCE PARAMETERS- IT IS UP TO THE USER TO CHECK THE VALIDITY OF ANY SPECTRUM PRODUCED