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Note that there are two objects on the slit for this exposure. We are interested in the brighter of the two but could specify either for extraction.
Also, you may notice the relatively poor quality of the sky subtraction. Don't worry: this is the first attempt, and the final version used for spectral extraction will be much better. This iteration is only being used for object finding.
To select the left hand object, zoom in, place the cursor on the object of interest, and press the space bar. A cross will appear indicating the location of your selection, as shown here:
You can specify multiple locations, although there is no particular advantage to doing so. The software will take the median x-value of the selections and use that as an initial guess for the trace finding code. Once you have selected your object, press 'q' or click 'Done' and the code will trace your selection. When it has finished, it will plot up the results:
Here the solid line shows the object profile, and the dotted lines indicate the +/- 2 sigma boundaries of the fitted extraction aperture.
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