SpecPro Tutorial

This tutorial is aimed at giving a quick overview of the capabilities of specpro.pro. It assumes that you have successfully downloaded the program and example files and have followed the installation instructions provided here.

Finding the redshift of a DEIMOS spectrum and saving it to file

  1. Go to the deimos_example directory.

  2. Start IDL, and at the prompt type: 
    specpro,70

    If the interface is too large for your monitor, close it and type:
    specpro,70, /small

  3. Adjust the contrast on the stamp images and 2D spectrum with the slider widgets. Note the obvious emission features in the binned 2D spectrum.

  4. Bin and smooth the 1D spectrum using the droplists underneath the 1D plot. This spectrum is fairly high S/N so not much binning is needed. A bin of 4 pixels, smooth of 3 seems to work well. Note that this is only for your visual benefit and does not influence any calculations the program does.

  5. Now turn on some lines. Clearly this spectrum has strong emission features, so select the "Emission" button underneath the "Bin" droplist. Feel free to turn on other lines as well.

  6. It is clear from the emission lines that the initial redshift guess (which comes from the zphot value in the info file) is close, but not quite high enough. To get the actual redshift, one approach is to use the "Enter redshift guess:" text field on the upper left of the interface, as well as the arrow buttons underneath it, which allow for coarse and fine redshift adjustments. Type 0.88 in the text field and press return. Not quite high enough - try using the arrows to get to the actual redshift of 0.89.

  7. Change the redshift to something incorrect, say 0.8.  Now select a galaxy template to overlay. This looks like a starburst galaxy, so select VVDS Starburst from the "Template:" droplist, located underneath the 1D spectrum.

  8. The program will automatically compute the six best redshift solutions when the template is selected. The best fit is set to the current redshift guess. Other solutions are in a droplist called "Select auto-z:". If the first solution displayed is wrong, try some of the others. In this case, it should have immediately found the correct redshift.

  9. Try zooming on the 1D plot. To do this, click, drag and release with the mouse (drawing a box) around the region of interest.

  10. You can also zoom on the 2D plot in the same way. Try it on the [OII] emission feature. This will pop up a separate window showing the unbinned zoom region, in which the characteristic shape of [OII] emission is evident.

  11. Now save the redshift to file. Click the "Like z" button under the 2D spectrum. This puts the current z guess in the output field in the lower part of the interface. Fill in the confidence, notes, and initials fields as well and click "Save Redshift". After saving it, take a look at the file to see the format. Any subsequent results saved to that file will be appended to it. It will also be the default saving location for the rest of the IDL session.

One more spectrum

  1. This example directory contains two sources, saved as slit 70 and slit 71. Switch to the slit 71 target by pressing the "Next " button in the upper left of the interface, or by typing 71 in the "Enter slit number: " text field and pressing return.

  2. The spectrum here shows few strong features, and the SED suggests that is a passive galaxy. Set the binning to 8 or 16 and the smoothing to 3 to bring out the weak absorption features. Note that the atmospheric A and B absorption features are prominent in this uncalibrated spectrum.

  3. Turn on the "Elliptical (subset)" lines. Because this appears to be a passive galaxy, select the VVDS Elliptical template. Note the first redshift guess displayed is probably not correct. Try some other guesses from the " Select auto-z solution: " droplist.

  4. Play with different templates and redshifts to see if you can convince yourself of the redshift, taking the SED into account as well. The answer here may not be 100% certain, but probably lies between 0.5 and 0.7.

  5. There is a faint serendipitous spectrum visible above the main target in the 2D image. Try extracting this source to 1D. To do this, place the cursor over the 2D image at the vertical position of the serendipitous spectrum. Click, drag horizontally (any amount, either direction) and release. This should trigger the reextraction, with the new 1D spectrum displayed. Saving the new 1D spectrum when prompted lets you then work with the serendipitous spectrum.