Specview Cookbook for Combining Low dispersion Spectra

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Specview Cookbook for Combining Low dispersion
Spectra

• M. Smith, I. Kamp, and I. Busko
• Space Telescope Science Institute

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In this tutorial we will combine five IUE and
HST spectra as follows

• Scale fluxes, trim spectrum ends as needed
• Coadd spectra and plot the coaddition
• (temporarily) detrend the spectrum
• FFT-filter the spectrum
• Coplot the FFT and coadded spectra
• Review relevant windows
• Save data files

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First, get into Specview

• Click on empty applet link at
• http//specview.
• stsci.edu/applet

(spectrum plotting window)
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Approve two security certificates
(first time only)

• Click on always, then yes, for the two
  certificates
• offered.

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• To read in data files Click on File,
• Read from File
• tabs and

highlight, open files, one at a time.
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Once files are loaded in

• open tab Coplot/process
• tab (arrow)

and open Processing Window.
processing window
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Next activate the windows contents

• Highlight all
  spectra of interest
• (left-mouse shift)
• Click on Process

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• Up comes the
• Processing
• Window
• for these five spectra

and at the same time
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the two panel plot
(For now ignore upper panel)

• Plotting window shows the 5 coplotted spectra.

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To modify scale factors click to open cell and
enter new factor, click cell shut. (guess values
trial error!)
Enter scale Factors and click Execute.
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Rescaled

• Continue changing scale factors as necessary
• and click Execute to plot.

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• Two-panel plot shows before/after
• effects of inter alia scaling of the spectra.

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• Now work through red/blue wavelength limits
• in the same way. When done click Execute.

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Upper rescaled spliced
Lower raw data coplotted, no action

• Inspect the resulting dual panel plots.

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Lets go to single panel, click on Execute this
Step
Click Resample tab
Accept default (finest grid sampling) or input
your own value.
and Execute.
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• The coplotted, scaled trimmed spectra

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Proceed to Coadd step
(last chance to exclude spectra!)
Click on Execute this Step Execute.
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Our trimmed, coadded spectrum
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Digression-1

• At this point you may wish to
• save your coadded spectrum.
• (Click on File/Save as
• tab over plotting window)

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Digression-2

• Click on File/Save As in spectrum window.

Enter saved coadded spectrum file name.
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Now proceed to Detrend step

• Click on Execute this Step Execute.

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(Detrend step is transient used internally for
next (filter) step.)

• Type in wavelength near left end of spectrum.
• Click in cell (now pink) and enter value. Click
  cell shut.

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Work on flux of left end

• Enter flux through which you want the working
  spectrum to be detrended and again click shut.

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Completed Detrend window

• Make sure Auto Compute is
• clicked off and Click Execute.

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The temporarily detrended spectrum
To FFT filter, click Filter in processing box.
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FFT filter processing

• Click Execute this Step

and Execute.
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Need to change the FFT filter? UNCLICK AUTO
CUTOFF!

• Enter a new cutoff frequency in box, Click
  Execute.

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The resulting Brault-White FFT filter
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and the FFTd spectrum
Save this spectrum as for slide 18 before if you
wish.
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• Save the filtered spectrum as before if you wish.

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If necessary, read in coadded spectrum
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• To coplot coadded FFT spectra, click Coplot,
  
• highlight processed spectra, and click Plot.

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Final coplot of the spectra
Coadded Filtered
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• We are now done.
• Note we can save the result spectrum as an ascii
  file. The plots cannot be saved except as screen
  shots.