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8.2 Plotting Line-by-Line Spectra

For both IUESIPS and NEWSIPS (including SIHI files) you can plot the data using the routine SRPLOT. (For those users who remember LBL and IUEIM, SRPLOT can do everything those procedures could do.) SRPLOT will read in the requested portion of the data and do whatever summing (in either the wavelength or spatial directions) the user wishes. The calling sequence is as follows:


FILENAME is the name of the line-by-line file to be read. If FILENAME is entered without any other parameters, the 18 lines centered on the spectrum (large aperture for SILO files) will be displayed.
line will be the line number(s) desired. You can enter a single number to extract a single line , two numbers to designate a range of lines to extract, or a vector with more than two line numbers, in which case those exact lines will be extracted. To extract all lines enter an unreasonable line number (e.g., -1). To select the lines encompassing the large aperture spectrum, enter 0. Note that lines are numbered starting with 1 (the earliest version of this program used the IDL indexing convention of starting with 0).
sow (Sample Or Wavelength) is similar to the Line parameter, but refers to sample numbers or wavelengths. The program will be able to figure out whether you have given sample numbers or wavelengths.
h will be either the FITS header or the IUESIPS scale factor record.
x will be either wavelengths or line numbers, depending on what keywords were set.
f will be fluxes.
q will be $\nu$ flags for NEWSIPS data, or $\epsilon$ flags for IUESIPS data.
across This keyword, if set, tells the program that you wish to take a cut ACROSS the dispersion. Thus all the samples extracted will be summed. Your X parameter will be returned as line numbers.
along This keyword, if set, tells the program that you wish to take a cut ALONG the dispersion. Thus all lines extracted will be summed. Wavelengths will be returned in X.
order For SIHI files, program displays lines centered on specified order number, and halfway between adjacent orders. Default = 100 if no other parameters are specified. Can be used with keyword ACROSS to assign wavelengths but should not be used with ALONG.

See Table 8.1 for examples.


Table 8.1: SRPLOT Examples
Low Dispersion Examples
srplot,imaget,-1,-1 Plot entire line-by-line file.
srplot,imaget,[45,55],-1 Plot lines 45 through 55.
srplot,imaget,-1,[1300,1700] Plot the region between 1300 and 1700 angstroms.
srplot,imaget,[45,55],-1,/along Sum up lines 45 through 55 and plot the resulting vectors.
srplot,imaget,[45,55],-1,h,w,f,nu,/along Same as above, but extract the vectors for use in your IDL session.
srplot,imaget,-1,[300,400],/across Sum up samples 300 through 400 and plot the resulting cross-section.
srplot,imaget,[30,35,40,45,50],-1 Plot lines 30, 35, 40, 45, and 50.
srplot,imaget,[30,40],[1400,1500], $
Find the average flux in the region of lines 30-40, 1400-1500 angstroms.
High Dispersion Examples
srplot,imaget,order=75 display order 75.
srplot,imaget,[306,311],order=98,/along plot order 98 but only sum over lines 306 to 311.
srplot,imaget,[300,320],[200,250] display a pseudo 3-d plot of the region between lines 300 to 320 and columns 200 to 250.
srplot,imaget,-1,[200,300],/across plot cross-section of spectrum summing over columns 200 to 300.

The $\nu$ flags will be coalesced if any summing is done. In other words, all bit values will be preserved. For IUESIPS data the lowest $\epsilon$ value will be kept.

Note that it is possible to sum up the entire image if both the /across and the /along keywords are set--resulting in scalar values. You'll be warned if you attempt such things but you will not be stopped.

For NEWSIPS data, a notation will be made in the HISTORY section of the output FITS header vector describing what was extracted and what summing was done, if any.

SRPLOT uses NSPLOT to plot vector results (in the case of summing, or if you specified only one line or sample).

SRPLOT displays two-dimensional results with a procedure called PSEUDO3D. You can run this procedure interactively if you wish, once you have appropriate arrays in your IDL session. Please run DOC_LIBRARY for more information.

next up previous contents
Next: 8.3 Old Line-By-Line Files Up: 8 REDUCING SPATIALLY-RESOLVED DATA Previous: 8.1 Reading Line-By-Line Files