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Дата индексирования: Mon Apr 11 02:19:39 2016
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Поисковые слова: arp 220

Displaying spectra only

The tasks we discuss here allow you to make a line plot plot of a single spectrum averaged over some spatial region from a cube. There are two rather similar tasks with rather similar names; imspect and imspec. The latter offers more options, the former is easier to drive if you want something basic. We will give examples of both.

• We begin with imspect. The input cube can be in xyv or vxy order. This example plots a 3-point Hanning smoothed spectrum averaged over a small spatial region centred on the reference pixel.

  IMSPECT
  in=neon.xyv	Input cube
  region=relpix,box(-2,-3,2,3)	Spatial region to average over
  xaxis	Default to label x-axis in natural
  	spectral units (km/s or GHz)
  yaxis=average	Average over spatial region
  yrange	Auto-scale
  hann=3	Hanning smooth
  options	Unset
  device=plot/ps	PGPLOT device
  log	Unset; use to write spectrum to text file
  comment	Unset

  Note that imspect can also be used to plot the derivative of a spectrum (options=1der or options=2der) which may be useful for Zeeman enthusiasts.

  Now for imspec, which offers wider flexibility than imspect. It also plots spectra from a cube, but the cube can be in any order. It offers options to average or sum the data in RA-DEC, RA-VEL and DEC-VEL planes (keyword axes - see the help file for details) so that you get profiles along the velocity, DEC, and RA planes respectively. You can also convert the units from Jy to brightness temperature and write the spectrum to a text file. imspec offers Hanning and boxcar spectral smoothing as well as the derivative options available in imspect. You can also specify a cut-off level below which data do not contribute to the spectrum and convert from Jy/beam to Jy.

  Note that the region you specify with imspec is limited to rectangular boxes only. The following example takes a cube in xyv order, computes the spectrum from channels 1 to 256 averaged over the central 4 by 6 arcsec, and then 3-point Hanning smooths it before displaying it on the local X-window.

  IMSPEC
  in=neon.xyv	Input cube
  region=relpix,box(-2,-3,2,3)(1,256)	Region of interest
  plot=average	Plot average
  options=hann,3	Hanning smooth
  cutoff	Unset
  beam	Unset
  axes=ra,dec	Average over RA and DEC axes
  device=/xs	PGPLOT device
  log	Unset