sumspec Example 1

Galaxy Emission Template at Zero Redshift


Create a zero-velocity template spectrum by combining several spectra of galaxies with prominent emission lines for use by the IRAF xcsao cross-correlation task.


Three spectra from SAO's FAST long-slit spectrograph with prominent emission lines, but different redshifts were selected for combination. The file names were placed in the file emcomp.list:

Relative Velocities

Redshifts were obtained for the spectra using the emsao task of the rvsao IRAF package using these parameters. Note that save_vel is set to yes so that the velocity and barycentric velocity correction will be stored in the header as VELOCITY and BCV.

Combining the Spectra

The program is run using the command
  rv> sumspec @emcomp.list emcomp
As the wavelength limits st_lambda and end_lambda are both set to INDEF, the wavelength coverage of each spectrum is computed red- or blue-shifted from the header VELOCITY to the desired output radial velocity, velcomp, and the region of overlap is used. Each spectrum is read, shifted from the header VELOCITY to velcomp, and rebinned to be linear in log-wavelength. A continuum is fit and subtracted, and the spectra are added one at a time to make the resulting composite spectrum.


As each spectrum is added, a summary is written to the device(s) specified by the logfiles parameter:
IRAF rvsao.sumspec 2.0b mink@xena Fri 11:19:02 02-May-97
ADDSPEC: Object at 13:26:29.49  0:12:51.69 1950.000
ADDSPEC  02-May-1997 11:20 making emcomp
ADDSPEC: added, shifted 6446.84 - 4.07
ADDSPEC: added, shifted 14385.28 - 25.30
ADDSPEC: added, shifted 11585.76 - -28.74
The velocity and information about the spectra which were used are added to the header of the output spectrum:
 HISTORY   SUMSPEC  02-May-1997 11:20 add FAST
 HISTORY   6446.84 - 4.07
 HISTORY   SUMSPEC  02-May-1997 11:22 add FAST
 HISTORY   14385.28 - 25.30
 HISTORY   SUMSPEC  02-May-1997 11:23 add FAST
 HISTORY   11585.76 - -28.74
An emission line velocity can be found using emsao. A cross-correlation velocity can be found using xcsao.

Last updated May 6, 1997 by Doug Mink

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