Galaxy Emission Template at Zero Redshift
Problem
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.
Setup
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:
1995.0402.0118.13265p0012.ms
1995.1122.0113.311.062165.ms
1996.0123.0052.465.011857.ms
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.
Results
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: 1995.0402.0118.13265p0012.ms added, shifted 6446.84 - 4.07
ADDSPEC: 1995.1122.0113.311.062165.ms added, shifted 14385.28 - 25.30
ADDSPEC: 1996.0123.0052.465.011857.ms 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 1995.0402.0118.13265p0012.ms
HISTORY 6446.84 - 4.07
HISTORY SUMSPEC 02-May-1997 11:22 add FAST 1995.1122.0113.311.062165.ms
HISTORY 14385.28 - 25.30
HISTORY SUMSPEC 02-May-1997 11:23 add FAST 1996.0123.0052.465.011857.ms
HISTORY 11585.76 - -28.74
An emission line velocity can be found using
emsao.
A cross-correlation velocity can be found using
xcsao.
[rvsao]
[sumspec]
[sumspec examples]