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.help sbands Nov93 onedspec
.ih
NAME
sbands -- bandpass spectrophotometry of spectra
.ih
USAGE
sbands input output bands
.ih
PARAMETERS
.ls input
Input list of spectra to be measured. These may be one dimensional
spectra in individual or "multispec" format or calibrated spatial spectra such
as long slit or Fabry-Perot images. The dispersion axis and summing
parameters are specified by package parameters for the spatial spectra.
.le
.ls output
Output file for the results. This may be a filename or "STDOUT" to
write to the terminal.
.le
.ls bands
Bandpass file consisting of lines with one, two, or three bandpasses per
line. A bandpass is specified by an identification string (quoted if it is
null or contains whitespace), the central wavelength, the width of the
bandpass in wavelength, and a filter filename with the special value "none"
if there is no filter (a flat unit response). This format is described
further in the description section.
.le
.ls apertures = ""
List of apertures to select from the input spectra. For one dimensional
spectra this is the aperture number and for spatial spectra it is
the column or line. If the null string is specified all apertures are
selected. The aperture list syntax is a range list which includes
intervals and steps (see \fBranges\fR).
.le
.ls normalize = yes
Normalize the bandpass fluxes by the bandpass response? If no then
the results will depend on the bandpass widths and filter function
values. If yes then fluxes will be comparable to an average pixel
value. When computing indices and equivalent widths the flux must
either be normalized or the bandpasses and filter response functions
must be the same.
.le
.ls mag = no, magzero = 0.
Output the bandpass fluxes as magnitudes with specified magnitude
zero point?
.le
.ls verbose = yes
Include a verbose header giving a banner, the parameters used,
the bandpasses, and column headings?
.le
.ih
DESCRIPTION
\fBSbands\fR performs bandpass spectrophotometry with one or more bandpasses
on one or more spectra. A list of input spectra is specified. The spectra
may be of any type acceptable in the \fBnoao.onedspec\fR package including
multispec format with nonlinear dispersion, long slit spectra, and even
3D cubes with one dispersion axis. The \fIapertures\fR parameter allows
selecting a subset of the spectra by aperture number.
The bandpasses are specified in a text file. A bandpass consists of four
fields; an identification name, the wavelength of the bandpass center, a
bandpass width, and a filename for a filter. The identification is a
string which must be quoted if a null name or a name with whitespace is
desired. The identification could be given as the central wavelength if
nothing else is appropriate. The filter field is a filename for a text
file containing the filter values. A filter file consists of a wavelength
ordered list of wavelength and relative response. Extrapolation uses the
end point values and interpolation is linear. The special name "none" is
used if there is no filter. This is equivalent to unit response at all
wavelengths.
In the bandpass file there may be one, two, or three bandpasses on
a line. Below are some examples of the three cases:
.nf
alpha 5000 10 myalpha.dat
beta1 4000 100 none beta2 4100 100 none
line 4500 100 none red 4000 200 none blue 5000 200 none
.fi
The flux in each bandpass is measured by summing each pixel in the interval
multiplied by the interpolated filter response at that pixel. At the edges
of the bandpass the fraction of the pixel in the bandpass is used. If the
bandpass goes outside the range of the data an INDEF value will be reported.
If the \fInormalize\fR option is yes then the total flux is divided by
the sum of the filter response values. If the \fImag\fR option is
yes the flux will be converted to a magnitude (provided it is positive)
using the formula
.nf
magnitude = magzero - 2.5 * log10 (flux)
.fi
where \fImagzero\fR is a parameter for the zero point magnitude and log10
is the base 10 logarithm. Note that there is no attempt to deal with the
pixel flux units. This is the responsibility of the user.
If there is only one bandpass (on one line of the band file) then only
the band flux or magnitude is reported. If there are two bandpasses
the fluxes or magnitudes for the two bands are reported as well as a
band index, the flux ratio or magnitude difference (depending on the \fImag\fR)
flag, and an equivalent width using the second band as the continuum.
If there are three bandpasses then a continuum bandpass flux is computed
as the interpolation between the bandpass centers to the center of the
first bandpass. The special bandpass identification "cont" will
be reported.
The equivalent width is obtained from the two bandpasses by the
formula
.nf
eq. width = (1 - flux1 / flux2) * width1
.fi
where flux1 and flux2 are the two bandpass fluxes and width1 is the
width of the first bandpass. Note that for this to be meaningful
the bandpasses should be normalized or have the same width/response.
The results of measuring each bandpass in each spectrum are written
to the specified output file. This file may be given as "STDOUT" to
write the results to the terminal. The output file contains lines
with the spectrum name and aperture, the band identifications and
fluxes or magnitudes, and the band index and equivalent width (if
appropriate). The \fIverbose\fR option allows creating a more
documented output by including a commented header with the task
name and parameters, the bandpass definitions, and column labels.
The examples below show the form of the output.
.ih
EXAMPLES
The following examples use artificial data and arbitrary bands.
1. Show example results with one, two, and three bandpass entries in
the bandpass file.
.nf
cl> type bands
test 6125 50 none red 6025 100 none blue 6225 100 none
test 6125 50 none red 6025 100 none
test 6125 50 none blue 6225 100 none
test 6125 50 none
cl> sbands oned STDOUT bands
# SBANDS: NOAO/IRAF IRAFX valdes@puppis Mon 15:31:45 01-Nov-93
# bands = bands, norm = yes, mag = no
# band filter wavelength width
# test none 6125. 50.
# red none 6025. 100.
# blue none 6225. 100.
# test none 6125. 50.
# red none 6025. 100.
# test none 6125. 50.
# blue none 6225. 100.
# test none 6125. 50.
#
# spectrum band flux band flux index eqwidth
oned(1) test 44.33 cont 97.97 0.45 27.37
oned(1) test 44.33 red 95.89 0.46 26.89
oned(1) test 44.33 blue 100.04 0.44 27.84
oned(1) test 44.33
.fi
2. This example shows measurements on a long slit spectrum with an
aperture selection and magnitude output.
.nf
cl> type lsbands.dat
band1 4500 40 none
band2 4600 40 none
band3 4700 40 none
cl> nsum=5
cl> sbands ls STDOUT lsbands.dat apertures=40-60x5 mag+ magzero=10.1
# SBANDS: NOAO/IRAF IRAFX valdes@puppis Mon 15:37:18 01-Nov-93
# bands = lsbands.dat, norm = yes, mag = yes, magzero = 10.10
# band filter wavelength width
# band1 none 4500. 40.
# band2 none 4600. 40.
# band3 none 4700. 40.
#
# spectrum band mag
ls[38:42,*](40) band1 3.14
ls[38:42,*](40) band2 3.19
ls[38:42,*](40) band3 3.15
ls[43:47,*](45) band1 3.13
ls[43:47,*](45) band2 3.15
ls[43:47,*](45) band3 3.14
ls[48:52,*](50) band1 2.34
ls[48:52,*](50) band2 2.43
ls[48:52,*](50) band3 2.43
ls[53:57,*](55) band1 3.10
ls[53:57,*](55) band2 3.15
ls[53:57,*](55) band3 3.12
ls[58:62,*](60) band1 3.14
ls[58:62,*](60) band2 3.19
ls[58:62,*](60) band3 3.15
.fi
.ih
REVISIONS
.ls SBANDS V2.10.4
The flux column is now printed to 6 digits of precision with possible
exponential format to permit flux calibrated spectra to print properly.
.le
.ls SBANDS V2.10.3
The task is new in this release
.le
.ih
SEE ALSO
splot
.endhelp
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