.help extras Sep95 noao.twodspec.apextract
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NAME
extras -- Information about the extra bands in 3D output
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DESCRIPTION
When one dimensional spectra are extracted by the tasks in the
\fBapextract\fR package the user may specify that additional
extra associated information be extracted at the same time.  This
information is produced when the \fIextras\fR parameter is "yes".

The associated information is recorded as additional "bands" (the IRAF term
for the third dimension of a three dimensional image) of the output
extracted spectral image.  Extracted spectra are currently stored as IRAF
images with dispersion information given in the image header.  The
image axes for such images are:

.nf
    1 (columns) - dispersion axis
    2 (lines)   - spectrum axis (each line is a separate spectrum)
    3 (bands)   - extras axis (each band is associated data)
.fi

The lengths of the second and third axes, that is the number of
lines and bands, may be one or more.  If there is only one band
the image will be two dimensional and if there is only one line
and one band the image will be one dimensional.  Note that the
\fIformat\fR parameter controls whether multiple apertures are
written to separate images or to a single image.  Thus, if
the format is "onedspec" this means that the second dimension
will always be of length one and, if the \fIextras\fR parameter
is no, the output images will be one dimensional.

The associated data in the image bands depends on which extraction
options are performed.  The various types of data are:

.nf
    The primary spectrum flux values.
    Simple aperture sum if variance weighting or cleaning was done.
    Background spectrum if background subtraction was done.
    Sigma spectrum if variance weighting or cleaning was done.
.fi

The primary spectrum is always the first band and will be the cleaned
and/or variance weighted and/or background subtracted spectrum.  The
simple aperture sum spectrum allows comparing against the results of the
variance weighting or pixel rejection options.  When background
subtraction is performed the subtracted background is recorded in
one of the bands.  When variance weighting or pixel rejection is
performed the software generates an estimate of the uncertainty
in the extracted flux as a sigma.

The identity of the various bands is given by the image header
keywords BANDIDn (where n is the band number).  This also serves
to document which extraction options were used.

For more information get help under the topic "apextract.package".
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SEE ALSO
apextract.package
.endhelp
