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<H2><A NAME="SECTION003675000000000000000">
Object extraction</A>
</H2>
<P>
Use <TT>EXTRACT/MOS</TT> to sky-subtract and extract the detected objects in
an output frame
with an optimum extraction
scheme using different weights for the individual rows (following Horne, 1986,
PASP 98, 609).
The procedure is iterative. If the number of iterations
<!-- MATH: $\fbox{{\small \tt EXTPAR(2)}}$ -->
<IMG
WIDTH="108" HEIGHT="29" ALIGN="BOTTOM" BORDER="0"
SRC="img1406.gif"
ALT="\fbox{{\small \tt EXTPAR(2)}}">is set to a negative number, a spectrum computed with equal weights
is returned. The sky frame (
<!-- MATH: $\fbox{{\small \tt SKYFRAME}}$ -->
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(<B>sky</B>)) and the CCD
read-out-noise and gain (
<!-- MATH: $\fbox{{\small \tt CCDPAR}}$ -->
<IMG
WIDTH="77" HEIGHT="26" ALIGN="BOTTOM" BORDER="0"
SRC="img1408.gif"
ALT="\fbox{{\small \tt CCDPAR}}">)
are used to compute the errors
of the resulting spectra.
The extracted spectra are stored in a 2-D frame, each line
corresponding to one extracted object. In addition, the errors for the
extracted spectra are stored in this frame, one line per spectrum.
<P>
To rebin the resulting frames to constant wavelength steps use:
<P>
<BR>
<BR>
Midas
...> <TT>SET/MOS extobjec=in</TT>
<P>
<BR>
<BR>
Midas ...> <TT>SET/MOS rebstrt=start rebend=end rebstp=step</TT>
<P>
<BR>
<BR>
Midas ...> <TT>REB1D/MOS ? reb</TT>
<P>
<BR>
<BR>
This will split the extracted frame in.bdf into individual frames with
constant wavelength steps, named reb0001, reb0002, etc.
using the dispersion coefficients of
<!-- MATH: $\fbox{{\small \tt LINFIT}}$ -->
<IMG
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ALT="\fbox{{\small \tt LINFIT}}">.tbl.
<P>
If you want to avoid rebinning noise you can use <TT>APPLY/MOS</TT> to produce
a table with the columns <TT>:WAVELENGTH, :FLUX, :FLUX_ERROR,</TT>
and <TT>:BIN</TT>.
<P>
<BR>
<BR>
Midas
...> <TT>SET/MOS extobjec=in calobjec=ap</TT>
<P>
<BR>
<BR>
Midas ...> <TT>APPLY/MOS</TT>
<P>
<BR>
<BR>
This will take the frame in.bdf and convert it to tables ap0001.tbl,
ap0002.tbl,
etc. using the dispersion coefficients of
<!-- MATH: $\fbox{{\small \tt LINFIT}}$ -->
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WIDTH="77" HEIGHT="26" ALIGN="BOTTOM" BORDER="0"
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<P>
=31 =03 =1999
<P>
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<ADDRESS>
<I>Petra Nass</I>
<BR><I>1999-06-15</I>
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