<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN"> <!--Converted with LaTeX2HTML 98.1p1 release (March 2nd, 1998) originally by Nikos Drakos (nikos@cbl.leeds.ac.uk), CBLU, University of Leeds * revised and updated by: Marcus Hennecke, Ross Moore, Herb Swan * with significant contributions from: Jens Lippmann, Marek Rouchal, Martin Wilck and others --> <HTML> <HEAD> <TITLE>Offsets between slitlets</TITLE> <META NAME="description" CONTENT="Offsets between slitlets"> <META NAME="keywords" CONTENT="vol2"> <META NAME="resource-type" CONTENT="document"> <META NAME="distribution" CONTENT="global"> <META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1"> <LINK REL="STYLESHEET" HREF="vol2.css"> <LINK REL="next" HREF="node682.html"> <LINK REL="previous" HREF="node680.html"> <LINK REL="up" HREF="node679.html"> <LINK REL="next" HREF="node682.html"> </HEAD> <BODY > <!--Navigation Panel--> <A NAME="tex2html10014" HREF="node682.html"> <IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="icons.gif/next_motif.gif"></A> <A NAME="tex2html10011" HREF="node679.html"> <IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="icons.gif/up_motif.gif"></A> <A NAME="tex2html10005" HREF="node680.html"> <IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous" SRC="icons.gif/previous_motif.gif"></A> <A NAME="tex2html10013" HREF="node1.html"> <IMG WIDTH="65" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="contents" SRC="icons.gif/contents_motif.gif"></A> <BR> <B> Next:</B> <A NAME="tex2html10015" HREF="node682.html">Fitting the dispersion curve</A> <B> Up:</B> <A NAME="tex2html10012" HREF="node679.html">Wavelength Calibration</A> <B> Previous:</B> <A NAME="tex2html10006" HREF="node680.html">Detection of Arc lines</A> <BR> <BR> <!--End of Navigation Panel--> <H2><A NAME="SECTION003632000000000000000"> Offsets between slitlets</A> </H2> <P> If you have used <TT>DEFINE/SLIT</TT> there are no offsets copied to <!-- MATH: $\fbox{{\small \tt MOS}}$ --> <IMG WIDTH="45" HEIGHT="26" ALIGN="BOTTOM" BORDER="0" SRC="img1193.gif" ALT="\fbox{{\small \tt MOS}}">.tbl automatically and you have to determine the offsets yourself using the command <TT>OFFSET/MOS</TT> on a wavelength calibration frame. This command will take the calibration spectra of the different slitlets and search for arc lines with the parameters given by <!-- MATH: $\fbox{{\small \tt SEAPAR}}$ --> <IMG WIDTH="77" HEIGHT="26" ALIGN="BOTTOM" BORDER="0" SRC="img1194.gif" ALT="\fbox{{\small \tt SEAPAR}}"> (<B>200,5</B>). Correlating these line lists with that of the first slitlet gives the offsets relative to the first slitlet. The resulting offsets may be wrong if there are not enough or too many lines to get unambiguous correlation results. The safest way is to use this command after you are satisfied with the results of <TT>SEARCH/MOS</TT> <B>and</B> you have stored the parameters for threshold and width to <!-- MATH: $\fbox{{\small \tt SEAPAR}}$ --> <IMG WIDTH="77" HEIGHT="26" ALIGN="BOTTOM" BORDER="0" SRC="img1195.gif" ALT="\fbox{{\small \tt SEAPAR}}">. In this case you will <B>NOT</B> have <B>the offsets from the center of the CCD but relative to the position of the first slitlet!</B> The changing image scale over the detector can make the method unappropiate. Therefore it is strongly recommended to copy the offsets from descriptor data to the <!-- MATH: $\fbox{{\small \tt MOS}}$ --> <IMG WIDTH="45" HEIGHT="26" ALIGN="BOTTOM" BORDER="0" SRC="img1196.gif" ALT="\fbox{{\small \tt MOS}}">.tbl table, but not from <TT>OFFSET/MOS</TT> - if possible. <P> <BLOCKQUOTE> <DIV ALIGN="CENTER"> <B>Note</DIV> <I>Before starting the calibration, a carefully selected line catalog must be prepared. Reject any line that is below the detection limit and any line which is blended!</I></B></BLOCKQUOTE><HR> <!--Navigation Panel--> <A NAME="tex2html10014" HREF="node682.html"> <IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="icons.gif/next_motif.gif"></A> <A NAME="tex2html10011" HREF="node679.html"> <IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="icons.gif/up_motif.gif"></A> <A NAME="tex2html10005" HREF="node680.html"> <IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous" SRC="icons.gif/previous_motif.gif"></A> <A NAME="tex2html10013" HREF="node1.html"> <IMG WIDTH="65" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="contents" SRC="icons.gif/contents_motif.gif"></A> <BR> <B> Next:</B> <A NAME="tex2html10015" HREF="node682.html">Fitting the dispersion curve</A> <B> Up:</B> <A NAME="tex2html10012" HREF="node679.html">Wavelength Calibration</A> <B> Previous:</B> <A NAME="tex2html10006" HREF="node680.html">Detection of Arc lines</A> <!--End of Navigation Panel--> <ADDRESS> <I>Petra Nass</I> <BR><I>1999-06-15</I> </ADDRESS> </BODY> </HTML>