<!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>Wavelength calibration</TITLE> <META NAME="description" CONTENT="Wavelength calibration"> <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="node705.html"> <LINK REL="previous" HREF="node703.html"> <LINK REL="up" HREF="node696.html"> <LINK REL="next" HREF="node705.html"> </HEAD> <BODY > <!--Navigation Panel--> <A NAME="tex2html10286" HREF="node705.html"> <IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="icons.gif/next_motif.gif"></A> <A NAME="tex2html10283" HREF="node696.html"> <IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="icons.gif/up_motif.gif"></A> <A NAME="tex2html10277" HREF="node703.html"> <IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous" SRC="icons.gif/previous_motif.gif"></A> <A NAME="tex2html10285" 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="tex2html10287" HREF="node705.html">Rebinning</A> <B> Up:</B> <A NAME="tex2html10284" HREF="node696.html">FEROS</A> <B> Previous:</B> <A NAME="tex2html10278" HREF="node703.html">Flat-fielding</A> <BR> <BR> <!--End of Navigation Panel--> <H1><A NAME="SECTION003780000000000000000"> Wavelength calibration</A> </H1> <P> The wavelength calibration uses the ThArNe calibration frames. The orders are first extracted and then searched for emission lines. This is done with the command SEARCH/FEROS. Wavelengths are assigned to these lines iteratively using a catalog of wavelengths and starting with a preliminary dispersion relation. A global dispersion relation for the whole wavelength rane is used for fitting the line positions as a function of y-position and order number. The global formula used is of the form <P> <BR><P></P> <DIV ALIGN="CENTER"> <!-- MATH: \begin{equation} \lambda m = \sum{\sum{a_{ij} x^i m^j}} \end{equation} --> <TABLE WIDTH="100%" ALIGN="CENTER"> <TR VALIGN="MIDDLE"><TD ALIGN="CENTER" NOWRAP><IMG WIDTH="196" HEIGHT="45" SRC="img1417.gif" ALT="\begin{displaymath}\lambda m = \sum{\sum{a_{ij} x^i m^j}} \end{displaymath}"></TD> <TD WIDTH=10 ALIGN="RIGHT"> (29.1)</TD></TR> </TABLE> </DIV> <BR CLEAR="ALL"><P></P> <P> where <I>x</I> and <I>m</I> are the position along the dispersion axis and the order number, respectively, and <I>a</I><SUB><I>ij</I></SUB> are the coefficients to be fitted. For the order of the polynomial <IMG WIDTH="74" HEIGHT="40" ALIGN="MIDDLE" BORDER="0" SRC="img1418.gif" ALT="$i,j \le 4$"> is sufficient for FEROS. Most of the higher terms are set to zero, so that only 15 free parameters are used. With this formula we can reach residuals of the order of 3mÅ rms over the full wavelength range. The wavelength calibration is done with the command CALIB/FEROS. <P> <BR><HR> <ADDRESS> <I>Petra Nass</I> <BR><I>1999-06-15</I> </ADDRESS> </BODY> </HTML>