<!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="node693.html"> <LINK REL="previous" HREF="node691.html"> <LINK REL="up" HREF="node689.html"> <LINK REL="next" HREF="node693.html"> </HEAD> <BODY > <!--Navigation Panel--> <A NAME="tex2html10144" HREF="node693.html"> <IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="icons.gif/next_motif.gif"></A> <A NAME="tex2html10141" HREF="node689.html"> <IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="icons.gif/up_motif.gif"></A> <A NAME="tex2html10135" HREF="node691.html"> <IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous" SRC="icons.gif/previous_motif.gif"></A> <A NAME="tex2html10143" 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="tex2html10145" HREF="node693.html">Rebinning</A> <B> Up:</B> <A NAME="tex2html10142" HREF="node689.html">Wavelength calibration</A> <B> Previous:</B> <A NAME="tex2html10136" HREF="node691.html">Offsets between slitlets</A> <BR> <BR> <!--End of Navigation Panel--> <H3><A NAME="SECTION003673300000000000000"> Wavelength calibration</A> </H3> <P> After identifying the arc lines you may now start the actual wavelength calibration with e.g. <P> <BR> <BR> Midas ...> <TT>SET/MOS wlcmet=IC</TT> <P> <BR> <BR> Midas ...> <TT>CALIBRATE/MOS</TT> <P> <BR> <BR> The first character of <!-- MATH: $\fbox{{\small \tt WLCMET}}$ --> <IMG WIDTH="77" HEIGHT="26" ALIGN="BOTTOM" BORDER="0" SRC="img1371.gif" ALT="\fbox{{\small \tt WLCMET}}"> gives the way the first lines are identified (<B>I</B>dentify, <B>L</B>inear, <B>F</B>ors), the second character gives the mode of fitting (<B>C</B>onstant or <B>V</B>ariable linelist, <B>F</B>it all). For a detailed description see subsection <A HREF="node682.html#sec-Man-wlccal">L.3.3</A>. This program fits a dispersion relation at first to the row with the identified lines, then to the slitlet, and afterwards to all slitlets (row by row, separately for each slitlet). The fitted line positions are compared to those listed in <!-- MATH: $\fbox{{\small \tt LINECAT}}$ --> <IMG WIDTH="87" HEIGHT="26" ALIGN="BOTTOM" BORDER="0" SRC="img1372.gif" ALT="\fbox{{\small \tt LINECAT}}">.tbl (<B>hear</B>). The type of polynomials (Legendre or Chebyshev) is read from <!-- MATH: $\fbox{{\small \tt POLTYP}}$ --> <IMG WIDTH="77" HEIGHT="26" ALIGN="BOTTOM" BORDER="0" SRC="img1373.gif" ALT="\fbox{{\small \tt POLTYP}}"> (<B>CHEBYSHEV</B>), the fit order from <!-- MATH: $\fbox{{\small \tt WLCORD(1)}}$ --> <IMG WIDTH="108" HEIGHT="29" ALIGN="BOTTOM" BORDER="0" SRC="img1374.gif" ALT="\fbox{{\small \tt WLCORD(1)}}"> (<B>1</B>), and the tolerance for automatic line identification from <!-- MATH: $\fbox{{\small \tt TOL}}$ --> <IMG WIDTH="45" HEIGHT="26" ALIGN="BOTTOM" BORDER="0" SRC="img1375.gif" ALT="\fbox{{\small \tt TOL}}"> ((<B>2</B>)). <!-- MATH: $\fbox{{\small \tt TOL}}$ --> <IMG WIDTH="45" HEIGHT="26" ALIGN="BOTTOM" BORDER="0" SRC="img1376.gif" ALT="\fbox{{\small \tt TOL}}"> can be given in pixel (> 0) or wavelength units (< 0). In case you know the central wavelength and the mean dispersion of the grism you used and you determined the offsets of the slitlets with <TT>OFFSET/MOS</TT> you have to correct the central wavelength for the offset between the center of the CCD and the reference slitlet used by <TT>OFFSET/MOS</TT>. <DL> <DT><STRONG>Example:</STRONG> <DD>Your reference slitlet has an offset of -100 relative to the center of the CCD in x-direction and you have a mean dispersion of 2Å/pixel and a central wavelength of 5500Å. This central wavelength will always lie at the x-position of the respective slitlet, which is in this case -100pixels (i.e. -200Å) from the center of the CCD. This means that you have a wavelength of 5700Å at the center of the CCD within the reference slitlet. This wavelength should be used as <TT>wcenter</TT>, since the program assumes that <TT>:xoffset = 0</TT> means that the slitlet is at the center of the CCD in x-direction. </DL> <P> Then you can use the following command <P> <BR> <BR> Midas ...> <TT>SET/MOS wcenter=central_wavelength </TT> <P> <BR> <BR> Midas ...> <TT>SET/MOS avdisp=mean_linear_dispersion</TT> <P> <BR> <BR> Midas ...> <TT>SET/MOS wlcmet=LC</TT> <P> <BR> <BR> Midas ...> <TT>CALIBRATE/MOS</TT> <P> <BR> <BR> which will read the two parameters from <!-- MATH: $\fbox{{\small \tt WCENTER}}$ --> <IMG WIDTH="87" HEIGHT="26" ALIGN="BOTTOM" BORDER="0" SRC="img1377.gif" ALT="\fbox{{\small \tt WCENTER}}"> and <!-- MATH: $\fbox{{\small \tt AVDISP}}$ --> <IMG WIDTH="77" HEIGHT="26" ALIGN="BOTTOM" BORDER="0" SRC="img1378.gif" ALT="\fbox{{\small \tt AVDISP}}">. If you have FORS data use <P> <BR> <BR> Midas ...> <TT>SET/MOS wlcmet=RT</TT> <P> <BR> <BR> Midas ...> <TT>CALIBRATE/MOS</TT> <P> <BR> <BR> This will read the grism number from the header of <!-- MATH: $\fbox{{\small \tt WLC}}$ --> <IMG WIDTH="45" HEIGHT="26" ALIGN="BOTTOM" BORDER="0" SRC="img1379.gif" ALT="\fbox{{\small \tt WLC}}"> and then take the parameters stored in the respective keyword. The plot option <!-- MATH: $\fbox{{\small \tt PLOTC}}$ --> <IMG WIDTH="67" HEIGHT="26" ALIGN="BOTTOM" BORDER="0" SRC="img1380.gif" ALT="\fbox{{\small \tt PLOTC}}"> (<B>N</B>) decides whether or not you get a plot of the residuals and the display option <!-- MATH: $\fbox{{\small \tt DISP}}$ --> <IMG WIDTH="56" HEIGHT="26" ALIGN="BOTTOM" BORDER="0" SRC="img1381.gif" ALT="\fbox{{\small \tt DISP}}"> (<B>0</B>) influences the amount of intermediate results displayed on screen. <TT>CALIBRATE/MOS</TT> stores the results in <!-- MATH: $\fbox{{\small \tt LINFIT}}$ --> <IMG WIDTH="77" HEIGHT="26" ALIGN="BOTTOM" BORDER="0" SRC="img1382.gif" ALT="\fbox{{\small \tt LINFIT}}">.tbl (<B>coerbr</B>) in the columns <P><P> <BR> <P> <TABLE CELLPADDING=3 BORDER="1"> <TR><TD ALIGN="LEFT"><TT> :SLIT</TT></TD> <TD ALIGN="LEFT">number of slitlet</TD> </TR> <TR><TD ALIGN="LEFT"><TT> :ROW</TT></TD> <TD ALIGN="LEFT">row for which dispersion relation was fitted (pixel coordinates)</TD> </TR> <TR><TD ALIGN="LEFT"><TT> :Y</TT></TD> <TD ALIGN="LEFT">row for which dispersion relation was fitted (world coordinates)</TD> </TR> <TR><TD ALIGN="LEFT"><TT> :RMS</TT></TD> <TD ALIGN="LEFT">r.m.s. error of fit</TD> </TR> <TR><TD ALIGN="LEFT"><TT> :COEF_i</TT></TD> <TD ALIGN="LEFT">fit coefficients</TD> </TR> </TABLE> <BR> <BR> <BR> <BR> <P> and adds to <!-- MATH: $\fbox{{\small \tt LINPOS}}$ --> <IMG WIDTH="77" HEIGHT="26" ALIGN="BOTTOM" BORDER="0" SRC="img1383.gif" ALT="\fbox{{\small \tt LINPOS}}">.tbl (<B>linpos</B>) the columns <P><P> <BR> <P> <TABLE CELLPADDING=3 BORDER="1"> <TR><TD ALIGN="LEFT"><TT> :WAVE</TT></TD> <TD ALIGN="LEFT">wavelength identification for :X</TD> </TR> <TR><TD ALIGN="LEFT"><TT> :WAVEC</TT></TD> <TD ALIGN="LEFT">fitted wavelength for :X</TD> </TR> <TR><TD ALIGN="LEFT"><TT> :RESIDUAL</TT></TD> <TD ALIGN="LEFT">:WAVE-:WAVEC</TD> </TR> <TR><TD ALIGN="LEFT"><TT> :REJECT</TT></TD> <TD ALIGN="LEFT">mark for rejected lines</TD> </TR> </TABLE> <BR> <P> Slitlets where no dispersion relation could be fitted are marked with '-1' in column <TT>:SLIT</TT>. With <P> <BR> <BR> Midas ...> <TT>RESPLOT/MOS ? slit</TT> <P> <BR> <BR> you can also get a plot of the residuals for a certain slit (<TT>slit</TT> = number) that are stored in <!-- MATH: $\fbox{{\small \tt LINPOS}}$ --> <IMG WIDTH="77" HEIGHT="26" ALIGN="BOTTOM" BORDER="0" SRC="img1384.gif" ALT="\fbox{{\small \tt LINPOS}}">.tbl (<B>linpos</B>) (or in the first parameter given on the command line). <P> <HR> <!--Navigation Panel--> <A NAME="tex2html10144" HREF="node693.html"> <IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="icons.gif/next_motif.gif"></A> <A NAME="tex2html10141" HREF="node689.html"> <IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="icons.gif/up_motif.gif"></A> <A NAME="tex2html10135" HREF="node691.html"> <IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous" SRC="icons.gif/previous_motif.gif"></A> <A NAME="tex2html10143" 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="tex2html10145" HREF="node693.html">Rebinning</A> <B> Up:</B> <A NAME="tex2html10142" HREF="node689.html">Wavelength calibration</A> <B> Previous:</B> <A NAME="tex2html10136" HREF="node691.html">Offsets between slitlets</A> <!--End of Navigation Panel--> <ADDRESS> <I>Petra Nass</I> <BR><I>1999-06-15</I> </ADDRESS> </BODY> </HTML>