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diff --git a/noao/imred/echelle/doc/Tutorial.hlp b/noao/imred/echelle/doc/Tutorial.hlp new file mode 100644 index 00000000..655ca307 --- /dev/null +++ b/noao/imred/echelle/doc/Tutorial.hlp @@ -0,0 +1,184 @@ +.help Tutorial Aug86 "Echelle Tutorial" +.ih +TOPICS +The echelle tutorial consists of a number of different topics. To obtain help +on a particular topic type "tutor topic" where the topic is one of the +following: + +.nf + TOPICS + + topics - List of topics + overview - An overview of the echelle reduction process + dataio - Reading and writing data tapes + tracing - Tracing the positions of the orders + extraction - Extracting one or two dimensional spectra + references - Additional references + all - Print all of the tutorial +.fi + +The topics are kept brief and describe the simplest operations. More +sophisticated discussions are available for all the tasks in the printed +documentation and through the on-line \fBhelp\fR facility; i.e. "help taskname". +.ih +OVERVIEW +The \fBechelle\fR package provides for the extraction of the orders from +two dimensional echelle images into one dimensional spectra. After extraction +the one dimensional spectra are wavelength and flux calibrated. The usual +flow of the reductions is +.ls (1) +Read data from tape. +.le +.ls (2) +Set the dispersion axis in the image headers using the task \fBsetdisp\fR. +This is required by many of the tasks which follow. +.le +.ls (3) +Trace one or more images to define the positions of the orders within the +two dimensional format. +.le +.ls (4) +Extract the orders into one dimensional spectra. +.le +.ls (5) +Use arc calibration spectra to determine wavelength solutions. +.le +.ls (6) +Apply the wavelength solutions to the other spectra and rebin the spectra +into linear or logarithmic wavelength intervals. +.le +.ls (7) +Determine flux calibrations using standard star observations. +.le +.ls (8) +Apply the flux calibrations to the other object spectra. +.le +.ls (9) +Save the reductions as FITS images and make plots of the spectra. +.le + +There are many variations on these steps possible with the great flexibility +of the reduction tools at your disposal. The most important one to mention +is that the orders may be extracted as two dimensional strips in order to +apply more complex geometric distortion corrections using the \fBlongslit\fR +package. +.ih +DATAIO +To read CCD Camera format tapes use \fBrcamera\fR from the \fBmtlocal\fR +package. FITS format tapes are read and written with \fBrfits\fR and +\fBwfits\fR from the \fBdataio\fR package. Remember you need to +\fBallocate\fR the tape drive before you can read or write tapes and +you should \fBdeallocate\fR the tapes when you are through with the +tape drive. + +.nf + ec> allocate mta + ec> deallocate mta + ec> rcamera mta 1-99 ech datatype=r >rcam.log & + ec> rfits mta 1-99 ech datatype=r >rfits.log & + ec> wfits mta spectra* +.fi +.ih +TRACING +The positions of the orders across the image dispersion axis as a function +of position along the dispersion axis are determined by the task \fBtrace\fR. +There are three steps in tracing an image; defining the initial positions of +the orders at one point along the dispersion, automatically determining +the positions at other points in steps from the starting point, and fitting +smooth curves to the positions as a function of dispersion position. The +first and last steps are interactive, at least initially. After the first +image other images may be traced noninteractively. + +Select an image with narrow, strong profiles and run trace: + + ec> trace imagename + +When you are asked if you want to edit the apertures respond with "yes". +The central cut across the dispersion is graphed. Position the cursor +over the first order to be traced and type 'm'. Adjust the width of the +extraction aperture with the 'l', 'u', or 'y' keys or specify the lower +and upper widths explicitly with ":lower value" or ":upper value". +If background subtraction is to be used type 'b' and set the background +fitting parameters (see the \fBbackground\fR tutorial) +Now mark the remaining orders with the 'm' key. The widths of the +previous aperture are preserved for each new aperture. When you are +satisfied with the marked apertures type 'q'. + +The positions of the orders are now traced in steps from the initial point. +Once the positions have been traced you are asked whether to fit the +traced apertures interactively. Respond with "yes". You will now be +asked specifically if the first aperture is to be fit. Respond with "yes" +again. The traced positions are graphed along with a fitted curve. You now +have many options for adjusting the fit. The most important one is the +order which is set by typing ":order value", where value is the desired +order, and then 'f' to refit the data. For full information of the +options see the help for \fBicfit\fR. When you are satisfied type 'q'. + +You are then prompted for the next order. The previous fitting parameters +will be used so at this point you may want to just answer "NO" to skip +the interactive fitting of the other traced orders, though the graphs of the +fit will still be displayed. + +You now have several options about how to define the positions of the +orders in your other images. + +.ls (1) +You may apply the tracing to all other observations with no +further tracing. This is done by specifying the traced image +as the "reference" in the extraction process. +.le +.ls (2) +You may maintain the same shape of the traces and correct for +shifts in the positions of the orders across the dispersion +by recentering each aperture. This is done +with the task \fBapedit\fR or the editing switch during extraction +using the first traced image as the reference. The apertures are +recenter using the 'c' key. +.le +.ls (3) +Finally, you may retrace other images either from scratch or +using the first traced image as the initial reference. In the latter +case the tracing may be done noninteractively as a batch process. +.le +.ih +EXTRACTION +There are two types of extraction; to one dimensional spectra or +to two dimensional strips. The second type of extraction is accomplished +by the task \fBstripextract\fR in the \fBtwodspec.apextract\fR package +and is used if further reductions using the \fBlongslit\fR package are +desired. Normally, however, one ignores the small geometric distortion +in which curves of constant wavelength differ slightly from the image +dispersion axis. + +Extraction of the traced echelle orders is performed by the task +\fBsumextract\fR. The pixels within each aperture at each point along +the dispersion axis are summed to produce one dimensional spectra, one +for each order and each extracted image. The sum may be weighted +in two ways; "profile" or "variance" weighting. The variance weighting +may require that you know the CCD readout noise and photon/ADU conversion. +For a description of the weights see the help for \fBsumextract\fR +or the paper "The APEXTRACT Package". The spectra may also be cleaned +of cosmic rays and bad pixels at the same time and have a background +subtracted. The background subtraction parameters must be set when +defining the apertures or later using the apedit mode in \fBapedit\fR, +\fBtrace\fR, or \fBsumextract\fR. See the tutorial on \fBbackground\fR +for further information. + +Once the extraction parameters have been set simply type + + ec> sumextract images + +where images is the list of images to be extracted. If each image has +not been traced then a traced reference image should be given. +One may correct for shifts relative to the traced image by setting the +switch to edit the apertures and then recentering each aperture before +extracting. If there is no aperture editing then the extractions may +be done as a background or batch process. +.ih +REFERENCES +.ls (1) +Pilachowski, C. and J. V. Barnes, \fINotes on the IRAF for Reduction of +Echelle/CCD Data\fR, NOAO Central Computer Services, 1986. This document +is also available in the \fBIRAF User Handbook , Vol. 2B -- NOAO Cookbooks\fR. +.le +.endhelp |