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+.help doecslit Feb93 noao.imred.echelle
+.ih
+NAME
+doecslit -- Echelle slit spectra reduction task
+.ih
+USAGE
+doecslit objects
+.ih
+SUMMARY
+\fBDoecslit\fR subtracts background sky or scattered light, extracts,
+wavelength calibrates, and flux calibrates multiorder echelle slit spectra
+which have been processed to remove the detector characteristics; i.e. CCD
+images have been bias, dark count, and flat field corrected.  The spectra
+should be oriented such that pixels of constant wavelength are aligned with
+the image columns or lines.  Small departures from this alignment are not
+critical resulting in only a small loss of resolution.  Single order
+observations should be reduced with \fBdoslit\fR.
+.ih
+PARAMETERS
+.ls objects
+List of object images to be processed.  Previously processed spectra are
+ignored unless the \fIredo\fR flag is set or the \fIupdate\fR flag is set
+and dependent calibration data has changed.  If the images contain the
+keyword IMAGETYP then only those with a value of "object" or "OBJECT"
+are used and those with a value of "comp" or "COMPARISON" are added
+to the list of arcs.  Extracted spectra are ignored.
+.le
+.ls apref = ""
+Aperture reference spectrum.  This spectrum is used to define the basic
+extraction apertures and is typically a bright star spectrum.
+.le
+.ls arcs = "" (at least one if dispersion correcting)
+List of arc calibration spectra.  These spectra are used to define
+the dispersion functions.  The first spectrum is used to mark lines
+and set the dispersion function interactively and dispersion functions
+for all other arc spectra are derived from it.  If the images contain
+the keyword IMAGETYP then only those with a value of "comp" or
+"COMPARISON" are used.  All others are ignored as are extracted spectra.
+.le
+.ls arctable = "" (optional) (refspectra)
+Table defining which arc spectra are to be assigned to which object
+spectra (see \fBrefspectra\fR).  If not specified an assignment based
+on a header parameter, \fIsparams.sort\fR, such as the Julian date
+is made.
+.le
+.ls standards = "" (at least one if flux calibrating)
+List of standard star spectra.  The standard stars must have entries in
+the calibration database (package parameter \fIechelle.caldir\fR).
+.le
+
+.ls readnoise = 0., gain = 1. (apsum)
+Read out noise in photons and detector gain in photons per data value.
+This parameter defines the minimum noise sigma and the conversion between
+photon Poisson statistics and the data number statistics.  Image header
+keywords (case insensitive) may be specified to obtain the values from the
+image header.
+.le
+.ls datamax = INDEF (apsum.saturation)
+The maximum data value which is not a cosmic ray.
+When cleaning cosmic rays and/or using variance weighted extraction
+very strong cosmic rays (pixel values much larger than the data) can
+cause these operations to behave poorly.  If a value other than INDEF
+is specified then all data pixels in excess of this value will be
+excluded and the algorithms will yield improved results.
+This applies only to the object spectra and not the standard star or
+arc spectra.  For more
+on this see the discussion of the saturation parameter in the
+\fBapextract\fR package.
+.le
+.ls norders = 10 (apfind)
+Number of orders to be found automatically.
+.le
+.ls width = 5. (apedit)
+Approximate full width of the spectrum profiles.  This parameter is used
+to define a width and error radius for the profile centering algorithm,
+and defaults for the aperture limits and background regions.
+.le
+
+.ls dispcor = yes
+Dispersion correct spectra?  This may involve either defining a nonlinear
+dispersion coordinate system in the image header or resampling the
+spectra to uniform linear wavelength coordinates as selected by
+the parameter \fIsparams.linearize\fR.
+.le
+.ls extcor = no
+Extinction correct the spectra?
+.le
+.ls fluxcal = no
+Flux calibrate the spectra using standard star observations?
+.le
+.ls resize = no (apresize)
+Resize the defaults apertures for each object based on the spectrum profile?
+.le
+.ls clean = no (apsum)
+Detect and correct for bad pixels during extraction?  This is the same
+as the clean option in the \fBapextract\fR package.  If yes this also
+implies variance weighted extraction.  In addition the datamax parameters
+can be useful.
+.le
+.ls trace = yes (non-quicklook mode only) (aptrace)
+Allow tracing each object spectrum separately?  If not set then the trace
+from the aperture reference is used, with recentering to allow for shifts
+across the dispersion.  If set then each object and standard star
+image is retraced.  Retracing is NOT done in quicklook mode.
+.le
+.ls background = "none" (apsum, apscatter)
+Type of background light subtraction.  The choices are "none" for no
+background subtraction, "scattered" for a global scattered light
+subtraction, "average" to average the background within background regions,
+"median" to use the median in background regions, "minimum" to use the
+minimum in background regions, or "fit" to fit across the dispersion using
+the background within background regions.  The scattered light option fits
+and subtracts a smooth global background and modifies the input images.
+This is a slow operation and so is NOT performed in quicklook mode.  The
+other background options are local to each aperture.  The "fit" option uses
+additional fitting parameters from \fBsparams\fR and the "scattered" option
+uses parameters from \fBapscat1\fR and \fBapscat2\fR.
+.le
+.ls splot = no
+Plot the final spectra?  In quicklook mode a noninteractive, stacked plot
+is automatically produced using the task \fBspecplot\fR while in
+non-quicklook mode a query is given and the task \fBsplot\fR is used for
+interactive plotting.
+.le
+.ls redo = no
+Redo operations previously done?  If no then previously processed spectra
+in the objects list will not be processed unless required by the
+update option.
+.le
+.ls update = no
+Update processing of previously processed spectra if the aperture
+reference image, the dispersion reference image, or standard star
+calibration data are changed?
+.le
+.ls quicklook = no
+Extract and calibrate spectra with minimal interaction?  In quicklook mode
+only aperture reference definitions, the initial dispersion function
+solution, and the standard star setup are done interactively.  Scattered
+light subtraction and individual object tracing are not performed.
+Normally the \fIsplot\fR option is set in this mode to produce an automatic
+final spectrum plot for each object.  It is recommended that this mode not be
+used for final reductions.
+.le
+.ls batch = no
+Process spectra as a background or batch job provided there are no interactive
+steps remaining.
+.le
+.ls listonly = no
+List processing steps but don't process?
+.le
+
+.ls sparams = "" (pset)
+Name of parameter set containing additional processing parameters.  This
+parameter is only for indicating the link to the parameter set
+\fBsparams\fR and should not be given a value.  The parameter set may be
+examined and modified in the usual ways (typically with "epar
+sparams" or ":e sparams" from the parameter editor).  The parameters are
+described below.
+.le
+
+.ce
+-- GENERAL PARAMETERS --
+.ls line = INDEF, nsum = 10
+The dispersion line (line or column perpendicular to the dispersion
+axis) and number of adjacent lines (half before and half after unless
+at the end of the image) used in finding, recentering, resizing,
+editing, and tracing operations.  A line of INDEF selects the middle of the
+image along the dispersion axis.
+.le
+.ls extras = no (apsum)
+Include raw unweighted and uncleaned spectra, the background spectra, and
+the estimated sigma spectra in a three dimensional output image format.
+See the discussion in the \fBapextract\fR package for further information.
+.le
+
+.ce
+-- AUTOMATIC APERTURE RESIZING PARAMETERS --
+.ls ylevel = 0.05 (apresize)
+Fraction of the peak to set aperture limits during automatic resizing.
+.le
+
+.ce
+-- TRACE PARAMETERS --
+.ls t_step = 10 (aptrace)
+Step along the dispersion axis between determination of the spectrum
+positions.  Note the \fInsum\fR parameter is also used to enhance the
+signal-to-noise at each step.
+.le
+.ls t_function = "spline3", t_order = 2 (aptrace)
+Default trace fitting function and order.  The fitting function types are
+"chebyshev" polynomial, "legendre" polynomial, "spline1" linear spline, and
+"spline3" cubic spline.  The order refers to the number of
+terms in the polynomial functions or the number of spline pieces in the spline
+functions.
+.le
+.ls t_niterate = 1, t_low = 3., t_high = 3. (aptrace)
+Default number of rejection iterations and rejection sigma thresholds.
+.le
+
+.ce
+-- BACKGROUND AND SCATTERED LIGHT PARAMETERS --
+.ls b_function = "legendre", b_order = 1 (apsum)
+Default background fitting function and order.  The fitting function types are
+"chebyshev" polynomial, "legendre" polynomial, "spline1" linear spline, and
+"spline3" cubic spline.  The order refers to the number of
+terms in the polynomial functions or the number of spline pieces in the spline
+functions.
+.le
+.ls b_naverage = -100 (apsum)
+Default number of points to average or median.  Positive numbers
+average that number of sequential points to form a fitting point.
+Negative numbers median that number, in absolute value, of sequential
+points.  A value of 1 does no averaging and each data point is used in the
+fit.
+.le
+.ls b_niterate = 0 (apsum)
+Default number of rejection iterations.  If greater than zero the fit is
+used to detect deviant fitting points and reject them before repeating the
+fit.  The number of iterations of this process is given by this parameter.
+.le
+.ls b_low_reject = 3., b_high_reject = 3. (apsum)
+Default background lower and upper rejection sigmas.  If greater than zero
+points deviating from the fit below and above the fit by more than this
+number of times the sigma of the residuals are rejected before refitting.
+.le
+.ls buffer = 1. (apscatter)
+Buffer distance from the edge of any aperture for data to be included
+in the scattered light determination.  This parameter may be modified
+interactively.
+.le
+.ls apscat1 = "", apscat2 = "" (apscatter)
+Parameter sets for the fitting functions across and along the dispersion.
+These parameters are those used by \fBicfit\fR.  These parameters are
+usually set interactively.
+.le
+
+.ce
+-- APERTURE EXTRACTION PARAMETERS --
+.ls weights = "none" (apsum) (none|variance)
+Type of extraction weighting.  Note that if the \fIclean\fR parameter is
+set then the weights used are "variance" regardless of the weights
+specified by this parameter.  The choices are:
+.ls "none"
+The pixels are summed without weights except for partial pixels at the
+ends.
+.le
+.ls "variance"
+The extraction is weighted by the variance based on the data values
+and a poisson/ccd model using the \fIgain\fR and \fIreadnoise\fR
+parameters.
+.le
+.le
+.ls pfit = "fit1d" (apsum and approfile) (fit1d|fit2d)
+Type of profile fitting algorithm to use.  The "fit1d" algorithm is
+preferred except in cases of extreme tilt.
+.le
+.ls lsigma = 3., usigma = 3. (apsum)
+Lower and upper rejection thresholds, given as a number of times the
+estimated sigma of a pixel, for cleaning.
+.le
+
+.ce
+-- ARC DISPERSION FUNCTION PARAMETERS --
+.ls threshold = 10. (identify/reidentify)
+In order for a feature center to be determined the range of pixel intensities
+around the feature must exceed this threshold.
+.le
+.ls coordlist = "linelist$thar.dat" (ecidentify)
+Arc line list consisting of an ordered list of wavelengths.
+Some standard line lists are available in the directory "linelist$".
+.le
+.ls match = 1. (ecidentify)
+The maximum difference for a match between the dispersion function computed
+value and a wavelength in the coordinate list.
+.le
+.ls fwidth = 4. (ecidentify)
+Approximate full base width (in pixels) of arc lines.
+.le
+.ls cradius = 10. (reidentify)
+Radius from previous position to reidentify arc line.
+.le
+.ls i_function = "legendre", i_xorder = 3, i_yorder = 3 (ecidentify)
+The default function, function order for the pixel position dependence, and
+function order for the aperture number dependence to be fit to the arc
+wavelengths.  The functions choices are "chebyshev" or "legendre".
+.le
+.ls i_niterate = 3, i_low = 3.0, i_high = 3.0 (ecidentify)
+Number of rejection iterations and sigma thresholds for rejecting arc
+lines from the dispersion function fits.
+.le
+.ls refit = yes (ecreidentify)
+Refit the dispersion function?  If yes and there is more than 1 line
+and a dispersion function was defined in the arc reference then a new
+dispersion function of the same type as in the reference image is fit
+using the new pixel positions.  Otherwise only a zero point shift is
+determined for the revised fitted coordinates without changing the
+form of the dispersion function.
+.le
+
+.ce
+-- AUTOMATIC ARC ASSIGNMENT PARAMETERS --
+.ls select = "interp" (refspectra)
+Selection method for assigning wavelength calibration spectra.
+Note that an arc assignment table may be used to override the selection
+method and explicitly assign arc spectra to object spectra.
+The automatic selection methods are:
+.ls average
+Average two reference spectra without regard to any sort parameter.
+If only one reference spectrum is specified then it is assigned with a
+warning.  If more than two reference spectra are specified then only the
+first two are used and a warning is given.
+This option is used to assign two reference spectra, with equal weights,
+independent of any sorting parameter.
+.le
+.ls following
+Select the nearest following spectrum in the reference list based on the
+sorting parameter.  If there is no following spectrum use the nearest preceding
+spectrum.
+.le
+.ls interp
+Interpolate between the preceding and following spectra in the reference
+list based on the sorting parameter.  If there is no preceding and following
+spectrum use the nearest spectrum.  The interpolation is weighted by the
+relative distances of the sorting parameter.
+.le
+.ls match
+Match each input spectrum with the reference spectrum list in order.
+This overrides the reference aperture check.
+.le
+.ls nearest
+Select the nearest spectrum in the reference list based on the sorting
+parameter.
+.le
+.ls preceding
+Select the nearest preceding spectrum in the reference list based on the
+sorting parameter.  If there is no preceding spectrum use the nearest following
+spectrum.
+.le
+.le
+.ls sort = "jd" (setjd and refspectra)
+Image header keyword to be used as the sorting parameter for selection
+based on order.  The header parameter must be numeric but otherwise may
+be anything.  Common sorting parameters are times or positions.
+.le
+.ls group = "ljd" (setjd and refspectra)
+Image header keyword to be used to group spectra.  For those selection
+methods which use the group parameter the reference and object
+spectra must have identical values for this keyword.  This can
+be anything but it must be constant within a group.  Common grouping
+parameters are the date of observation "date-obs" (provided it does not
+change over a night) or the local Julian day number.
+.le
+.ls time = no, timewrap = 17. (refspectra)
+Is the sorting parameter a 24 hour time?  If so then the time origin
+for the sorting is specified by the timewrap parameter.  This time
+should precede the first observation and follow the last observation
+in a 24 hour cycle.
+.le
+
+.ce
+-- DISPERSION  CORRECTION PARAMETERS --
+.ls linearize = yes (dispcor)
+Interpolate the spectra to a linear dispersion sampling?  If yes the
+spectra will be interpolated to a linear or log linear sampling using
+the linear dispersion parameters specified by other parameters.  If
+no the nonlinear dispersion function(s) from the dispersion function
+database are assigned to the input image world coordinate system
+and the spectral data is not interpolated.  Note the interpolation
+function type is set by the package parameter \fIinterp\fR.
+.le
+.ls log = no (ecdispcor)
+Use linear logarithmic wavelength coordinates?  Linear logarithmic
+wavelength coordinates have wavelength intervals which are constant
+in the logarithm of the wavelength.
+.le
+.ls flux = yes (ecdispcor)
+Conserve the total flux during interpolation?  If \fIno\fR the output
+spectrum is interpolated from the input spectrum at each output
+wavelength coordinate.  If \fIyes\fR the input spectrum is integrated
+over the extent of each output pixel.  This is slower than
+simple interpolation.
+.le
+
+.ce
+-- SENSITIVITY CALIBRATION PARAMETERS --
+.ls bandwidth = 10., bandsep = 10. (standard)
+Interpolated bandpass grid.  If INDEF then the same bandpasses as in the
+calibration files are used otherwise the calibration data is interpolated
+to the specified set of bandpasses.
+.le
+.ls s_interact = yes (standard)
+Display the bandpasses on the standard star data and allow interactive
+addition and deletion of bandpasses.
+.le
+.ls s_function = "spline3", s_order = 1 (sensfunc)
+Function and order used to fit the sensitivity data.  The function types are
+"chebyshev" polynomial, "legendre" polynomial, "spline3" cubic spline,
+and "spline1" linear spline.
+Order of the sensitivity fitting function.  The value corresponds to the
+number of polynomial terms or the number of spline pieces.  The default
+values may be changed interactively.
+.le
+.ls fnu = no (calibrate)
+The default calibration is into units of F-lambda. If \fIfnu\fR = yes then
+the calibrated spectrum will be in units of F-nu.
+.le
+
+.ce
+PACKAGE PARAMETERS
+.ls dispaxis = 2
+Default dispersion axis.  The dispersion axis is 1 for dispersion
+running along image lines and 2 for dispersion running along image
+columns.  If the image header parameter DISPAXIS is defined it has
+precedence over this parameter.  The default value defers to the
+package parameter of the same name.
+.le
+.ls extinction = "onedstds$kpnoextinct.dat" (standard, sensfunc, calibrate)
+Extinction file for a site.  There are two extinction files in the
+NOAO standards library, onedstds$, for KPNO and CTIO.  These extinction
+files are used for extinction and flux calibration.
+.le
+.ls caldir (standard)
+Standard star calibration directory.  A directory containing standard
+star data files.  Note that the directory name must end with '/'.
+There are a number of standard star calibrations directories in the NOAO
+standards library, onedstds$.
+.le
+.ls observatory = "observatory" (observatory)
+The default observatory to use for latitude dependent computations.
+If the OBSERVAT keyword in the image header it takes precedence over
+this parameter.
+.le
+.ls interp = "poly5" (nearest|linear|poly3|poly5|spline3|sinc) (dispcor)
+Spectrum interpolation type used when spectra are resampled.  The choices are:
+
+.nf
+        nearest - nearest neighbor
+         linear - linear
+          poly3 - 3rd order polynomial
+          poly5 - 5th order polynomial
+        spline3 - cubic spline
+           sinc - sinc function
+.fi
+.le
+.ls database = "database"
+Database name used by various tasks.  This is a directory which is created
+if necessary.
+.le
+.ls verbose = no
+Verbose output?  If set then almost all the information written to the
+logfile is also written to the terminal except when the task is a
+background or batch process.
+.le
+.ls logfile = "logfile"
+If specified detailed text log information is written to this file.
+.le
+.ls plotfile = ""
+If specified metacode plots are recorded in this file for later review.
+Since plot information can become large this should be used only if
+really desired.
+.le
+.ih
+ENVIRONMENT PARAMETERS
+The environment parameter \fIimtype\fR is used to determine the extension
+of the images to be processed and created.  This allows use with any
+supported image extension.  For STF images the extension has to be exact;
+for example "d1h".
+.ih
+DESCRIPTION
+\fBDoecslit\fR subtracts background sky or scattered light, extracts,
+wavelength calibrates, and flux calibrates multiorder echelle slit spectra
+which have been processed to remove the detector characteristics; i.e. CCD
+images have been bias, dark count, and flat field corrected.  The spectra
+should be oriented such that pixels of constant wavelength are aligned with
+the image columns or lines.  Small departures from this alignment are not
+critical resulting in only a small loss of resolution.  Single order
+observations should be reduced with \fBdoslit\fR.
+
+The task is a command language script which collects and combines the
+functions and parameters of many general purpose tasks to provide a single,
+complete data reduction path and a degree of guidance, automation, and
+record keeping.  In the following description and in the parameter section
+the various general tasks used are identified.  Further
+information about those tasks and their parameters may be found in their
+documentation.  \fBDoecslit\fR also simplifies and consolidates parameters
+from those tasks and keeps track of previous processing to avoid
+duplications.
+
+The general organization of the task is to do the interactive setup steps,
+such as the aperture definitions and reference dispersion function
+determination, first using representative calibration data and then perform
+the majority of the reductions automatically, possibly as a background
+process, with reference to the setup data.  In addition, the task
+determines which setup and processing operations have been completed in
+previous executions of the task and, contingent on the \fIredo\fR and
+\fIupdate\fR options, skip or repeat some or all the steps.
+
+The description is divided into a quick usage outline followed by details
+of the parameters and algorithms.  The usage outline is provided as a
+checklist and a refresher for those familiar with this task and the
+component tasks.  It presents only the default or recommended usage
+since there are many variations possible.
+
+\fBUsage Outline\fR
+
+.ls 6 [1]
+The images are first processed with \fBccdproc\fR for overscan,
+zero level, dark count, and flat field corrections.
+.le
+.ls [2]
+Set the \fBdoecslit\fR parameters with \fBeparam\fR.  Specify the object
+images to be processed, an aperture reference image (usually a bright
+star spectrum) to use in finding the orders and defining the
+aperture parameters, one or more arc images, and one or more standard
+star images.  If there are many object, arc, or standard star images
+you might prepare "@ files".  Set the detector and data
+specific parameters.  Select the processing options desired.
+Finally you might wish to review the \fBsparams\fR algorithm parameters
+though the defaults are probably adequate.
+.le
+.ls [3]
+Run the task.  This may be repeated multiple times with different
+observations and the task will generally only do the setup steps
+once and only process new images.  Queries presented during the
+execution for various interactive operations may be answered with
+"yes", "no", "YES", or "NO".  The lower case responses apply just
+to that query while the upper case responses apply to all further
+such queries during the current execution and no further queries of that
+type will be made.
+.le
+.ls [4]
+The specified number of orders (ranked by peak strength) in the aperture
+reference image are located and default fixed width apertures are
+assigned.  If the resize option is set the apertures are resized by finding
+the level which is 5% (the default) of the peak above local background.
+You then have the option of entering the aperture editing loop to check the
+aperture positions, sizes, and background fitting parameters.  This is
+highly recommended.  Note that it is important that the aperture numbers be
+sequential with the orders and if any orders are skipped the aperture
+numbers should also skip.  It is also important to verify the background
+regions with the 'b' key.  Usually you want any changes made to the
+background definitions to apply to all apertures so use the 'a' key to
+select all apertures before modifying the background parameters.  To exit
+the background mode and then to exit the review mode use 'q'.
+.le
+.ls [5]
+The order positions at a series of points along the dispersion are measured
+and a function is fit to these positions.  This may be done interactively
+to examine the traced positions and adjust the fitting parameters.  To exit
+the interactive fitting type 'q'.  Not all orders need be examined and the
+"NO" response will quit the interactive fitting using the last defined
+fitting parameters on the remaining traces.
+.le
+.ls [6]
+Apertures are now defined for all standard and object images.  This is only
+done if there are no previous aperture definitions for the image.  The
+aperture references previously defined are used as the initial set of
+apertures for each image.  The apertures are then recentered by an average
+shift over all orders and resized if that option is selected.
+The apertures may also be retraced and interactively examined
+for each image if the tracing option is selected and quicklook mode is not.
+.le
+.ls [7]
+If scattered light subtraction is selected the scattered light parameters
+are set using the aperture reference image and the task \fBapscatter\fR.
+The purpose of this is to interactively define the aperture buffer distance
+for the scattered light and the cross and parallel dispersion fitting
+parameters.  The fitting parameters are taken from and recorded in the
+parameter sets \fBapscat1\fR and \fBapscat2\fR.  All other scattered light
+subtractions are done noninteractively with these parameters.  Note that
+the scattered light correction modifies the input images.  Scattered light
+subtraction is not done in quicklook mode.
+.le
+.ls [8]
+If dispersion correction is selected the first arc in the arc list is
+extracted.  The dispersion function is defined using the task
+\fBecidentify\fR.  Identify a few arc lines in a few orders with 'm' and
+'o' and use the 'l' line list identification command to automatically add
+additional lines and fit the dispersion function.  Check the quality of the
+dispersion function fit with 'f'.  When satisfied exit with 'q'.
+.le
+.ls [9]
+If the flux calibration option is selected the standard star spectra are
+processed (if not done previously).  The images are background subtracted,
+extracted, and wavelength calibrated.  The appropriate arc
+calibration spectra are extracted and the dispersion function refit
+using the arc reference spectrum as a starting point.  The standard star
+fluxes through the calibration bandpasses are compiled.  You are queried
+for the name of the standard star calibration data file.  Because echelle
+spectra are often at much higher dispersion than the calibration data,
+interpolated bandpasses may be defined with the bandpass parameters in
+\fBsparams\fR and checked or modified interactively.
+
+After all the standard stars are processed a sensitivity function is
+determined using the interactive task \fBsensfunc\fR.  Finally, the
+standard star spectra are extinction corrected and flux calibrated
+using the derived sensitivity function.
+.le
+.ls [10]
+The object spectra are now automatically background subtracted
+(an alternative to scattered light subtraction),
+extracted, wavelength calibrated, and flux calibrated.
+.le
+.ls [11]
+The option to examine the final spectra with \fBsplot\fR may be given.
+To exit type 'q'.  In quicklook mode the spectra are plotted
+noninteractively with \fBspecplot\fR.
+.le
+.ls [12]
+The final spectra will have the same name as the original 2D images
+with a ".ec" extension added.
+.le
+
+\fBSpectra and Data Files\fR
+
+The basic input consists of echelle slit object, standard star, and arc
+calibration spectra stored as IRAF images.
+The type of image format is defined by the
+environment parameter \fIimtype\fR.  Only images with that extension will
+be processed and created.
+The raw CCD images must be
+processed to remove overscan, bias, dark count, and flat field effects.
+This is generally done using the \fBccdred\fR package.  Flat fields which
+are not contaminated by low counts between the apertures may be prepared
+with the task \fBapflatten\fR (recommended) or \fBapnormalize\fR.  Lines of
+constant wavelength across the orders should be closely aligned with one of
+the image axes.  Sometimes the orders are aligned rather than the spectral
+features.  This will result in a small amount of resolution loss but is
+often acceptable.  In some cases one may correct for misalignment with the
+\fBrotate\fR task.  More complex geometric problems and observations of
+extended objects should be handled by the \fBlongslit\fR package and single
+order observations should be processed by \fBdoslit\fR.
+
+The aperture reference spectrum is generally a bright star.  The arc
+spectra are comparison arc lamp observations (they must all be of the same
+type).  The assignment of arc calibration exposures to object exposures is
+generally done by selecting the nearest in time and interpolating.
+However, the optional \fIarc assignment table\fR may be used to explicitly
+assign arc images to specific objects.  The format of this file is
+described in task \fBrefspectra\fR.
+
+The final reduced spectra are recorded in two or three dimensional IRAF
+images.  The images have the same name as the original images with an added
+".ec" extension.  Each line in the reduced image is a one dimensional
+spectrum with associated aperture, order, and wavelength
+information.  When the \fIextras\fR parameter is set the lines in the
+third dimension contain additional information (see
+\fBapsum\fR for further details).  These spectral formats are accepted by the
+one dimensional spectroscopy tasks such as the plotting tasks \fBsplot\fR
+and \fBspecplot\fR.  The special task \fBscopy\fR may be used to extract
+specific apertures or to change format to individual one dimensional
+images.  The task \fBscombine\fR is used to combine or merge orders into
+a single spectrum.
+
+\fBPackage Parameters\fR
+
+The \fBechelle\fR package parameters set parameters which change
+infrequently and define the standard I/O functions.  The extinction file
+is used for making extinction corrections and the standard star
+calibration directory is used for determining flux calibrations from
+standard star observations.  The calibration directories contain data files
+with standard star fluxes and band passes.  The available extinction
+files and flux calibration directories may be listed using the command:
+.nf
+
+	cl> page onedstds$README
+
+.fi
+The extinction correction requires computation of an air mass using the
+task \fBsetairmass\fR.  The air mass computation needs information
+about the observation and, in particular, the latitude of the observatory.
+This is determined using the OBSERVAT image header keyword.  If this
+keyword is not present the observatory parameter is used.  See the
+task \fBobservatory\fR for more on defining the observatory parameters.
+
+The spectrum interpolation type is used whenever a spectrum needs to be
+resampled for linearization or performing operations between spectra
+with different sampling.  The "sinc" interpolation may be of interest
+as an alternative but see the cautions given in \fBonedspec.package\fR.
+
+The verbose parameter selects whether to print everything which goes
+into the log file on the terminal.  It is useful for monitoring
+what the \fBdoecslit\fR task does.  The log and plot files are useful for
+keeping a record of the processing.  A log file is highly recommended.
+A plot file provides a record of the apertures, traces, and extracted
+spectra but can become quite large.
+The plotfile is most conveniently viewed and printed with \fBgkimosaic\fR.
+
+\fBProcessing Parameters\fR
+
+The input images are specified by image lists.  The lists may be
+a list of explicit comma separate image names, @ files, or image
+templates using pattern matching against file names in the directory.
+To allow wildcard image lists to be used safely and conveniently the
+image lists are checked to remove extracted images (the .ec images)
+and to automatically identify object and arc spectra.  Object and arc
+images are identified by the keyword IMAGETYP with values of "object",
+"OBJECT", "comp", or "COMPARISON" (the current practice at NOAO).
+If arc images are found in the object list they are transferred to the
+arc list while if object images are found in the arc list they are ignored.
+All other image types, such as biases, darks, or flat fields, are
+ignored.  This behavior allows simply specifying all images with a wildcard
+in the object list with automatic selections of arc spectra or a
+wildcard in the arc list to automatically find the arc spectra.
+If the data lack the identifying information it is up to the user
+to explicitly set the proper lists.
+
+As mentioned earlier, all the arc images must be of the same type;
+that is taken with the same arc lamp.  The aperture reference parameter
+is a single image name which is usually a bright star.
+
+The next set of parameters describe the noise characteristics and the
+general layout of the orders.  The read out noise and gain are used when
+"cleaning" cosmic rays and when using variance or optimal weighting.  These
+parameters must be fairly accurate.  Note that these are the effective
+parameters and must be adjusted if previous processing has modified the
+pixel values; such as with an unnormalized flat field.
+
+The general direction in which the orders run is specified by the
+dispersion axis parameter.  Recall that ideally it is the direction
+of constant wavelength which should be aligned with an image axis and
+the dispersion direction will not be aligned because of the cross-dispersion.
+The \fInorders\fR parameter is used to automatically find the orders.  The
+specified number of the brightest peaks are found.  Generally after finding the
+orders the aperture definitions are reviewed and adjusted interactively.
+The profile width should be approximately the full width at the profile
+base.  The default aperture limits and background regions are all
+derived from this width parameter.
+
+The next set of parameters select the processing steps and options.  The
+various calibration steps may be done simultaneously, that is at the same
+time as the basic extractions, or in separate executions of the task.
+Typically, all the desired operations are done at the same time.
+Dispersion correction requires at least one arc spectrum and flux
+calibration requires dispersion correction and at least one standard star
+observation.
+
+The \fIresize\fR option resets the edges of the extraction apertures based
+on the profile for each object and standard star order.  The default
+resizing is to the 5% point relative to the peak measured above the
+background.  This allows following changes in the seeing.  However, one
+should consider the consequences of this if attempting to flux calibrate
+the observations.  Except in quicklook mode, the apertures for each object
+and standard star observation may be reviewed graphically and further
+adjustments made to the aperture width and background regions.
+
+The apertures for each observation are adjusted for small shifts relative
+to the reference aperture definitions.  If you think this is not sufficient,
+say to account for rotation of the detector or for differing atmospheric
+dispersion, the \fItrace\fR option allows redefining the aperture trace
+functions for each observation.  Note this is only allowed in non-quicklook
+mode.
+
+The \fIclean\fR option invokes a profile
+fitting and deviant point rejection algorithm as well as a variance weighting
+of points in the aperture.  See the next section for more about
+requirements to use this option.
+
+The \fIbackground\fR option selects a type of correction for background
+or scattered light.  If the type is "scattered" a global scattered light
+is fit to the data between the apertures  and subtracted from the images.
+\fINote that the input images are modified by this operation\fR.
+This option is slow and is not allowed in quicklook
+mode.  Alternatively, a local background may be subtracted using
+background regions defined for each aperture.  The background may be
+within the slit for a sky subtraction or outside of the slit for a
+local scattered light subtraction.  The data in the regions
+may be averaged, medianed, or the minimum value used.  Another choice
+is to fit the data in the background regions by a function and interpolate
+to the object aperture.
+
+Generally once a spectrum has been processed it will not be reprocessed if
+specified as an input spectrum.  However, changes to the underlying
+calibration data can cause such spectra to be reprocessed if the
+\fIupdate\fR flag is set.  The changes which will cause an update are a new
+reference image, adding the scattered light subtraction option, a new arc
+reference image, and new standard stars.  If all input spectra are to be
+processed regardless of previous processing the \fIredo\fR flag may be
+used.  Note that reprocessing clobbers the previously processed output
+spectra.
+
+The final step is to plot the spectra if the \fIsplot\fR option is
+selected.  In non-quicklook mode there is a query which may be
+answered either in lower or upper case.  The plotting uses the interactive
+task \fBsplot\fR.  In quicklook mode the plot appears noninteractively
+using the task \fBspecplot\fR.  
+
+The \fIquicklook\fR option provides a simpler, less interactive, mode.
+The quicklook mode automatically assigns the reference apertures to
+the object and standard star observations without interactive review
+or tracing, does not do the time consuming scattered light correction,
+and the \fIsplot\fR option selects a noninteractive plot to be
+shown at the end of processing of each object and standard star
+spectrum.  While the algorithms used in quicklook mode are nearly the same
+as in non-quicklook mode and the final results may be the same it is
+recommended that the greater degree of monitoring and review in
+non-quicklook mode be used for careful final reductions.
+
+The batch processing option allows object spectra to be processed as a
+background or batch job.  This will occur only if the interactive
+\fIsplot\fR option is not active; either not set, turned off during
+processing with "NO", or in quicklook mode.  In batch processing the
+terminal output is suppressed.
+
+The \fIlistonly\fR option prints a summary of the processing steps
+which will be performed on the input spectra without actually doing
+anything.  This is useful for verifying which spectra will be affected
+if the input list contains previously processed spectra.  The listing
+does not include any arc spectra which may be extracted to dispersion
+calibrate an object spectrum.
+
+The last parameter (excluding the task mode parameter) points to
+another parameter set for the algorithm parameters.  The default
+parameter set is called \fBsparams\fR.  The algorithm parameters are
+discussed further in the next section.
+
+\fBAlgorithms and Algorithm Parameters\fR
+
+This section summarizes the various algorithms used by the
+\fBdoecslit\fR task and the parameters which control and modify the
+algorithms.  The algorithm parameters available to you are
+collected in the parameter set \fBsparams\fR.  These parameters are
+taken from the various general purpose tasks used by the \fBdoecslit\fR
+processing task.  Additional information about these parameters and
+algorithms may be found in the help for the actual
+task executed.  These tasks are identified below.  The aim of this
+parameter set organization is to collect all the algorithm parameters
+in one place separate from the processing parameters and include only
+those which are relevant for echelle slit data.  The parameter values
+can be changed from the defaults by using the parameter editor,
+.nf
+
+cl> epar sparams
+
+.fi
+or simple typing \fIsparams\fR.
+The parameter editor can also be entered when editing the \fBdoecslit\fR
+parameters by typing \fI:e\fR when positioned at the \fIsparams\fR
+parameter.
+
+\fBAperture Definitions\fR
+
+The first operation is to define the extraction apertures, which include the
+aperture width, background regions, and position dependence with
+wavelength, for the input echelle slit spectra and, if flux calibration is
+selected, the standard star spectra.  This is done only for spectra which
+do not have previously defined apertures unless the \fIredo\fR option is
+set to force all definitions to be redone.  Thus, apertures may be
+defined separately using the \fBapextract\fR tasks.  This is particularly
+useful if one needs to use reference images to define apertures for very
+weak spectra which are not well centered or traced by themselves.
+
+Initially apertures are defined for a specified \fIaperture reference\fR
+image.  The selected number of orders are found automatically by selecting
+the highest peaks in a cut across the dispersion.  Apertures are assigned
+with a width given by the \fIwidth\fR parameter and numbered sequentially.
+The background regions are also defined in terms of the width parameter
+starting at one width distance from the profile center and extending to two
+widths on both sides of the profile.  As an example, if the width parameter
+is 5 pixels the default aperture limits are +/- 2.5 pixels and the
+background sample regions will be "-10:-5,5:10".  If the \fIresize\fR
+parameter is set the aperture limits are adjusted to a specified point on
+the spectrum profile (see \fBapresize\fR).
+
+A query is then given allowing the aperture definitions to be reviewed and
+modified.  Queries made by \fBdoecslit\fR generally may be answered with either
+lower case "yes" or "no" or with upper case "YES" or "NO".  The upper
+case responses apply to all further queries and so are used to eliminate
+further queries of that kind.
+
+Reviewing the aperture definitions is highly recommended to check the
+aperture numbering, aperture limits, and background regions.  The aperture
+numbers must be linearly related, with a slope of +/- 1, to the true order
+numbers though absolute order numbers need not be known.  The key point is
+that if an order is skipped the aperture numbers must also skip.  The
+background regions are checked with the 'b' key.  Typically one adjusts all
+the background regions at the same time by selecting all apertures with
+the 'a' key first.  To exit the background and aperture editing steps type
+'q'.
+
+Next the positions of the orders at various points along the dispersion
+are measured and "trace functions" are fit.  The user is asked whether
+to fit each trace function interactively.  This is selected to adjust
+the fitting parameters such as function type and order.  When
+interactively fitting a query is given for each aperture.  After the
+first aperture one may skip reviewing the other traces.
+
+After the aperture reference image is done all the object and standard star
+images are checked for aperture definitions and those without definitions
+are assigned apertures.  The assignment consists of inheriting the aperture
+from the reference aperture image, recentering the apertures based on an
+average shift that best centers all the apertures, resizing the apertures
+if the resize option is selected, and retracing the spectral orders if the
+retracing option is selected.  Retracing is only allowed in non-quicklook
+mode (set by the \fIquicklook\fR parameter).  Also interactive review of
+the aperture definitions is only done in
+non-quicklook mode.  In quicklook mode the aperture definitions are all set
+noninteractively without retracing.  It is recommended that quicklook only
+be used for initial quick extractions and calibration and that for final
+reductions one at least review the aperture definitions and possibly
+retrace each observation.
+
+The above steps are all performed using tasks from the \fBapextract\fR
+package and parameters from the \fBsparams\fR parameters.  As a quick
+summary, the dispersion direction of the spectra are determined from the
+package \fBdispaxis\fR parameter if not defined in the image header.  The default
+line or column for finding the object position on the slit and the number
+of image lines or columns to sum are set by the \fIline\fR and \fInsum\fR
+parameters.  A line of INDEF (the default) selects the middle of the
+image.  The automatic finding algorithm is described for the task
+\fBapfind\fR and basically finds the strongest peaks.  The resizing is
+described in the task \fBapresize\fR and the parameters used are also
+described there.  The tracing is
+done as described in \fBaptrace\fR and consists of stepping along the image
+using the specified \fIt_step\fR parameter.  The function fitting uses the
+\fBicfit\fR commands with the other parameters from the tracing section.
+
+\fBBackground or Scattered Light Subtraction\fR
+
+In addition to not subtracting any sky or scattered light there are two
+approaches to subtracting background light.  The first is to determine
+a smooth global scattered light component.  The second is to subtract
+a locally determined background at each point along the dispersion and
+for each aperture.  This can be either for a sky subtraction if the
+background regions are within the slit or scattered light if the
+background regions are outside of the slit.  Note that background
+subtraction is only done for object and standard star images and not
+for arc spectra.  Also, the global scattered light option is not done
+in quicklook mode.
+
+The global scattered light fitting and subtraction is done with the task
+\fBapscatter\fR.  The function fitting parameters are set interactively
+using the aperture reference spectrum.  All other subtractions are done
+noninteractively with the same set of parameters.  The scattered light is
+subtracted from the input images, thus modifying them, and one might wish
+to first make backups of the original images.
+
+The scattered light is measured between the apertures using a specified
+buffer distance from the aperture edges.  The scattered light pixels are
+fit by a series of one dimensional functions across the dispersion.  The
+independent fits are then smoothed along the dispersion by again fitting
+low order functions.  These fits then define the smooth scattered light
+surface to be subtracted from the image.  The fitting parameters are
+defined and recorded in the two parameter sets \fIapscat1\fR and
+\fIapscat2\fR.  The scattered light algorithm is described more fully in
+\fBapscatter\fR.  This algorithm is relatively slow.
+
+Local background subtraction is done during extraction based on background
+regions and parameters defined by the default background parameters or
+changed during interactive review of the apertures.  The background
+subtraction options are to subtract the average, median, or minimum of the
+pixels in the background regions, or to fit a function and subtract the
+function from under the extracted object pixels.  The background regions
+are specified in pixels from the aperture center and follow changes in
+center of the spectrum along the dispersion.  The syntax is colon separated
+ranges with multiple ranges separated by a comma or space.  The background
+fitting uses the \fBicfit\fR routines which include medians, iterative
+rejection of deviant points, and a choice of function types and orders.
+Note that it is important to use a method which rejects cosmic rays such as
+using either medians over all the background regions (\fIbackground\fR =
+"median") or median samples during fitting (\fIb_naverage\fR < -1).  The
+background subtraction algorithm and options are described in greater
+detail in \fBapsum\fR and \fBapbackground\fR.
+
+\fBExtraction\fR
+
+The actual extraction of the spectra is done by summing across the
+fixed width apertures at each point along the dispersion.
+The default is to simply sum the pixels using
+partial pixels at the ends.  There is an option to weight the
+sum based on a Poisson variance model using the \fIreadnoise\fR and
+\fIgain\fR detector parameters.  Note that if the \fIclean\fR
+option is selected the variance weighted extraction is used regardless
+of the \fIweights\fR parameter.  The sigma thresholds for cleaning
+are also set in the \fBsparams\fR parameters.
+
+The cleaning and variance weighting options require knowing the effective
+(i.e. accounting for any image combining) read out noise and gain.
+These numbers need to be adjusted if the image has been processed
+such that the intensity scale has a different origin (such as
+a scattered light subtraction) or scaling (such as caused by unnormalized
+flat fielding).  These options also require using background subtraction
+if the profile does not go to zero.  For optimal extraction and
+cleaning to work it is recommended that any flat fielding be done
+using flat fields produced by \fBapflatten\fR, no scattered light
+correction, and using background subtraction if there is any
+appreciable sky or to compensate for scattered light.
+For further discussion of cleaning and variance weighted extraction see
+\fBapvariance\fR and \fBapprofiles\fR as well as  \fBapsum\fR.
+
+\fBDispersion Correction\fR
+
+If dispersion correction is not selected, \fIdispcor\fR=no, then the object
+spectra are simply extracted.  The extracted spectra may be plotted
+by setting the \fIsplot\fR option.  This produces a query and uses
+the interactive \fBsplot\fR task in non-quicklook mode and uses
+\fBspecplot\fR noninteractively in quicklook mode.
+
+Dispersion corrections are applied to the extracted spectra if the
+\fIdispcor\fR processing parameter is set.  There
+are three basic steps involved; determining the dispersion functions
+relating pixel position to wavelength, assigning the appropriate
+dispersion function to a particular observation, and either storing
+the nonlinear dispersion function in the image headers or resampling the
+spectra to evenly spaced pixels in wavelength.
+
+The first arc spectrum in the arc list is used to define the reference
+dispersion solution.  It is extracted using the reference aperture definition.
+Note extractions of arc spectra are not background or scattered light
+subtracted.  The interactive task \fBecidentify\fR is used to define the
+dispersion function.  The idea is to mark some lines in a few orders whose
+wavelengths are known (with the line list used to supply additional lines after
+the first few identifications define the approximate wavelengths) and to fit a
+function giving the wavelength from the aperture number and pixel position.
+
+The arc dispersion function parameters are for \fBecidentify\fR and it's
+related partner \fBecreidentify\fR.  The parameters define a line list for
+use in automatically assigning wavelengths to arc lines, a centering width
+(which should match the line widths at the base of the lines), the
+dispersion function type and orders, parameters to exclude bad lines from
+function fits, and defining whether to refit the dispersion function as
+opposed to simply determining a zero point shift.  The defaults should
+generally be adequate and the dispersion function fitting parameters may be
+altered interactively.  One should consult the help for the two tasks for
+additional details of these parameters and the interactive operation of
+\fBecidentify\fR.
+
+Once the reference dispersion function is defined other arc spectra are
+extracted as required by the object spectra.  The assignment of arcs is
+done either explicitly with an arc assignment table (parameter
+\fIarctable\fR) or based on a header parameter such as a time.
+This assignments are made by the task
+\fBrefspectra\fR.  When two arcs are assigned to an object spectrum an
+interpolation is done between the two dispersion functions.  This makes an
+approximate correction for steady drifts in the dispersion.
+
+The tasks \fBsetjd\fR and \fBsetairmass\fR are automatically run on all
+spectra.  This computes and adds the header parameters for the Julian date
+(JD), the local Julian day number (LJD), the universal time (UTMIDDLE), and
+the air mass at the middle of the exposure.  The default arc assignment is
+to use the Julian date grouped by the local Julian day number.  The
+grouping allows multiple nights of data to be correctly assigned at the
+same time.
+
+In non-quicklook mode the arc spectra assigned to each object are
+extracted using the same apertures as the object.  This accounts for
+changes in the recentering, aperture sizes, and tracing functions.
+In quicklook mode the arc spectra are extracted using the reference
+apertures.  When the same arc is used for several object images this
+allows the arc spectrum to only be extracted once.
+
+Defining the dispersion function for a new arc extraction is done with
+the task \fBecreidentify\fR.  This is done noninteractively with log
+information recorded about the line reidentifications and the fit.
+
+The last step of dispersion correction is setting the dispersion
+of the object image from the arc images.  There are two choices here.
+If the \fIlinearize\fR parameter is not set the nonlinear dispersion
+function is stored in the image header.  Other IRAF tasks interpret
+this information when dispersion coordinates are needed for plotting
+or analysis.  This has the advantage of not requiring the spectra
+to be interpolated and the disadvantage that the dispersion
+information is only understood by IRAF tasks and cannot be readily
+exported to other analysis software.
+
+If the \fIlinearize\fR parameter is set then the spectra are resampled to a
+linear dispersion relation either in wavelength or the log of the
+wavelength.  For echelle spectra each order is linearized independently so
+that the wavelength interval per pixel is different in different orders.
+This preserves most of the resolution and avoids over or under sampling of
+the highest or lowest dispersion orders.  The wavelength limits are
+taken from the limits determined from the arc reference spectrum and
+the number of pixels is the same as the original images.  The dispersion
+per pixel is then derived from these constraints.
+
+The linearization algorithm  parameters allow selecting the interpolation
+function type, whether to conserve flux per pixel by integrating across the
+extent of the final pixel, and whether to linearize to equal linear or
+logarithmic intervals.  The latter may be appropriate for radial velocity
+studies.  The default is to use a fifth order polynomial for interpolation,
+to conserve flux, and to not use logarithmic wavelength bins.  These
+parameters are described fully in the help for the task \fBdispcor\fR which
+performs the correction.
+
+\fBFlux Calibration\fR
+
+Flux calibration consists of an extinction correction and an instrumental
+sensitivity calibration.  The extinction correction only depends on the
+extinction function defined by the package parameter \fIextinct\fR and
+determination of the airmass from the header parameters (the air mass is
+computed by \fBsetairmass\fR as mentioned earlier).  The sensitivity
+calibration depends on a sensitivity calibration spectrum determined from
+standard star observations for which there are tabulated absolute fluxes.
+The task that applies both the extinction correction and sensitivity
+calibration to each extracted object spectrum is \fBcalibrate\fR.  Consult
+the manual page for this task for more information.
+
+Generation of the sensitivity calibration spectrum is done before
+processing any object spectra since it has two interactive steps and
+requires all the standard star observations.  The first step is tabulating
+the observed fluxes over the same bandpasses as the calibrated absolute
+fluxes.  For very high resolution it may be the case that the measured
+calibration bandpasses are too large or sparse.  In this case one must
+interpolate the calibration data to bandpasses appropriate for the data.
+If the bandpass widths and separations are given as INDEF then the same
+bandpasses as in the calibration file are used.  Otherwise a uniform grid
+of bandpasses is interpolated.  Using interpolated bandpasses is not
+rigorous but is sometimes the only choice for echelle spectra.
+
+The standard star tabulations are done after each standard star is
+extracted and dispersion corrected.  You are asked for the name of the
+standard star as tabulated in the absolute flux data files in the directory
+\fIcaldir\fR defined by the package parameters.  If the \fIinteract\fR
+parameter is yes the bandpasses can be displayed on the data and you can
+interactively add or delete bandpasses. The tabulation of the standard star
+observations over the standard bandpasses is done by the task
+\fBstandard\fR.  The tabulated data is stored in the file \fIstd\fR.  Note
+that if the \fIredo\fR flag is not set any new standard stars specified in
+subsequent executions of \fBdoecslit\fR are added to the previous data in
+the data file, otherwise the file is first deleted.  Modification of the
+tabulated standard star data, such as by adding new stars, will cause any
+spectra in the input list which have been previously calibrated to be
+reprocessed if the \fIupdate\fR flag is set.
+
+After the standard star calibration bandpass fluxes are tabulated the
+information from all the standard stars is combined to produce a
+sensitivity function for use by \fBcalibrate\fR.  The sensitivity function
+determination is interactive and uses the task \fBsensfunc\fR.  This task
+allows fitting a smooth sensitivity function to the ratio of the observed
+to calibrated fluxes verses wavelength.  The types of manipulations one
+needs to do include deleting bad observations, possibly removing variable
+extinction (for poor data), and possibly deriving a revised extinction
+function.  This is a complex operation and one should consult the manual
+page for \fBsensfunc\fR.  The sensitivity function is saved as one
+dimensional spectra (one per order) with the root name \fIsens\fR.
+Deletion of these images will also cause reprocessing to occur if the
+\fIupdate\fR flag is set.
+.ih
+EXAMPLES
+1.  The following example uses artificial data and may be executed
+at the terminal (with IRAF V2.10).  This is similar to the sequence
+performed by the test procedure "demos doecslit".
+
+.nf
+ec> demos mkecslit
+Creating example longslit in image demoobj ...
+Creating example longslit in image demostd ...
+Creating example longslit in image demoarc ...
+ec> echelle.verbose=no
+ec> echelle.caldir=onedstds$spechayescal/
+ec> doecslit Bdemoobj apref=Bdemostd arcs=Bdemoarc stand=Bdemostd \
+>>> norders=3 extcor+ fluxcal+ resize+ splot+
+Set reference aperture for Bdemostd
+Edit apertures for Bdemostd?  (yes):
+<Check background with 'b', exit background and review with 'q'>
+Fit traced positions for Bdemostd interactively?  (yes):  
+Fit curve to aperture 1 of Bdemostd interactively  (yes):
+<Exit with 'q'>
+Fit curve to aperture 2 of Bdemostd interactively  (yes): N
+Edit apertures for Bdemoobj?  (yes):
+<Check background with 'b', exit background and review with 'q'>
+Fit traced positions for Bdemoobj interactively?  (yes): N
+Extract arc reference image Bdemoarc
+Determine dispersion solution for Bdemoarc
+<Type 'm' at first strong line (pixel 156) and identify it as 4965>
+<Type 'k' to go to next order>
+<Mark 52->5002, 74->5003.6, 155->5009.3>
+<Type 'k' to go to next order and mark 18->5044.7, 231->5059.8>
+<Type 'f' to see the fit residuals>
+<Type 'q' to quit fit and then 'q' to exit>
+Extract standard star spectrum Bdemostd
+Assign arc spectra for Bdemostd
+Extract and reidentify arc spectrum Bdemoarc
+Dispersion correct Bdemostd
+B...ec.imh: ap = 1, w1 = 4953.9, w2 = 4972.2, dw = 0.071, nw = 256
+B...ec.imh: ap = 2, w1 = 4998.3, w2 = 5016.5, dw = 0.071, nw = 256
+B...ec.imh: ap = 3, w1 = 5043.5, w2 = 5061.6, dw = 0.070, nw = 256
+Compile standard star fluxes for Bdemostd
+Bdemostd.ec.imh[1]: Artificial Echelle Spectrum
+Star name in calibration list: hz14
+Bdemostd.ec.imh[1]: Edit bandpasses? (no|yes|NO|YES|NO!|YES!) (no): y
+<Exit with 'q'>
+Bdemostd.ec.imh[2]: Artificial Echelle Spectrum
+Bdemostd.ec.imh[2]: Edit bandpasses? (no|yes|NO|YES|NO!|YES!) (y): N
+Bdemostd.ec.imh[3]: Artificial Echelle Spectrum
+Bdemostd.ec.imh[3]: Edit bandpasses? (no|yes|NO|YES|NO!|YES!) (N):
+Compute sensitivity function
+Fit aperture 1 interactively? (no|yes|NO|YES) (no|yes|NO|YES) (yes):
+<Exit with 'q'>
+Sensitivity function for aperture  1 --> sens.0001
+Fit aperture 2 interactively? (no|yes|NO|YES) (no|yes|NO|YES) (yes): N
+Sensitivity function for aperture  2 --> sens.0002
+Sensitivity function for aperture  3 --> sens.0003
+Flux and/or extinction calibrate standard stars
+Standard stars:
+Splot spectrum? (no|yes|NO|YES) (yes):
+Image line/aperture to plot (0:) (1):
+<Exit with 'q'>
+Extract object spectrum Bdemoobj
+Assign arc spectra for Bdemoobj
+Extract and reidentify arc spectrum Bdemoarc
+Dispersion correct Bdemoobj
+B...ec.imh: ap = 1, w1 = 4953.9, w2 = 4972.2, dw = 0.071, nw = 256
+B...ec.imh: ap = 2, w1 = 4998.3, w2 = 5016.5, dw = 0.071, nw = 256
+B...ec.imh: ap = 3, w1 = 5043.5, w2 = 5061.6, dw = 0.070, nw = 256
+Extinction correct Bdemoobj
+Flux calibrate Bdemoobj
+Bdemoobj.ec.imh:
+Splot spectrum? (no|yes|NO|YES) (yes):
+Image line/aperture to plot (0:) (1):
+<Exit with 'q'>
+.fi
+.ih
+REVISIONS
+.ls DOECSLIT V2.10.3
+The image format type to be
+processed is selected with the \fIimtype\fR environment parameter.  The
+dispersion axis parameter is now a package parameter.  Images will only
+be processed if the have the CCDPROC keyword.  A \fIdatamax\fR parameter
+has been added to help improve cosmic ray rejection.  A bug which
+alphabetized the arc spectra was fixed.
+.le
+.ih
+SEE ALSO
+apbackground, apedit, apfind, approfiles, aprecenter, apresize, apsum, aptrace,
+apvariance, calibrate, ccdred, center1d, ctioslit, dispcor,
+echelle.doecslit, ecidentify, ecreidentify, icfit, kpnocoude, kpnoslit,
+msred, observatory, onedspec.package, refspectra, sensfunc, setairmass, setjd,
+splot, standard
+.endhelp