IRAF help page for package noao.imred.echelle, program doecslit

• objects
• apref =
• arcs = (at least one if dispersion correcting)
• arctable = (optional) (refspectra)
• standards = (at least one if flux calibrating)
• readnoise = 0., gain = 1. (apsum)
• datamax = INDEF (apsum.saturation)
• norders = 10 (apfind)
• width = 5. (apedit)
• dispcor = yes
• extcor = no
• fluxcal = no
• resize = no (apresize)
• clean = no (apsum)
• trace = yes (non-quicklook mode only) (aptrace)
• background = none (apsum, apscatter)
• splot = no
• redo = no
• update = no
• quicklook = no
• batch = no
• listonly = no
• sparams = (pset)

• line = INDEF, nsum = 10
• extras = no (apsum)

• ylevel = 0.05 (apresize)

• t_step = 10 (aptrace)
• t_function = spline3 , t_order = 2 (aptrace)
• t_niterate = 1, t_low = 3., t_high = 3. (aptrace)

• b_function = legendre , b_order = 1 (apsum)
• b_naverage = -100 (apsum)
• b_niterate = 0 (apsum)
• b_low_reject = 3., b_high_reject = 3. (apsum)
• buffer = 1. (apscatter)
• apscat1 = , apscat2 = (apscatter)

• weights = none (apsum) (none|variance)
• none
• variance
• pfit = fit1d (apsum and approfile) (fit1d|fit2d)
• lsigma = 3., usigma = 3. (apsum)

• coordlist = linelist$thar.dat (ecidentify)
• match = 1. (ecidentify)
• fwidth = 4. (ecidentify)
• cradius = 10. (reidentify)
• i_function = legendre , i_xorder = 3, i_yorder = 3 (ecidentify)
• i_niterate = 3, i_low = 3.0, i_high = 3.0 (ecidentify)
• refit = yes (ecreidentify)

• select = interp (refspectra)
• average
• following
• interp
• match
• nearest
• preceding
• sort = jd (setjd and refspectra)
• group = ljd (setjd and refspectra)
• time = no, timewrap = 17. (refspectra)

• linearize = yes (dispcor)
• log = no (ecdispcor)
• flux = yes (ecdispcor)

• bandwidth = 10., bandsep = 10. (standard)
• s_interact = yes (standard)
• s_function = spline3 , s_order = 1 (sensfunc)
• fnu = no (calibrate)

• dispaxis = 2
• extinction = onedstds$kpnoextinct.dat (standard, sensfunc, calibrate)
• caldir (standard)
• observatory = observatory (observatory)
• interp = poly5 (nearest|linear|poly3|poly5|spline3|sinc) (dispcor)
• database = database
• verbose = no
• logfile = logfile
• plotfile =

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• DOECSLIT V2.10.3

doecslit objects

Doecslit 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 doslit.

objects

apref =

arcs = (at least one if dispersion correcting)

arctable = (optional) (refspectra)

standards = (at least one if flux calibrating)

readnoise = 0., gain = 1. (apsum)

datamax = INDEF (apsum.saturation)

norders = 10 (apfind)

width = 5. (apedit)

dispcor = yes

extcor = no

fluxcal = no

resize = no (apresize)

clean = no (apsum)

trace = yes (non-quicklook mode only) (aptrace)

background = none (apsum, apscatter)

splot = no

redo = no

update = no

quicklook = no

batch = no

listonly = no

sparams = (pset)

extras = no (apsum)

t_function = spline3 , t_order = 2 (aptrace)

t_niterate = 1, t_low = 3., t_high = 3. (aptrace)

b_naverage = -100 (apsum)

b_niterate = 0 (apsum)

b_low_reject = 3., b_high_reject = 3. (apsum)

buffer = 1. (apscatter)

apscat1 = , apscat2 = (apscatter)

variance

pfit = fit1d (apsum and approfile) (fit1d|fit2d)

lsigma = 3., usigma = 3. (apsum)

match = 1. (ecidentify)

fwidth = 4. (ecidentify)

cradius = 10. (reidentify)

i_function = legendre , i_xorder = 3, i_yorder = 3 (ecidentify)

i_niterate = 3, i_low = 3.0, i_high = 3.0 (ecidentify)

refit = yes (ecreidentify)

following

interp

match

nearest

preceding

sort = jd (setjd and refspectra)

group = ljd (setjd and refspectra)

time = no, timewrap = 17. (refspectra)

log = no (ecdispcor)

flux = yes (ecdispcor)

s_interact = yes (standard)

s_function = spline3 , s_order = 1 (sensfunc)

fnu = no (calibrate)

extinction = onedstds$kpnoextinct.dat (standard, sensfunc, calibrate)

caldir (standard)

observatory = observatory (observatory)

interp = poly5 (nearest|linear|poly3|poly5|spline3|sinc) (dispcor)

        nearest - nearest neighbor
         linear - linear
          poly3 - 3rd order polynomial
          poly5 - 5th order polynomial
        spline3 - cubic spline
           sinc - sinc function

verbose = no

logfile = logfile

plotfile =

The environment parameter imtype 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".

Doecslit 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 doslit.

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. Doecslit 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 redo and update 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.

Usage Outline

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After all the standard stars are processed a sensitivity function is determined using the interactive task sensfunc. Finally, the standard star spectra are extinction corrected and flux calibrated using the derived sensitivity function.

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Spectra and Data Files

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 imtype. 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 ccdred package. Flat fields which are not contaminated by low counts between the apertures may be prepared with the task apflatten (recommended) or apnormalize. 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 rotate task. More complex geometric problems and observations of extended objects should be handled by the longslit package and single order observations should be processed by doslit.

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 arc assignment table may be used to explicitly assign arc images to specific objects. The format of this file is described in task refspectra.

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 extras parameter is set the lines in the third dimension contain additional information (see apsum for further details). These spectral formats are accepted by the one dimensional spectroscopy tasks such as the plotting tasks splot and specplot. The special task scopy may be used to extract specific apertures or to change format to individual one dimensional images. The task scombine is used to combine or merge orders into a single spectrum.

Package Parameters

The echelle 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:

	cl> page onedstds$README

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 onedspec.package.

The verbose parameter selects whether to print everything which goes into the log file on the terminal. It is useful for monitoring what the doecslit 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 gkimosaic.

Processing Parameters

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 norders 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 resize 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 trace option allows redefining the aperture trace functions for each observation. Note this is only allowed in non-quicklook mode.

The clean 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 background 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. Note that the input images are modified by this operation. 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 update 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 redo flag may be used. Note that reprocessing clobbers the previously processed output spectra.

The final step is to plot the spectra if the splot 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 splot. In quicklook mode the plot appears noninteractively using the task specplot.

The quicklook 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 splot 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 splot 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 listonly 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 sparams. The algorithm parameters are discussed further in the next section.

Algorithms and Algorithm Parameters

This section summarizes the various algorithms used by the doecslit task and the parameters which control and modify the algorithms. The algorithm parameters available to you are collected in the parameter set sparams. These parameters are taken from the various general purpose tasks used by the doecslit 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,

cl> epar sparams

Aperture Definitions

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 redo option is set to force all definitions to be redone. Thus, apertures may be defined separately using the apextract 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 aperture reference 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 width 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 resize parameter is set the aperture limits are adjusted to a specified point on the spectrum profile (see apresize).

A query is then given allowing the aperture definitions to be reviewed and modified. Queries made by doecslit 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 quicklook 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 apextract package and parameters from the sparams parameters. As a quick summary, the dispersion direction of the spectra are determined from the package dispaxis 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 line and nsum parameters. A line of INDEF (the default) selects the middle of the image. The automatic finding algorithm is described for the task apfind and basically finds the strongest peaks. The resizing is described in the task apresize and the parameters used are also described there. The tracing is done as described in aptrace and consists of stepping along the image using the specified t_step parameter. The function fitting uses the icfit commands with the other parameters from the tracing section.

Background or Scattered Light Subtraction

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 apscatter. 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 apscat1 and apscat2. The scattered light algorithm is described more fully in apscatter. 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 icfit 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 (background = "median") or median samples during fitting (b_naverage < -1). The background subtraction algorithm and options are described in greater detail in apsum and apbackground.

Extraction

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 readnoise and gain detector parameters. Note that if the clean option is selected the variance weighted extraction is used regardless of the weights parameter. The sigma thresholds for cleaning are also set in the sparams 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 apflatten, 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 apvariance and approfiles as well as apsum.

Dispersion Correction

If dispersion correction is not selected, dispcor=no, then the object spectra are simply extracted. The extracted spectra may be plotted by setting the splot option. This produces a query and uses the interactive splot task in non-quicklook mode and uses specplot noninteractively in quicklook mode.

Dispersion corrections are applied to the extracted spectra if the dispcor 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 ecidentify 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 ecidentify and it's related partner ecreidentify. 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 ecidentify.

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 arctable) or based on a header parameter such as a time. This assignments are made by the task refspectra. 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 setjd and setairmass 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 ecreidentify. 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 linearize 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 linearize 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 dispcor which performs the correction.

Flux Calibration

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 extinct and determination of the airmass from the header parameters (the air mass is computed by setairmass 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 calibrate. 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 caldir defined by the package parameters. If the interact 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 standard. The tabulated data is stored in the file std. Note that if the redo flag is not set any new standard stars specified in subsequent executions of doecslit 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 update 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 calibrate. The sensitivity function determination is interactive and uses the task sensfunc. 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 sensfunc. The sensitivity function is saved as one dimensional spectra (one per order) with the root name sens. Deletion of these images will also cause reprocessing to occur if the update flag is set.

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".

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):

Fit traced positions for Bdemostd interactively?  (yes):  
Fit curve to aperture 1 of Bdemostd interactively  (yes):

Fit curve to aperture 2 of Bdemostd interactively  (yes): N
Edit apertures for Bdemoobj?  (yes):

Fit traced positions for Bdemoobj interactively?  (yes): N
Extract arc reference image Bdemoarc
Determine dispersion solution for Bdemoarc


5002, 74->5003.6, 155->5009.3>
5044.7, 231->5059.8>


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

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):

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):

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):