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% @(#)calibrirsp.hlq 19.1 (ESO-IPG) 02/25/03 14:23:15
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%++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
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%.COPYRIGHT (c) 1992 European Southern Observatory
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%.AUTHOR E.Oliva, Arcetri (Florence)
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%.KEYWORDS MIDAS, help files, CALIBRATE/IRSPEC
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%.PURPOSE On-line help file for the command: CALIBRATE/IRSPEC
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%.VERSION 1.0 22-SEP-1992 : Creation, E.Oliva
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%----------------------------------------------------------------
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CALIBRATE/IRSPEC 22-SEP-1992 EO
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Apply on-line (mechanical) wavelength calibration.
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CALIBRATE/IRSPEC ima_ref mode=define
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Define and store in ima_ref precise calibration from sky/lamp lines
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CALIBRATE/IRSPEC ima ref=ima_ref
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Apply precise wavelength calibration to frame ima from parameters
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Purpose: The wavelength dispersion on the IRSPEC array is linear within
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a small - and totally negligible - fraction of the pixel size.
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Hence, wavelength calibrating simply means modifying the x-start
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and x-step values (descriptor) of the image. Another advantage
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of IRSPEC is that one can very precisely compute (analytically)
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the pixel size - in wavelength - once the central wavelength of
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the frame is known. A quite precise - usually within 1 pixel -
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estimate of this quantity is available on-line at the instrument
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("mechanical" calibration) and is stored in the original files
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in the form of descriptors. You can directly use this information
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and determine the "mechanical" wavelength calibration as in the
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This command allows you also to determine more precisely the
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central wavelength of your frame - and hence to obtain a very
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accurate wavelength calibration - if you have a frame containing
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lines with known wavelengths; up to 2.3 microns the OH lines in
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the sky frames are a very convenient calibrator (Oliva \& Origlia,
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1992, A\&A 254, 466). See the 2-nd example and/or use
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Finally, this command can be used to apply a precise calibration
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to a given image (see third example).
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Syntax: CALIBRATE/IRSPEC ima [ref=reference_ima] [mode=calibration_mode]
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[units=wavelength_units]
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ima = Frame to wavelength calibrate, it may have any
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size in Y (could e.g. be 1D) but must have the
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original size in X. "Untouched" on exit (see last
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If mode=d (definition of precise calibration),
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"ima" is the sky/lamp frame containing lines with
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known wavelengths and must have the original X,Y
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sizes. Untouched on exit.
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ref = Optional reference image which contains precise
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calibration parameters, determined using CALIB/IRSP
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mode = If set to d (define) it interactively defines the
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best wavelength calibration parameters using the
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lines contained in the frame "ima" (see also
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TUTORIAL/CALIB). Use mode=d (or just m=d) for
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calibration using sky lines (you need a flat and
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a dark for this). For lamp lines frames it may be
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more convenient to work on the frame as it is, in
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which case use m=d1 (sorry for the dirty
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units = Wavelengths are given in microns. You can use
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units=a (or just u=a) if you prefer to work in
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Note: It is most convenient (and clearer) to apply the wavelength
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calibration only to "rectified frames" - i.e. with straight
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spectral lines (see RECTIFY/IRSPEC).
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The wavelength calibrated frame is identical to the original
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but has different start and step in X. Therefore, if you want
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to go back to the uncalibrated image it's enough using
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WRITE/DESC image_name start 1
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WRITE/DESC image_name step 1
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apply mechanical calibration to frame test4
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CALIB/IRSP sky3 mode=d
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define and store in "sky3" precise calibration parameters
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from the sky/lamp lines contained in the same frame (see
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CALIB/IRSP test4 ref=sky3
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apply precise parameters (defined above) to frame "test4"