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Raw and Quick Data Analysis

This section briefly describes procedures for a quick and crude analysis of INTEGRAL data. This is done in the IRAF environment (of which a basic knowledge is assumed).

Most of the different steps for the data reduction and analysis can be performed using standard IRAF tasks, though some particular operations require some non-standard programs. These programs have been collected into a separate package called integral (see for availability and installation instructions).

For loading the relevant (standard and non-standard) tasks type the following sequence:
cl (to start the IRAF environment)
integral (to load non-standard and standard IRAF tasks required)
int_status (to generate the files required for the 2D reconstruction)

By typing help integral opt=sys, a general description of the INTEGRAL package is printed on the display. To obtain a paper copy of this help type help integral opt=sys | lprint.

Listing INTEGRAL tasks.
When the INTEGRAL package is loaded, all non-standard tasks are showed on the display. By typing help a list of these specific tasks and a brief description of each is printed on display. The non-standard INTEGRAL tasks are the following.

Task Function
int_hart Hartmann test for a list of couples of images
int_fwhm Center, peak, sigma and FWHM of a list of 2D images for a lines array
int_stat Statistics data for a list of images
ms2ascii Convert a multispec format 2D image to ASCII format spectra
readfxcor Export to a file the values of radial velocities, pixel shifts, or widths obtained
using fxcor
int_map 2D reconstruction from a ASCII file with fibre number, x, y,
parameter to be mapped, and fiber status columns
int_rec 2D reconstruction from a non-reduced 2D image
int_spd1f Spatial shift between two images for a fibre
int_spdXf Spatial shift between two images for a fibre list
int_nspec Extract a calibrated spectrum of a selected fibre
int_xyfib Show on display xcenter (middle line in the dispersion axis) and ycenter
(spatial coordinate) of the `apfile' parameters for a selected fiber
int_daref Shifts along a.r. and dec. produced by differential atmospheric refraction

Help on integral tasks
Help is available for each task (e.g., help int_spdXf)

Some examples of the quick data examination
For a raw analysis of the images standard INTEGRAL tasks, like imexamine or implot can be used. With imexamine the user can generate profiles along the dispersion or spatial axes (type j and k respectively), contours (type e) etc. More complex operations (e.g. extraction of a fiber aperture, wavelength calibration, building up a map) require the knowledge of the standard tasks of IRAF devoted to fiber-data analysis (see, for instance, table in next section). The INTEGRAL software offers some specific tasks which can be used to obtain an extracted spectrum or a 2D reconstruction of a filter image.

2D reconstruction of a filter image

To perform a 2D reconstruction use the task int_rec. In the example below, an object image ("M32center") was taken with the sb2 bundle. Using int_rec an intensity map ("M32_300_500") between pixels 300 and 500 in the dispersion axis was obtained.

The first step of the int_rec task is the positional defining, tracing, and extraction of the apertures in the "referenceflat", unless this operation has been already done. The name of the file with the parameters corresponding to the definition, tracing and extraction is saved in the database as apnamep1_p2, where 'name' refers to the flat field image ("referenceflat" in the example), 'p1' is the value of the first pixel (parameter pix1) along the dispersion axis, and 'p2' is the value of the second pixel (parameter pix2). If this file is already in existance, the operations will not be repeated.

The definition (width and center), tracing and extraction of the apertures in "referenceflat" is done interactively. Within int_rec, this is achieved using the standard IRAF task apall. On execution, the profile of the apertures along the middle line in the dispersion axis are displayed. All apertures will appear identified and ordered, however, it is possible that a cosmic ray event has been falsely identified instead of a true aperture. In this case, this aperture should be deleted (typing d) and the true aperture marked (typing m). The rest of the apertures will then need to be selected (typing a), and ordered (typing o). Help is available on these commands by typing ?. The widths of the apertures will not have to changed.

After defining of the aperture positions, they are spectrally traced. In principle, the user can do this operation interactively (for each fibre!). Various operations are possible e.g. changing the order of the fitting polynomial etc. apall then displays the indivually extracted spectra (which may or may not be viewed).

The second step is the definition, tracing and extraction of the apertures in the object image, (in this case, "M32center"). If the previous operations have been carried out on the flat field image (with the same instrument configuration), then it is safe to assume that the same extraction parameters will apply (database file apnamep1_p2). This can then be used as a reference for tracing and extraction in other images taken during the same night because INTEGRAL/WYFFOS should be very stable. Obviously, if p1 and/or p2 are changed, a new definition, tracing and extraction paramter file is required.

The third step is the reconstruction of the image, according to a interpolation (NAG routines e01saf and e01sbf).

Note that an estimation of the BIAS is required for int_rec.

object = "M32center" Object image
flat = "referenceflat" Flat image
pix1 = 300 First pixel in the dispersion axis
pix2 = 500 Second pixel in the dispersion axis
bundle = 2 SB1(1), SB2(2), SB3(3)
bias = 1000 BIAS
outimage = "M32_300_500" Outimage
(mode = "q")

Extraction of a particular spectrum
This is done with the task int_nspec. In the example below, the spectrum #25 of "M32center" will be stored in the file "M32_25".

The first step of the int_nspec task is the definition, tracing, and extraction of the "referenceflat" (see the last section).

Secondly, the apertures are defined, traced and extracted for the object image (see the last section).

After that, a calibrated (or non-calibrated) spectrum of the selected fiber is showed on display. The calibration is done acoording to the parameters of the image header.

Note that an estimation of the BIAS is required.

PACKAGE= integral
image = "M32center" Object image
reference = "referenceflat" Flat image
fibre_n = 25 Number of fibre
bundle = 2 SB1(1), SB2(2), SB3(3)
bias = 1000 BIAS
spectrum = "M32_25" Output image of the spectrum_n
calibra = yes Calibrate the spectrum (yes/no)?
(mode = "q")

next up previous contents
Next: Data Reduction Guide Up: OBSERVING PROCEDURES Previous: Controlling INTEGRAL: A Glossary

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Wed Feb 11 16:14:30 GMT 1998