XSTARFINDER



  1) GENERAL DESCRIPTION.

  XStarFinder is a general purpose astrometry and photometry
  toolkit for crowded stellar fields analysis.
  It has been designed for well-sampled high and low Strehl
  images. The current version considers the PSF constant over
  the field of view; a method to handle anisoplanatic effects
  in wide-field Adaptive Optics observations is under
  development.



  2) MAIN MENU DESCRIPTION.

  The controls in the main menu are:

  'Image' pull-down menu:
      Load image from FITS file, display it and perform basic
      operations (compute standard deviation of gaussian noise,
      repair bad pixels, select reference sources by mouse click).
      Save by-products of the analysis (e.g. image after repair
      of saturated stars, synthetic field, background estimate,
      etc.).

  'PSF' pull-down menu:
      Load PSF from FITS file or extract it directly from the
      image. The PSF extraction task allows the user to repair
      the saturated stars in the input image.
      The 'PSF' pull-down menu includes tasks for basic post-
      processing of the extracted PSF (e.g. support masking,
      halo smoothing, normalization) and allows one to save
      the retrieved estimate of the PSF.

  'Astrometry and Photometry' button:
      Detect stars in the input image, performing astrometry and
      photometry. The PSF, either load from a file or extracted
      from the image, is used as a rigid template which may be
      shifted and scaled to match other objects in the field.
      The list of detected stars can be saved to an ASCII file.

  'Compare Lists' button:
      Compare two data sets representing the results obtained
      on different images of the same field (e.g. in different
      filters) and create a simple color-magnitude diagram.
      The data sets are supposed to be reciprocally translated
      and rotated. The plotted diagram can be saved as
      PostScript file.

  'Display' pull-down menu:
      Define display options (intensity range, stretch, chopping
      threshold, color table) for the currently displayed image.

  'Session' pull-down menu:
      Save current session or restore a previously saved one.

  'Help' button:
      Display this help file. Notice that every secondary widget
      application is provided with its own help page.

  'Quit' button:
      Exit XStarFinder.



  3) NOTES ON VARIABLES.

  XStarFinder is a compound application. The main widget which
  appears on the screen (called XStarFinder) is nothing more than
  an interface allowing the user to call different widget-based
  applications, in order to perform various operations on the
  stellar field image.
  The main widget defines a memory area to store some 'global'
  variables, namely
  - image: the stellar field
  - PSF: array containing an image of the Point Spread Function
  - noise: array, with the same size as the image, containing the
       noise standard deviation for each image pixel
  - background: array, with the same size as the image, with an
       estimate of the background emission. Available after PSF
       extraction or stellar field analysis
  - detected stars: synthetic image, containing one replica of the
       PSF for each detected star in the field. Available after
       stars detection
  - synthetic field: sum of background array and detected stars
  - list of detected stars: positions, fluxes, formal errors and
       correlation coefficients. Available after stars detection
  - other data and parameters.
  The global variables are maintained and modified in the course
  of the current session. As one of these variables is processed
  by some application, its previous value is overwritten: if the
  user wishes to keep track of the values assumed by the variable
  in the course of the session, he/she should save the variable
  itself or the entire session whenever necessary.
  All the global data are basically divided into two groups:
  those associated to the image (image, background, noise array,
  stellar field model, list of detected stars, ...) and those
  associated to the PSF (PSF array, coordinates of stars selected
  by the user to form the PSF, ...). Whenever the user loads a new
  image or a new PSF, all the associated data are erased, to avoid
  'mixing' different data. The only exception is represented by
  the default parameters of the secondary widgets applications
  (see below): in this case the user selected parameters are saved.
  Every secondary widget application has a set of default
  parameters, which can be modified interactively by the user.
  The user-defined values become the new default values of the
  widget's set of parameters until the user quits XStarFinder
  without saving the current session. This feature may help the
  user to analyze two images of the same field. Of course, if the
  observations were taken at different wavelengths, all the
  'structural' parameters (e.g. those related to the PSF FWHM,
  as the box size for PSF extraction) must be scaled properly.
  Nevertheless, saving the user-defined values of the widgets'
  parameters might be tricky in some situations, for instance
  when two images of different targets and/or in different
  observing conditions are analyzed in sequence. In these cases
  it is recommended to close the current XStarFinder session
  and open a new one, in order to restore the default values of
  the parameters.

 

  4) NOTES ON INPUT/OUTPUT.

  XStarFinder can load/save images from/to FITS files. Every
  output FITS file has the same header as the corresponding input
  file. A minimal default header is written when the saved item
  has no corresponding input (e.g. the PSF when it is extracted
  from the stellar field).
  It is strongly recommended to avoid overwriting existing FITS
  files, to avoid losing important header information.