VODIA (VST OmegaCAM Difference Image Analysis) is a package optimized to detect small photometric variations in crowded fields. The software is based on the DIA package (Difference Image Analysis, written by Wozniak 2000, (Acta Astron. 50, 421; see also Wozniak et al. 2002, Acta Astron. 52, 129) that makes use of the ``optimal PSF matching algorithm'' with a space-varying kernel (Alard & Lupton 1998, ApJ 503, 325; Alard 2000, A&AS 144, 363). The software includes 6 (+1) independent C programs (corresponding to 6 different steps) and does not use any external library. The inspect method makes use of a fortran program for preliminary analysis of the results. The different steps are:
VODIA has been incorporated into Astro-WISE by A. Volpicelli and F. Getman. This is done by providing a Python wrapper around the C programs which stores the input and output to the Astro-WISE database/data storage. One FORTRAN program is used only by the inspect method for preliminary analysis of the results.
The VODIA code can be found in Astro-WISE CVS at:
Extract this archive to whatever directory you like. To compile run `make'. To install: `make install'. Installation will copy binaries to user bin directory or you can copy them to system directory manually. Up to now, the code is tested for 32-bit machines only.
[import all python scripts] awe> from astro.main.VariabilityFrame import VariabilityFrame awe> from astro.external import Dia awe> from astro.main.DiaConfig import DiaMstackConfig,DiaGetpsfConfig, DiaAgaConfig,DiaGetvarConfig,DiaPhotConfig [select science frames] awe> q = ( RegriddedFrame.OBJECT.like('projectname')) &\ ( RegriddedFrame.filter.name == '#842' ) &\ ( RegriddedFrame.chip.name == 'ccd50') awe> regs = [reg for reg in q] [creates variability object] awe> v = VariabilityFrame() [put our list of images as input] awe> v.regridded_frames = regs [create the list of images to produce the reference (optional)] awe> q = ( RegriddedFrame.OBJECT.like('projectname')) & \ ( RegriddedFrame.filter.name == '#842' ) &\ ( RegriddedFrame.chip.name == 'ccd50') &\ ( RegriddedFrame.psf_radius < 0.6 ) awe> v.regridded_frames_for_reference=list(q) [run VODIA (all programs automatically)] awe> v.make() [to interactively check the results] awe> v.inspect() [Example of changing one parameter (C_MIN=detection threshold) and run again getvar and phot] awe> print v.getvar_config.C_MIN awe> v.getvar_config.C_MIN = 0.9 awe> v.make_getvar() awe> v.make_phot() [check again new results] awe> v.inspect() [storing the file with the light curves] awe> v.store() [commit the results to database] awe> v.commit()
The output consists of one ASCII file with N lightcurves (N being the number of sources analyzed).
A manual with a detailed description of VODIA is available at the Astro-WISE web site.