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VST ATLAS DR1 Release Description

DR1 was released in November 2013

The release consists of all stacked, reduced images and associated source lists in u,g,r,i,z taken from the start of observations by the VST in August 2011 through to the end of September 2012.

Coverage maps:


Exposure time2x60sec2x50sec2x45sec2x45sec2x45sec
No. of fields12841531175920152057
No. of observations*16621694197525062840
Approx. Area (deg2)12001430164018801920
Median 5σ Mag. limit (Vega)21.0823.2022.5621.5820.32
Approx. offset to get to SDSS AB+0.85-0.1+0.15+0.35+0.5
Median FWHM (")
* ESO C grades are included, so there are repeat observations on some fields.


  • Isophotal fluxes, Kron fluxes, Petrosian fluxes and fixed aperture fluxes are provided. There are also corrections to point source total magnitudes for each aperture.
  • To convert magnitudes use -2.5*log(flux)+ MAGZPT - EXTINCT*(airmass-1) +2.5*log10(EXPTIME), where 'MAGZPT', 'EXTINCT', 'EXPTIME' are fits keywords in the headers and airmass is the mean of 'HIERARCH ESO TEL AIRM START' and 'HIERARCH ESO TEL AIRM END' (so note in particular that MAGZPT is not corrected for the airmass of the observations).
  • Fluxes are corrected for the non-uniform illumination of the flat fields
  • The pixels are NOT corrected.
  • The Kron and Petrosian magnitudes are unreliable for the brighter stellar objects. If you are interested in stars, use the point-source corrected aperture fluxes.
  • A full description of the catalogues is provided at CASU
  • The s/g Classification parameter appears to give reasonably clean samples of stars (-1), but does seems to contaminate galaxy samples (1) with fainter stars.
  • The coverage is not spatially coincident between the five bands. Only about 1000 deg2 has 5-band data.

Colour equations:

Rough colour transforms to SDSS are:

u_sdss=u_vst + 0.01(u-g)  + 0.8 
g_sdss=g_vst + 0.04(g-r)  - 0.1
r_sdss=r_vst + 0.03(g-r)  + 0.1
i_sdss=i_vst + 0.004(r-i) + 0.4
z_sdss=z_vst - 0.05(i-z)  + 0.5
The constants terms are uncertain and depend on the accuracy of the ATLAS zero-points (see below). Here is a typical comparison between SDSS and VST ATLAS for stellar objects:

Photometric uniformity:

This release has not been global calibrated and relies on the ESO nightly calibration. Observations may not be photometric. The field-by-field rms compared with external surveys is about +/-0.05 mag. However, it tends to be correlated over Concatenations, which are usually 17 tiles long in RA at the same Dec. Future releases will include global calibration based on internal overlaps between fields and/or external surveys (e.g. APASS).


Last updated May 03 2024 13:38:03.