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Reports ESO OBs and CASU reductions and plots magnitude offsets with Gaia
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- ATLAS Images
g,r,i image of NGC4039
g,r,i image of NGC289
g,r,i image of NGC7172
g,r,z image of Messier 30
g,r,i image of NGC613
g,r,i image of IC5271
g,r,i image of NGC3115
g,r,i image of NGC7268
g,r,i image of NGC1255
g,r,i image of NGC7755
g,r,i image of NGC945
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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
* ESO C grades are included, so there are repeat observations on some fields.
|No. of fields||1284||1531||1759||2015||2057|
|No. of observations*||1662||1694||1975||2506||2840|
|Approx. Area (deg2)||1200||1430||1640||1880||1920|
|Median 5σ Mag. limit (Vega)||21.08||23.20||22.56||21.58||20.32|
|Approx. offset to get to SDSS AB||+0.85||-0.1||+0.15||+0.35||+0.5|
|Median FWHM (")||1.12||1.03||0.96||0.92||0.96|
- 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.
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:
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).