Table information for 'cars.images'


Table Description:

Metadata for co-added CFHTLS archive images used for producing the CARS source list (cars.srccat).

This table is available for ADQL queries and through the TAP endpoint.

Resource Description: Images and data from from the CFHTLS archive research survey, a multi-band dataset spanning 37 square degrees of sky in high galactic latitudes.

For a list of all services and tables belonging to this table's resource, see Information on resource 'CARS survey data'

Citing this table

This table has an associated publication. If you use data from it, it may be appropriate to reference 2009A&A...493.1197E (ADS BibTeX entry for the publication) either in addition to or instead of the service reference.

To cite the table as such, we suggest the following BibTeX entry:

  title={{CARS} survey data},
  author={Erben, T. and Hildebrandt, H. and Lerchster, M. and Hudelot, P. and Benjamin, J. and van Waerbeke, L. and Schrabback, T. and Brimioulle, F. and Cordes, O. and Dietrich, J. P. and Holhjem, K. and Schirmer, M. and Schneider, P.},
  howpublished={{VO} resource provided by the {GAVO} Data Center}

Resource Documentation

These services deliver products from the CFHTLS-Archive-Research Survey (CARS). The survey currently offers derived products from 37 sq. degrees of the Wide part from the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS). The main documentation for the products, its creation and its content is the publication 2009A&A...493.1197E. Here, we discuss some points which are not evident from this publication.


For each 1 sq. deg. CARS pointing we currently offer the following products (we discuss them on the example of the CARS pointing W1m0p1); a typical file is named The name contains the following information:

The individual files we offer are:
object catalogue in FITS binary format; beware that they are very big and cumbersome to handle if you do not have efficient tools to work on big FITS binary tables! (typical file size per field: 0.5GB!)
An ASCII version of containing a subset of the most important catalogue quantities. This catalogue should be sufficient for most users. The main content of the catalogue can also be queried in the cat service. (typical gzipped file size per field: 20MB)

An ASCII ds9 region file containing saoimage/ds9 polygon entries (in pixel coordinates). They represent the CARS image masks described in Sect. 3.4 of 2009A&A...493.1197E. Polygons originating from different masking procedures are encoded with different colours (look at expressions such as '# color=yellow' at the end of each line). We offer this file so that interested users can construct own masks containing only parts of our global MASK key. (typical gzipped file size per field: 1MB)

The colour coding in these files is as follows:

  • yellow: masks from our object density analysis and stars identified in the USNO-A2 catalogue
  • green: stars identified in the GSC1 and GSC2 cataogues
  • magenta: masks around extended haloes of bright stars
  • red: masks from our asteroid track analysis


low resolution true colour i', r' and g' JPG image of the CARS field. These images allow a quick look at the data but they are probably not suitable for high-quality poster print-outs. (typical file size per field: 10MB)

low resolution JPG image showing object positions and object masks overlayed on the i'-band image. It allows a quick-look at field-layout and object positions. (typical file size per field: 3MB)

The colour coding in this is:

  • green: areas excluded from scientific analysis by our MASK key
  • yellow: stellar sources (SExtractor CLASS_STAR >=0.95)
  • red: galaxies with high-confidence photo-z estimates: (SExtractor CLASS_STAR < 0.95; reliable object photometry in five bands; BPZ ODDS quality parameter > 0.9); see also Sect. 4 of 2009A&A...493.1197E
  • blue: all other galaxies (SExtractor CLASS_STAR < 0.95)


See 2009A&A...493.1197E, in particular Sect. 4, and the SExtractor Users manual for a description of most catalogue entries. Also see the table notes.


CARS coverage


Sorted by DB column index. [Sort alphabetically]

NameTable Head DescriptionUnitUCD
accref Product key Access key for the data N/A meta.ref.url
owner Owner Owner of the data N/A N/A
embargo Embargo ends Date the data will become/became public a N/A
mime Type MIME type of the file served N/A meta.code.mime
accsize File size Size of the data in bytes byte VOX:Image_FileSize
centerAlpha Ctr. RA Approximate center of image, RA deg pos.eq.ra
centerDelta Ctr. Dec Approximate center of image, Dec deg pos.eq.dec
imageTitle Title Synthetic name of the image N/A meta.title
instId Instrument Identifier of the originating instrument N/A;instr
dateObs Obs. date Epoch at midpoint of observation d time;obs.exposure
nAxes #axes Number of axes in data N/A pos.wcs.naxes
pixelSize Axes Lengths Number of pixels along each of the axes pixel pos.wcs.naxis
pixelScale Scales The pixel scale on each image axis deg/pixel pos.wcs.scale
refFrame Ref. Frame Coordinate system reference frame N/A pos.frame
wcs_equinox Equinox Equinox of the given coordinates yr time.equinox
wcs_projection Proj. FITS WCS projection type N/A pos.wcs.ctype
wcs_refPixel Ref. pixel WCS reference pixel pixel pos.wcs.crpix
wcs_refValues Ref. values World coordinates at WCS reference pixel deg pos.wcs.crval
wcs_cdmatrix CD matrix FITS WCS CDij matrix deg/pixel pos.wcs.cdmatrix
bandpassId Bandpass Freeform name of the bandpass used N/A instr.bandpass
bandpassUnit Bandpass unit Unit of bandpass specifications (always m). N/A N/A
bandpassRefval Band Ref. Characteristic quantity for the bandpass of the image m instr.bandpass;stat.median
bandpassHi Band upper Upper limit of the bandpass (in BandPass_Unit units) m instr.bandpass;stat.max
bandpassLo Band lower Lower limit of the bandpass (in BandPass_Unit units) m instr.bandpass;stat.min
pixflags P. Flags Flags specifying the processing done (C-original; F-resampled; Z-fluxes valid; X-not resampled; V-for display only N/A meta.code
coverage Coverage Field covered by the image deg N/A
fieldKey Field CARS field designation N/A
fieldBandKey Field/Band CARS field designation plus band N/A
ncombine Combined Number of individual frames in this stack N/A meta.number
texptime Tot. Exposure Total Exposure Time s time.duration;obs.exposure
magzp Mag. ZP AB Magnitude Zeropoint mag phot.mag;arith.zp
magzperr Err. Mag. ZP Estimated Magnitude Zeropoint Error mag stat.error;phot.mag;arith.zp
seeing Seeing Measured image seeing arcsec instr.obsty.seeing
seeingerr Err. Seeing Measured image Seeing error arcsec stat.error;instr.obsty.seeing

Columns that are parts of indices are marked like this.


The following services may use the data contained in this table:


VO nerds may sometimes need VOResource XML for this table.

Copyright and such:

If you use the CARS products for your own research, please give proper acknowledgment to CADC, the CFHTLS project and the publication 2009A&A...493.1197E