EIS Coadded Image Server: Introduction

The EIS observations consists of a sequence of 150 sec exposures. Each pointing of a patch is imaged twice (except at the edges of the patch) for a total integration time of 300 sec, using two frames shifted by half an EMMI frame both in right ascension and declination. To produce the coadded image the data is being processed by the EIS pipeline, that makes the astrometric and photometric calibration, before the background subtracted images are being coadded using the Drizzle software first developed for HST images by Fruchter and Hook, 1997.

The coadded images offered here are therefore background subtracted and because of the varying observing conditions during the EIS observing runs the noise in the coadded image will vary. The coadded images use the conical equal area (COE) projection, which is not handled by all display-tools but the ESO SkyCat Tool support this projection for display purposes.

The available images are lossy compressed using a HCOMPRESS library originally written by Richard L. White for the STScI. For the coadded sections we have used a very high compression scale of 200. In addition to the compression the images are re-sampled by a factor of 0.5 in both directions. The re-sampling code written by Nicolas Devillard is part of the eclipse library. To perform these conversions we have used a program written by Allan Brighton. In effect the size of the original images is 67 MB, whereas the compressed and re-sampled images have about 150 kB.

Of course the compression is well visible in the resulting images, but in direct comparison it is very hard to even find a single object suppressed in the compressed version.

NOTE: The images available through this service are not suited for further astronomical reduction, but are meant to serve as a source for proposal preparation and comparison with EIS catalogs or your own data sets.