This tarball contains a collection of data from 6 Megacam standard star image obtained in September, 2003. There are two sets of three images, taken two weeks apart (03 Sep and 21 Sep). In each set, there is one each of g', r', and i' images, all short exposures of 3.0 seconds. This dataset makes a useful demonstration of the DVO system.

The tarball contains 6 directories, one for each image. The images have been processed with the Elixir system and the photflat-corrected flat-field images for each filter, though no fringe correction has been applied. Sextractor has been run on all of the images, and only the sextractor-derived photometry is available in the tarballs. No image pixel data is kept. The directories are named after the exposure odometer numbers, eg 718688o.

Within each directory, the data is separated into a number of files for each of the 36 detector, with names created by appending the chip number to the odometer number of the image, eg 718688o00. For each detector, the directory contains:

• the Elixir processing log file: *.log
• the raw sextractor output: *.sx
• the photometry data in Elixir cmp format: *.smp
• the photometry data in FITS table format: *.smf
• the photometry data with mosaic astromtry: *.xmf

The raw sextrator output consists of a fixed-format ASCII table with columns defined by the Elixir processing system. The Elixir cmp format merges the sextractor photometry table with the image header to form a pseudo-FITS table. The smf format contains essentially the same information as the smp format, but the table portion of the data is written as a FITS table in the first extension, with appropriate table description in the table header unit. The primary header of this file consists of the original image header, with the value of NAXIS set to 0. This has the effect of making the file a valid FITS file, while keeping the information of NAXIS1 and NAXIS2 (the original image dimensions), while eliminated the data taken by the image array.

Both the .smp and .smf files include the astrometric solution in the form of WCS header entries. In the case of these files, the astrometry requires a linear solution across the chip. The linear solution provides a robust solution, but results in systematic errors which are substantial, roughly 0.5-1.0 arcsec, due to the optical system distortion. A better solution can be obtained by fitting higher order polynomials. We use a two-layer solution, with one set of third-order polynomials to represent the warping of each detector, and a second third-order polynomial to represent the telescope optical distortion. The .xmf files represent the same data as the .smf files, also in the FITS table format, but with the two-layer mosaic astrometric solutions in their headers. In addition, these files require the single .phu file which represents the full-mosaic PHU and contains the top-level telescope distortion solution. It is possible to add any of these data to the DVO database using the addstar command. To add any of the .smp files, simply use the command:

addstar filename.smp

addstar -fits filename.smf

addstar -mosaic root.phu -fits filename.smf