II. Project definition and preparation:

The COMBO-17 project was started after three inspiring prerequisites came together: The CADIS survey showed that classification and redshift estimation in surveys with medium-band filter sets are a powerful and accurate tool for studies on the evolution of galaxies and quasars over most of the time the universe existed. The survey strategy is capable of replacing time-consuming spectroscopy as the main tool for classification and redshift measurements. The filter set used in COMBO-17 was shown by extensive simulations and analytic considerations to deliver the best performance among a range of possible filter sets considered. The Wide Field Imager WFI@2.2 was commissioned in 1999 and contained by design a set of filters well suited for medium-band surveys. Collaborations within and outside of MPIA helped to establish the final survey strategy considered optimal for research in evolution of galaxies and quasars as well as weak lensing.

III. Development of reduction pipeline, calibration and classification:

A reduction pipeline for dithered WFI survey images has been developed for the MIDAS environment with participation by S. Dye, M. Kleinheinrich, K. Meisenheimer and C. Wolf in the years 1999 and 2000. This pipeline is installed as a MIDAS context file named WFI and makes use of the other context packages MPIAPHOT and CADIS, which were developed by the CADIS team from 1997 to 1999. All elements of the pipeline have been tested and work as desired. The pipeline consists of two main parts: The first part is used for basic reduction from raw images located on DAT tapes to sumframes and flatfield- and cosmic corrected individual frames. It is also used for running SExtractor with a recommended setup on the sumframes to get object tables. The second part works fully automatic on a set of existing and reduced frames to generate a final calibrated object table with photometry on all available filters. After quality checks on photometry and calibration, a multi-color classification and redshift estimation can be applied to the catalog. As an input the pipeline uses a bad column+bad pixel mask for the WFI, a SExtractor setup file, tertiary standard star spectra in proper format, efficiency curves of all filter used in proper format and color template libraries of the used filter system in proper format.

IV. Observations:

	All observations were performed with the Wide-Field Imager at the MPG/ESO 2.2-m telescope at La Silla observatory, Chile, and finished by January 2001. A total of 48.5 nights have been used for COMBO observations, with 38 usably clear nights in seeing below 1.4 arcsec. A dither pattern with 2'x 3' size is used for cosmic correction, compensation of CCD cosmetics and for the construction of science flats. The latter are needed any time in the far-red filters and for all filters observed before Feb, 4, 2000 due to scattered light in the flatfields.

	run	code	date period	nights	turnout	fields	observers
	Feb 99	A	11.02.-22.02.1999	9	~75%	A901, S11	CW, RW
	Jun 99	B	03.06.-17.06.1999	2	~90%	S11	JE, SW
	Aug 99	C	04.08.-08.08.1999	2.5	~90%	SGP	JG
	Oct 99	D	07.10.-22.10.1999	12	~50%	SGP, FDF, AXAF	CW, TK
	Jan 00	E	28.01.-11.02.2000	15	~90%	AXAF, A901, S11	CW, MK, KM
	Oct 00	F	00.09.-00.09.2000	5	~90%	SGP, FDF, AXAF	MK
	Jan 01	G	19.01.-20.01.2001	2	~90%	AXAF, A901, S11	CW, KM
	May 02	H	00.05.-30.05.2002	1	~90%	S11	service
	Aug 02	I	16.08.-13.09.2002			FDF, A226	service
	Oct 02	O	Periode P69			SGP	service
	Aug 03	J	08.08.-28.08.2003			AXAF, A226	service
	Dec 03	K	02.12.-20.12.2003			SGP, A226	service
	Dec 04	L	01.12.-19.12.2004			SGP, A226	service
	Aug 05	M	08.08.-12.08.2005			SGP, A226	service
	Dec 05	N	20.11.-04.12.2005			SGP, A226	service
	Nov 06	P	13.11.-28.11.2007	2	~95%	SGP, A226	CW, MZ (MPIA service)

V. Data reduction:

Data reduction is now complete and has been performed with MIDAS image processing software on SUN Enterprise workstations. Many additional routines are used and installed as context environments CADIS, MPIAPHOT and WFI. Disk space includes a Terabyte raid system, where individual frames needed for accurate photometric error calculation can reside on disk. For details on the reduction procedure we refer to our WFI processing cookbook. Data quality control includes inspection of flatfields, success of cosmic correction, depth and background properties of the sum images, precision checks for the coordinate projection onto all individual frames, and finally checking error distributions and calibrations in the final flux table of the object catalog.

VI. Results:

	see Results & Papers page

Back to COMBO-17 index page