SExtractor Draft - METU Astrophysics

51 What is SExtractor?SExtractor (Source-Extractor) is a program that builds a catalogue of objects from an astronomicalimage. It is particularly oriented towards reduction of large scale galaxy-survey data,but it also performs well on moderately crowded star fields. Its main features are:• Simplicity of usage and configuration.• Speed: typically 500 kpixel/s with a Pentium2@450MHz.• Ability to work with very large images (up to 65k × 65k pixels on 32bit machines, or2G × 2G pixels on 64bit machines), thanks to buffered image access.• Robust deblending of overlapping extended objects.• Real-time filtering of images to improve detectability.• Neural-Network-based star/galaxy classifier.• Flexible catalogue output of desired parameters only.• Pixel-to-pixel photometry in dual-image mode.• Handling of weight-maps and flag-maps.• Optimum handling of images with variable S/N.• Special mode for photographic scans.• Modularity of the code that enables one to implement new parameters.The purpose of SExtractor was to find a compromise between refinement in both detection andmeasurements, and computational speed.2 Installing the software2.1 Software and hardware requirementsSince the beginning in 1993, the development of SExtractor was always made on Unix systems(successively: SUN-OS, HP/UX, SUN-Solaris, Digital Unix and GNU/Linux). Successful portsby external contributors have been reported on non-Unix OSes such as AMIGA-OS, DEC-VMSand even MS-DOS Windows95 1 and NT ; ). They are however not currently supported by theauthor, and Unix remains the recommended system for running SExtractor. The software isgenerally run in (ANSI) text-mode from a shell. A window system is therefore unnecessary withpresent versions.On the hardware side, memory requirements obviously depend on the size of the images to beprocessed. But to give an idea, a typical processing of 1024 × 1024 pixel images should requireno more than 8 MB of silicon memory. For very large images, (32000 × 32000 pixels or more), aminimum of 200MB is recommended. Swap-space can of course be put to contribution, althougha strong performance hit is to be expected.1 Binaries are available on the WWW, see e.g. http://www.tass-survey.org/tass/software/software.html#sextract