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Astron. Astrophys. 333, 803-808 (1998)

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2. Observation and reduction

Broad band Johnson B, V and Cousins R and I images of NGC 2076 were taken at the Prime focus of the 2.3m Vainu Bappu telescope of the Vainu Bappu Observatory, Kavalur, India during March, 1996, as a part of a CCD imaging programme on a sample of early-type galaxies. The observations were carried out using a 1024 [FORMULA] 1024 chip with pixel size 24 µm square pixels in direct imaging mode. This gives a scale of [FORMULA] per pixel and a total field of [FORMULA]. We obtained one frame each in B, V, R and I filters, with exposure times 40, 30, 15 and 15 minutes respectively, to obtain good signal-to-noise ratio in all the filters. Observations were taken under photometric conditions and seeing was in the range [FORMULA] - [FORMULA] (FWHM). Several sky flats in each filter and bias frames were taken for pre-processing of the CCD data.

Cleaning of these images was done using standard tasks within IRAF 1. Galaxy frames in different filters were aligned to an accuracy better than 0.1 pixel by translation. These frames were convolved with gaussian to make seeing of the best frame comparable to the worst one. The field of view of our telescope-detector combination was large [FORMULA] [FORMULA] x [FORMULA], so we could easily select regions far off from the galaxy and not affected by the foreground stars, to get the sky background.

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© European Southern Observatory (ESO) 1998

Online publication: April 28, 1998