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Astron. Astrophys. 325, 135-143 (1997)

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2. Observations

Observations were made on the nights of September 8 and 9, 1994 with the 1.3 m telescope at Skinakas Observatory in Crete. The telescope is an [FORMULA] Ritchey-Cretien. A CCD camera with a Thomson chip of [FORMULA] pixels of size 19 µm each was used for the observations. This arrangement corresponds to 0.39 arcsec/pixel and a field of view of approximately [FORMULA]. Assuming a distance of 63 Mpc for UGC 2048 (Gourgoulhon et al. 1992), the pixel size corresponds to 0.12 kpc. The chip was run with a gain of 3.33 [FORMULA] /ADU and showed a readout noise of [FORMULA]. Exposures were made through B, V, I broad band filters. The B and V passbands are comparable to those of Johnson's photometric system, while the I passband is comparable to that of Cousin's photometric system. The effective wavelength of the system (filter and camera) in each passband is [FORMULA] m, [FORMULA] m and [FORMULA] m for the B, V, I bands respectively. During each night, three Landolt standard fields were observed at different airmasses. Each field had four to six standard stars. In this way, zero point, atmospheric extinction coefficient and colour terms could be obtained for the specific nights. Twilight flatfield frames were also taken in order to correct for pixel to pixel variation. The total integration time was 120 min in B, 50 min in V and 20 min in I. The seeing was [FORMULA] and [FORMULA] respectively for the two nights.

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© European Southern Observatory (ESO) 1997

Online publication: May 5, 1998