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Astron. Astrophys. 327, 562-568 (1997)

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2. Observations and reductions

We obtained long V and I exposures ([FORMULA]  s in each color) with the 100´ DuPont telescope at Las Campanas Observatory, Chile, in the nights of 26-29 September, 1994. We used a Tektronix [FORMULA] pixel chip, with a pixel size of [FORMULA] m or [FORMULA] at the sky, corresponding to a total field of view of [FORMULA]. The data reduction and calibration is described in Kissler-Patig et al. (1996). The seeing of [FORMULA], measured by the FWHM of stellar images, corresponds to a linear diameter at the Fornax distance of about 72 parsec, which sets our resolution limit (e.g. globular clusters would appear as point sources).

The B exposures ([FORMULA]  s) were obtained with the 40´ Swope telescope at Las Campanas Observatory, Chile, in the night of 6/7 December, 1996. We used a SITe #1 [FORMULA] pixel chip, with a pixel scale of [FORMULA] at the sky. The seeing was [FORMULA].

The B, V, and I magnitudes of point sources inside NGC 1427A and in its surroundings were derived in the following way: first, we subtracted all objects from the images which were found and fitted with Daophot II (Stetson 1987, 1992). On this cleaned image we replaced all extended objects by values that were interpolated from the surrounding sky or the unresolved stellar component of NGC 1427A. We then smoothed these images by a [FORMULA] pixel median filter and finally subtracted the results from the original images. The final photometry was done with Daophot II on these images. The colors of all objects were measured on the same images by aperture photometry assuming a constant background of the sky. We used a circular aperture of [FORMULA].

The H [FORMULA] and R exposures were obtained at Cerro Tololo with the 0.9m telescope in the night of 1/2 December, 1995. We exposed [FORMULA]  s in H [FORMULA] and 600 s in R. The seeing was about [FORMULA]. The calibration was done by using Landolt (1992) fields.

We retrieved HST WFPC2 images of NGC 1427A in the F606W filter with exposure time of [FORMULA]  s from the STScI data archive. The effective resolution is [FORMULA], or about 15 pc in Fornax distance. Since the exposure is not deep, we used it only to check for multiplicity of the brightest point sources on the ground-based images where we had overlap.

X-ray observations of NGC 1427A were retrieved from the High Energy Astrophysics Science Archive Research Center (HEASARC) at Goddard Space Flight Center of NASA. The ROSAT PSPC pointing RP600043 is centered on NGC 1399. This pointing also includes NGC 1427A inside the field of view. An X-ray source is clearly present at the position of NGC 1427A. Unfortunately NGC 1427A is located near the window support structure of the telescope, just outside the central 40´ field of view. Therefore the spatial structure of this source is dominated by the point spread function and the rapid drop of sensitivity to the window support structure.

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© European Southern Observatory (ESO) 1997

Online publication: April 6, 1998