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Дата изменения: Sat Mar 11 12:16:53 2000
Дата индексирования: Sat Sep 11 20:55:15 2010
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Reduction of photometric data

All primary data reduction was done with MIDAS. The frames were corrected for bias, dark, and flat field in the same way as for reduction of the 2D frames of NOT long-slit spectra. Aperture photometry was performed on the standard star frames using the MAGNITUDE/CIRCLE task, with the same aperture for all stars. The instrumental magnitudes were transformed to the standard photometric system magnitudes via secondary local standards, calibrated with the 1m telescope of SAO. The final zero-point uncertainties of the transformation were $\sigma_{B}$ = $0\fm06$ in B, $\sigma_{V}$ = $0\fm05$ in V, and $\sigma_{R}$ = $0\fm08$ in R.

For the creation of the sky background, we used the dedicated software for adaptive filtering developed at the Astrophysical Institute of Potsdam (Lorenz et al. [1993]).

The photometry of extended objects was carried out with the IRAF software package. Elliptical fitting was performed with the ELLIPSE task in the STSDAS package. To construct a surface brightness (SB) profile we used the equivalent radius as the geometrical average, R^*=$\sqrt{ab}$. The SB profiles were decomposed into two components: one with a gaussian distribution in the central part and the second being an exponential disc. The final function has the form:

$$I = I_{\rm E,0} \exp\left(-\frac{R^*}{\alpha_{\rm E}}\right) ... ...eft[-\ln 2 \left(2 \frac{R^*}{\alpha_{\rm G}}\right)^2~\right]$$ (1)

For the profile decomposition, the NFIT1D task of the STSDAS was used with weights inversely proportional to the accuracy of the surface brightness profile. The final photometric errors take into account the instrumental errors and the error of transformation to the standard photometrical system. To check correctness of disc parameters we performed separately the fitting of external part of SB profile, corresponding to the region in Fig. 5 from R^* of 3 to 6. The derived disc parameters were the same within the cited errors.

For consistency with previous works (e.g. Telles et al. [1997], Papaderos et al. [1996], [1998], Doublier et al. [1999a]) the parameters of the disc have been obtained by fitting again the SB versus the equivalent radius, but we note that the obtained values should be taken with caution, because of ellipticity variations.

  

Figure 3: H I 21 cm profile of HS 0822+3542.