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The R,I photometric observations of SBS 0335-052W were obtained occasionally
during the study of SBS 0335-052 with the 3.5m telescope in
Calar Alto on 1991 October 6.
The CCD camera was installed at prime focus of the 3.5m telescope. At f/3.5,
with the GEC CCD 1152770 pixels, (22.5 pixel-1),
the field of view is 73
49.
Two exposures of 600 s and 900 s were taken in R and I, respectively. Two clusters,
M92 and NGC 7790 were observed as photometric standards. The photometric
calibration was made using the data of Christian et al. (1985).
The observations were done under photometric conditions with a
seeing of FWHM = 144
011
and 122
002 in R and I respectively.
Airmasses were 1.45 for R and 1.46 for I.
All data reduction was done with MIDAS7. The frames were corrected for bias, dark, flat field and, additionally, in the I passband, for fringe-pattern. Unfortunately, the fringe-pattern correction was not very good and there was some residual structure in both the horizontal and vertical directions as result of additional noise in the CCD readout. This structure was corrected by applying median filters separately in X- and Y-directions.
Aperture photometry was performed on the standard star observations using
MAGNITUDE/CIRCLE task with the same aperture for all stars. The standard star
measurements were used for the determination of the magnitude zero points and the
transformation of the instrumental CCD magnitudes into the international RI system.
For the standards stars, the comparison of the CCD magnitudes with the catalogue
magnitudes shows a scatter of = 0.08 mag for R and
= 0.12 mag for I.
No color term has been included in the transformation, because tests showed
that no significant color term exist.
For photometry of extended objects, we used the package SURFPHOT as well as dedicated
software for adaptive filtering developed at the Astrophysical Institute
of Potsdam (Lorenz et al. 1993).
The adaptive filter allows one to reduce pixel noise by 3-4 times without loss
of spatial resolution of bright cores of stars and galaxies and to retain
the object's total flux as well. The smoothing scale of the adaptive filter was
1111 pixels.
Before applying an adaptive filter a special mask was built,
where all bright stars and galaxies were masked out. Such a mask is
necessary for proper determination of noise statistics used by
the filter.
The code of fitting sky background from the package for adaptive filtration was used.
It constructs background within masked regions with no use of any polinomial approximation.
Instead the so called algorithm of 'stretched skin' is used, which iterativly fill
background inside the mask by interpolation of that from outside the mask.
Total magnitudes are R = 19.03
0.09 mag and I = 19.08
0.14 mag for
SBS 0335-052W and R = 16.57
0.08 mag and I = 16.92
0.12 mag
for SBS 0335-052. The total magnitude I for SBS 0335-052
is in a good agreement with total I = 16.88 mag from TIL97.
Elliptical fitting was performed with FIT/ELL3 in SURFPHOT
package where isophotes of galaxies were fitted by ellipses and
the deviations were analysed by means of Fourier techniques
as is described by Bender & Moellenhoff (1987).
To construct a surface brightness profile we used the effective radius as the
geometrical average, Req=.
The brightness profile was decomposed into two components: with gaussian distribution
in the central part and exponential disk.
For this FIT package was used. Weights in fitting procedure were accepted as proportional to
1/
, where
is the instrumental accuracy of surface brightness profile.
The R images, isophotes and profiles with their decomposition
for SBS 0335-052 and SBS 0335-052W are shown in Fig.4.
The error bars for surface brightness profiles in both R and I are less than symbol
size. Therefore they are shown only on the (R-I) profiles.
The error bar for the first point shows the accuracy of the transformation to
the standard system.
The error bars for the rest points show the instrumental accuracy
of the color and take into account the detector gain and
photon statistics for each frame.
The best linear fits to the outer parts of the R surface brightness distributions are
given by:
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