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Subsections

Appendix A: Spectral observations and results

A.1 Observations and reduction

All observations have been conducted with the SAO RAS 6m telescope during the period 1996-2000. Besides candidate companion galaxies, three SBS BCGs were also observed. For one of them (SBS 1413+495) the redshift was unknown before, and for two others we tried to improve the accuracy of redshifts to make more confident our search for companions. This optical redshift for SBS 1413+495 was later confirmed and its precision was improved using HI data by Thuan et al. (1999). Candidate neighbours for two additional BCGs not entering into the sample of 86 BCGs were also observed, and appeared to be real companions (SBS 0916+542 and 1120+586). Observational results on these two new galaxies are given as well in Table A.1.

Three set-ups were used for the observations:

1.
The first one was based on the spectrograph SP-124 in the Nasmyth-1 focus with a Photometrics 1K$\times$1K CCD detector (PM1024) with $24\times24~\mu$m pixel size. We used the gratings either with 300 grooves/mm or with 600 grooves/mm. A long slit of 1 $.\!\!^{\prime\prime}$5-3 $.\!\!^{\prime\prime}$0$\times$40 $^{\prime\prime}$ was used. The scale along the slit was 0.4 $^{\prime\prime}$/pixel or 0.5 $\hbox{$^{\prime\prime}$ }$/pixel. Various spectral set-ups were used with dispersions from 2.4 to 5.5 Å/pixel and a wavelength coverage of 4500-7000 Å. More details on this set-up observations are given, e.g., in Pustilnik et al. (1999);

2.
The second set-up was based on the spectrograph SP-124 in Nasmyth-1 focus with a Russian ISD017A 1040$\times$1160 CCD detector with $16\times16~\mu$m pixel size and quantum efficiency ${\approx}50\%$ near ${\sim}6000$ Å. This set-up was used only during 1 run in summer 1998, and few spectra were obtained. The same gratings and long slit were used as for the previous set-up;

3.
The most recent observations were conducted with the spectrograph LSS (Afanasiev et al. 1995) in the prime focus and PM1024 CCD (as at first set-up) as a detector. Most of the long-slit spectra (1 $.\!\!^{\prime\prime}$2-2 $.\!\!^{\prime\prime}$0$\times$180 $^{\prime\prime}$) were obtained with the grating of 325 grooves/mm, giving a dispersion of 4.6 Å/pixel (the spectral resolution 12-15 Å (FWHM)) and the spectral range of 3600-8000 Å. The scale along the slit was 0.39 $^{\prime\prime}$/pixel.
All observations were followed by recording the reference spectrum of a He-Ne-Ar lamp. Bias, dark noise and flat field were obtained every night. Observations of the spectrophotometrical standards from Bohlin (1996) were used to derive the sensitivity curve of the overall system. All observations and data acquisition were conducted using the NICE software package by Kniazev & Shergin (1995) in the MIDAS[*] environment.

Since these observations were performed mainly as a back-up program, in most of the cases the conditions were not photometric. Our main goal was to get radial velocity of the studied candidates. Therefore we discuss only this parameter.

Reduction was done as follows. Cosmic ray hits removal was done in MIDAS. The standard procedures of debiasing, flatfielding, wavelength and flux calibration were done in IRAF[*]. Standard routines IDENTIFY, REIDENTIFY, FITCOORD, TRANSFORM were used to do the wavelength calibration and the correction for distortion and tilt for each frame. Then the one-dimensional spectra were extracted from each frame using the APALL routine without weighting. To derive the instrumental response function, we fitted the observed spectral energy distribution of the standard stars with a high-order polynomial.

Final measurements of the line intensities and positions and radial velocities were done in MIDAS. To improve the accuracy of the redshift determination, and further, to reduce possible small systematic shifts in the zero point of the wavelength calibration, we additionally checked the wavelengths of the night sky emission lines on the 2D spectra at the position of the object spectrum.

A.2 Results of spectroscopy

The objects observed are listed in Table A.1 containing the following information:
Column 1: The object's IAU-type name.
Column 2: Right ascension (RA) for equinox B1950.
Column 3: Declination for equinox B1950.
Column 4: Apparent B-magnitude from APM database (Irwin 1998) which was recalculated to standard CCD B-magnitude using the calibration suggested by Kniazev et al. (2001b). Its rms uncertainty is 0 $.\!\!^{\rm m}$45 over the magnitude range $B=14\hbox{$.\!\!^{\rm m}$ }0$ to $18\hbox{$.\!\!^{\rm m}$ }5$.
Column 5: Heliocentric velocity and its rms uncertainty in km s-1.
Column 6: Absolute B-magnitude calculated from the apparent B magnitude and the heliocentric velocities. No correction for galactic extinction is made because all observed objects are located at high galactic latitudes and because the corrections are significantly smaller than the uncertainties of the magnitudes.
Column 7: Preliminary spectral classification type according to the presented spectral data. BCG/H II means that the galaxy possesses a characteristic H II-region spectrum and a low enough luminosity ( $M_B \geq -20$). SBN are spiral galaxies of lower excitation with the central SF burst and the corresponding position in the line ratio diagrams, as discussed, e.g., in Ugryumov et al. (1999). Seyfert galaxies are separated mainly on the diagnostic diagrams as AGN. The criterion of broad lines was also used for the Sy classification. The ELG type means that an object has emission lines but is difficult to be classified using the existing data. ABS means a galaxy with the detected and identified absorption lines.
Column 8: One or more alternative names according to the information from NED.
Column 9: The list of spectral lines, well detected in the object spectrum and used for classification and/or redshift measurement.

All observed spectra are shown in Figs. A.1-A.3.

Acknowledgements

We are pleased to thank T. Kniazeva for the help in the reduction of observational data and D. Makarov for consultations. Our thanks to K. Noeske for sending us his and co-authors' article prior publication, and to J. Schombert, who kindly provided us with some unpublished data on the LSB galaxy sample. The authors thank the anonymous referee for useful suggestions. We acknowledge the partial support from Russian state program ``Astronomy'' and Center of Cosmoparticle Physics "Cosmion". This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. The use of the Digitized Sky Survey (DSS-II) and APM Database is gratefully acknowledged.


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