Examples of observations obtained with LFOSC are shown:
R band image of the field around the X-ray source RXJ1207.7+3148. The 90% SASS error circle (radius 35tex2html_wrap2797 ) is indicated. Many faint and diffuse objects, most likely distant galaxies, are visible. The brightness of the faintest visible objects is R~23. For the two brightest objects near the source position, designated by "A'' and "B'', spectra were obtained. The remaining objects are too faint for spectroscopy. Object "A'', whose spectrum is shown in the lower panel, appears to be a galaxy with R~ 20.3m and B~ 22.3m. Absorption features most likely due to MgI b and NaI D with a redshift of z~0.23 are visible. Residuals of the night sky lines are marked by "ns'', "x'' is a cosmic. Object "B'' is a 16th magnitude F-type star. This star is visually too faint to be a plausible counterpart. On the B image no object brighter than about 22tex2html_wrap_inline2703 was visible making a QSO as counterpart unlikely. The galaxy "A'' is visually too faint to be a plausible counterpart of the X-ray source . Hence, the most likely identification of this X-ray source is a distant cluster of galaxies.
R image of the X-ray source RXJ0747.3+6822. The 90% SASS error circle is indicated (radius 44" ). With two exposures spectra of all objects within 60" radius around the RASS position could be obtained. "r'' denotes reflex images of bright stars in the field. In the lower panel the spectrum of object "A'' is displayed which is the likely counterpart of the RASS source. It is a Sy 1 galaxy with V~ 18m at redshift z = 0.120.
R image of the position of the X-ray source RXJ0403.5+0837. In the the 90% SASS error circle (radius 44" ) several possible candidates for the optical counterpart are visible. The objects observed spectroscopically are designated by S1, "2'', "5'', and "8''. The bright object S1 is a 13th magnitude G to K-type star. Object #5 with V~18.4tex2html_wrap_inline2723is a QSO with Htex2html_wrap_inline2725+[OIII ] and MgIItex2html_wrap_inline2727 at redshift z = 0.589. Htex2html_wrap_inline2731 partly falls into the atmospheric band at 7600Å. Each of the two objects could be the X-ray source or at least contribute to the observed X-ray flux (see text). The remaining objects are faint stars which can be excluded for being the counterpart of the X-ray source
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