Multiwavelength observations of the bright QSO HS 0624+6907.

We present non-simultaneous multi-wavelength observations of the bright radio-quiet QSO HS 0624+6907 (V=14.2, z=0.37) discovered by the Hamburg Survey (Groote et al. 1989). HS 0624+6907 has a particularly strong UV-soft X-ray bump which turns over already at the shortest IUE wavelengths, and it has a steep (Photon index {GAMMA}=-2.9) soft X-ray spectral slope. While the spectrum resembles in the optical UV and soft X-rays that of H 1821+643, its "twin" in the sky in brightness and redshift, its energy distribution lacks the components in the IR and at hard X-rays seen in H 1821+641. A unique feature of the emission line spectrum seen at high spectral resolution is a narrow [OIII] and H_beta_ component (FWHM=140km/s) redshifted by 360km/s relative to broad allowed lines. The QSO has been found to be slightly variable in the optical and at soft X-rays (factor 2). The host galaxy of HS 0624+6907 obeys a de Vaucouleurs-type radial brightness distribution and appears to be a giant elliptical galaxy, probably located in a cluster.