Resumen
We present preliminary OSIRIS Hα, [NII] and [SII] images and line-ratios on the large-scale shock (about 40 kpc long) discovered in the most popular compact group of galaxies: the Stephan's Quintet. The images were obtained by the instrument OSIRIS attached to the GTC. In this work we study only the central region of the shock and show that the shocked region is formed of bright clumps embedded in faint, diffuse gas. We confirm that the shocked gas has high (larger than one) [NII]/Hα and [SII]/Hα line-ratios, characteristic of interstellar radiative shocks and we are able of estimating electron densities from the [SII] 6717/6731 line-ratio.
