OSIRIS is the optical Day One instrument, and so far the only Spanish instrument, currently operating at the GTC. Building and testing an instrument for a 8-10m-class telescope with nonprevious commissioning in turn, has represented a truly unique experience. In this contribution, the current status, the last commissioning results and some future

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

In the last 12 years NGC 2770 hosted 2 standard supernovae (SNe) and one X-ray transient event (SN2008D) similar to a Gamma-Ray Burst (GRB). Given the close (27 Mpc) distance of NGC 2770, we could resolve with the OSIRIS tunable filter (TF) the 3 explosion sites in Hα. We also show Hα data of its satellite galaxy NGC 2770B, one of the least

The young massive cluster Cyg OB2 is the closest massive star forming region to the Sun, with hundreds of OB members, and then the best target in the Milky Way to study the feedback of massive stars on the star formation process. To study in detail the stellar population of such a unique target, Cyg OB2 has been observed with GTC/OSIRIS and Chandra

The hardware of the OSIRIS instrument is nearly complete. The instrument commissioning will continue with the validation of the remaining observing modes that are still pending. In the present contribution, the instrument status and the tasks to be tackled in the nearby future will be briefly described.

OB stars are very active actors shaping their environment and contributing to the chemical and dynamical evolution of their host galaxies. Accurate analyses of massive stars are thus a key ingredient in our interpretation of the light coming from the Milky Way and nearby galaxies. These analyses rely in the use of state-of-the-art model atmospheres