During the GTC integration phase, the Commissioning Instrument (CI) will be a diagnostic tool for performance verification. The CI features four operation modes-imaging, pupil imaging, Curvature WFS, and high resolution Shack-Hartmann WFS. After the GTC Commissioning we also plan to install a Pyramid WFS. This instrument can therefore serve as a

On two occasions, we obtained nearly simultaneous ~=4 ks snapshot observations of the Galactic black hole and microquasar XTE J1550-564 with Chandra and RXTE near the peak of its 2000 May outburst. The low-energy sensitivity of Chandra and the resolution of the High Energy Transmission Grating Spectrometer (HETGS), coupled with the broad energy

Broad-band images have been obtained at the extremes of the continuum absorption coefficient of the solar atmosphere, at lambda 0.8 mu m and lambda 1.55 mu m. Quiet regions have been observed for different heliocentric angles. The centre-to-limb variation of granulation contrast has been computed in both wavelength ranges and a steeper decrease in

Stellar spectroscopic classification has been successfully automated by a number of groups. Automated classification and parameterization work best when applied to a homogeneous data set, and thus these techniques primarily have been developed for and applied to large surveys. While most ongoing large spectroscopic surveys target extragalactic

We compare B supergiants stellar parameters derived from analyses using plane-parallel and unified model astmospheres. Both codes are stationary, NLTE and un-blanketed, and the atomic data set is also the same for both of them. Plane-parallel model atmospheres are calculated with ALI using DETAIL/SURFACE for silicon level populations and for the

We present a way of handling and interpreting stellar proper motions, in which the idea of substituting them by great circles, proposed by Herschel in 1783, allows us to take the entire celestial sphere as a field of application, making possible the study of dense and extensive stellar zones. A suitable mathematical processing of data together with