Discontinuities in the wavefront phase or amplitude affect curvature sensor (CS) response. These discontinuities may be the result of an improper alignment of the elements of a segmented mirror in either piston or tip-tilt. We describe the CS response with an analytical approach based on the Fresnel approximation of the diffracted field and show

Not Available

Comet 21P/Giacobini-Zinner was observed from Nov. 8 to Dec. 10, 1998. Pre- and post-perihelion CCD images of the gas (CN, C2) and dust (green and red continua) coma were obtained with the 82 cm IAC-80 telescope at Teide Observatory (Canary Islands, Spain). For vp =0.85 rH-0.5 and vd = 1.19 km s-1 (i.e. characteristic of HCN being the CN parent

It is foreseen that Extremly large telescope (ELT) will include Adaptive Optics Systems to provide diffraction-limited images in the near infrared. The preliminary atmospheric turbulence properties which affects laser guide star (LGS) generation are presented here. The results of modern model developed in optical communication through atmosphere is

Updated solar frequency splitting measurements suggest a slight decrease of the rotation rate below 0.25 Rsolar and, albeit preliminary, rule out a core rotating faster than the upper radiative zone. The estimates of the rotation rate of the deep solar layers are based on new rotational frequency splittings computed using data from the GOLF and MDI

We have inverted most of the available rotational frequency splittings at intermediate degrees. Namely, LOWL data from 1994 to 2000, GONG data from 1995 to 2001, and, MDI data from 1996 to 2002. Our purpose was to look for any temporal variation of the tachocline and its relation to the solar activity cycle. However, we did not find any significant