Segments alignment is one of the fundamental factors affecting the shape of the PSF of a segmented mirror telescope. Tilt and piston of each segment must be very well and uniformly adjusted in relation with the rest of the segments. The Hartmann-Shack sensor is very efficient in detecting the local wavefront tilt, but the task to take measurements

This paper examines the oxygen abundance of 24 main-sequence turn-off and subgiant stars through the permitted O I triplet near $lambda$7774 {AA}. In agreement with prior investigators, we find that the O abundance from the triplet is about 0.53 dex higher than is typically found from other means such as the [O I] $lambda$6300 {AA} line or the UV

The future large telescope for the Observatorio del Roque de los Muchachos will have a 10 m diameter segmented primary made of hexagonal elements (similar to the Keck I primary). The telescope optical configuration is being selected to achieve excellent image quality and low emissivity out to the mid-IR. The design includes provision for two

We present calculations that account for the infall of matter onto the heart of a starburst, a condition thought indispensable for causing the large accumulation of matter and the large detected rates of star formation. We center our attention on the rapid evolution of the remnant generated by the collective action of strong stellar winds and

We present optical and near-infrared (NIR) surface brightness and colour profiles, in bands ranging from U to K, for the disk and bulge components of a complete sample of 30 nearby S0 to Sbc galaxies with inclinations larger than 50 deg. We describe in detail the observations and the determination of colour parameters. Calibrated monochromatic and

Mn-Cr data are reported for chondrules from the Bishunpur and Chainpur LL chondrites. It is shown that variations in Mn/Cr for these chondrules were established during condensation of solids from the solar nebula; the whole-chondrule isochrons should give an upper limit to the time of chondrule formation and an estimate of when the chondrule