The aim of a data reduction process is to minimize the influence of data acquisition imperfections on the estimation of the desired astronomical quantity. For this purpose, one must perform appropriate manipulations with data and calibration frames. In addition, random-error frames (computed from first principles: expected statistical distribution

Phase and gain relations between low-degree acoustic modes measured as intensity and velocity fluctuations have been carried out using various instruments and techniques. The helioseismic instrument aboard the Solar and Heliospheric Observatory (SOHO) satellite provides an opportunity to observe solar oscillations in intensity and velocity under

OSIRIS (Optical System for Imaging and low/intermediate-Resolution Integrated Spectroscopy) is an instrument designed to obtain images and low resolution spectra of astronomical objects in the optical domain (from 365 through 1000nm). It will be installed on Day One (middle of 2004) in the Nasmyth focus of the 10-meter Spanish GTC Telescope. This

We present high-resolution observations of the giant extragalactic H II regions NGC 604, NGC 2363, NGC 5461, and NGC 5471, based on observations taken with the ISIS spectrograph on the William Herschel Telescope. We have detected, for the first time, C II and O II recombination lines in these objects. We find that recombination lines give larger C+

Almost every star in our galaxy will eventually become a white dwarf. Since they are relatively simple compared to main-sequence stars, white dwarfs provide one of the best opportunities for learning about stellar structure and evolution. Studies of pulsating white dwarfs give us the opportunity to learn about their internal composition and

We analyze the old stellar population in the near infrared data around the Galactic plane of the 2MASS survey.