It is well known that when measuring electron densities in H II regions locally via emission line ratios the values observed are 100cm-3, but gobal values obtained via emission measure using surface brightness as the observed parameter are ~1cm-3. This difference is attributable to density fluctuations,and traditional models for these is the `

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We have studied here for the first time the use of the log(H 0/[N 0]), log (H 0/[S 0]) diagnostic diagram for determining the metallicities and ionization parameters of the H 0 regions in the Local Group. An important advantage of using these lines is their proximity in wavelength, which both simplifies the observations and makes the de-reddening

We present here a study of the Hα equivalent widths of the flocculent galaxy NGC 4395 and the grand-design galaxy NGC 5457. A difference between the mean values of the Hα equivalent widths for the two galaxies has been found. Several hypotheses are presented in order to explain this difference: differences in age, metallicity, star formation rate

The need of the GTC for acquisition cameras, wavefront sensors and scientific instrumentation operating in the optical wavelength range has led to the acquisition of various CCDs and CCD controllers. Due to stringent science, mechanical and ambient requirements the initial idea to employ a general purpose controller had been dropped in favor of two

We describe an ongoing effort to validate the estimated atmospheric parameters (Teff, log g, [Fe/H]) obtained from SDSS spectroscopy (R = 2000) and ugriz photometry, which are being employed for both the previous SDSS-I and the ongoing SEGUE surveys. The spectroscopic pipeline makes use of a number of methods for the estimation of each parameter