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Astrometric measurement techniques

Reffert, Sabine

This contribution reviews the various principles which form the basis of astrometric measurements, such as meridian circle observations, imaging techniques, scanning satellites and interferometry. Various projects which employ those techniques are described, e.g. the Multichannel Astrometric Photometer, the Fine Guidance Sensors onboard the Hubble…

Oxygen abundances derived in unevolved very metal-poor stars

Rebolo, R.; Bonifacio, P.; Molaro, P. +4 more

Oxygen abundances have been derived in a sample of very metal-poor stars from observations of the O I triplet at λλ 7771-5 Å and OH lines in the near UV. Iron abundances derived in LTE were corrected for NLTE effects following Thévenin and Idiart [ApJ 521 (1999) 753]. Furthermore, a detailed NLTE analysis of iron lines has been carried out for one…