How important is an independent diameter measurement for the determination of stellar parameters of solar-type stars? When coupled with seismic observables, how well can we determine the stellar mass? If we can determine the radius of the star to between 1% and 4%, how does this affect the theoretical uncertainties? Interferometry can provide an

We present new echelle spectrophotometry of the Galactic H II regions M8 and M17. The data have been taken with the VLT UVES echelle spectrograph in the 3100 to 10400 Å range. We have measured the intensities of 375 and 260 emission lines in M8 and M17 respectively, increasing significatively the number of emission lines measured in previous

We present surface photometry and stellar kinematics of NGC 4431, a barred dwarf galaxy in the Virgo Cluster undergoing a tidal interaction with one of its neighbors, NGC 4436. We measured its bar pattern speed using the Tremaine-Weinberg method and derived the ratio of the corotation radius, DL, to the bar semimajor axis, aB. We found DL/aB=0.6+1

We present the first results of a large Advanced Camera for Surveys (ACS) survey of Galactic globular clusters. This Hubble Space Telescope (HST) Treasury project is designed to obtain photometry with S/N (signal-to-noise ratio) gtrsim10 for main-sequence stars with masses gtrsim0.2 Modot in a sample of globulars using the ACS Wide Field Channel

The nature of the ultra-luminous X-ray sources (ULXs) discovered in significant numbers in nearby galaxies by XMM and CXO continues to be a controversial topic. Interpreted simply as Eddington-limited accreting binaries implies compact object masses substantially in excess of those derived for typical galactic black-hole X-ray binaries. Whilst this

We propose a calibration plan for the GTC based on techniques similar to the ones used for space calibration. After studying the telescope and instrument requirements, and observing during intensive campaigns we have begun to prepare the GTC catalogue of standard stars. In this article we show the calibration strategy for the telescope and the