We propose to observe six fields in the nearby dwarf spheroidal galaxy (dSph) Sculptor in order to study the stellar populations, and in particular their spatial gradients, through RR Lyrae star populations and deep color-magnitude diagrams (CMD). In addition to provide a complete census of its short-period variable stars, we will use the pulsation

A procedure to compute meteoroid spatial number densities from photographs is presented. It follows from the visual method of Koschack and Rendtel with slight changes. Some parameters are recomputed and hints are given on how to produce useful photographic observations. Finally, an analysis of the expected errors is performed.

We present a suite of cosmological radiation-hydrodynamical simulations of the assembly of galaxies driving the reionization of the intergalactic medium (IGM) at z ≳ 6. The simulations account for the hydrodynamical feedback from photoionization heating and the explosion of massive stars as supernovae (SNe). Our reference simulation, which was

We present results from a Chandra observation of Ross 154, a nearby (2.93 pc) flaring M dwarf (M4.5Ve). During the 57-ksec ACIS-S exposure, a very large flare occurred in which the counting rate increased by over a factor of 100, with an even larger increase in total X-ray power. For the earlier part of the lightcurve, we analyze photon arrival

On the basis of the Galactic O Star Spectroscopic Survey (GOSSS), we present a detailed systematic investigation of the O Vz stars. The currently used spectral classification criteria are rediscussed, and the Vz phenomenon is recalibrated through the addition of a quantitative criterion based on the equivalent widths of the He i λ4471, He ii λ4542

The way in which the effect of the instrumental polarization of a spectrograph can distort the shape of the intensity profiles in sunspots is shown empirically. A spectral region around a magnetically sensitive line and a sunspot away from the disk center were chosen. The resulting limitations which arise when trying to derive physically meaningful