Recent Talks

There are many parameters accounting for the quality of an astronomical site, namely seeing, cloud cover, ground winds, high-altitude winds, etc. The water vapor content is the main parameter affecting the IR quality of astronomical sites. The fraction of nights with good IR conditions (small column of water vapor) as a function of the epoch of the year will allow an optimal scheduling of telescope observing time. Global Positioning System (GPS) is an increasingly operational tool for measuring the precipitable water vapor (PWV). In this seminar, we briefly describe the procedure to estimate the PWV through GPS and we present the statistical results derived from a 7.5-year long time series of PWV estimations derived from GPS at the Roque de los Muchachos Observatory.

Luminous high-redshift radio galaxies (HzRGs) are associated with the most massive known galaxies in the early Universe. These galaxies have the properties expected of the progenitors of dominant galaxies in rich clusters.
I shall describe the properties of HzRGs and demonstrate how they can be used to study the formation and evolution of galaxies and clusters. I shall also show how LOFAR, the new European radio telescope, can be used to extend these probes into the epoch of reionisation.

We test the theoretical prediction that the straightest dust lanes in bars are found in strongly barred galaxies, or more specifically, that the degree of curvature of the dust lanes is inversely proportional to the strength of the bar. The test uses archival images of barred galaxies for which a reliable non-axisymmetric torque parameter (Q_b) and the radius at which Q_b has been measured (r(Q_b)) have been published in the literature. Our results confirm the theoretical prediction but show a large spread that cannot be accounted for by measurement errors. We simulate 238 galaxies with different bar and bulge parameters in order to investigate the origin of the spread in the dust lane curvature versus Q_b relation. From these simulations, we conclude that the spread is greatly reduced when describing the bar strength as a linear combination of the bar parameters Q_b and the quotient of the major and minor axes of the bar, a/b. Thus, we conclude that the dust lane curvature is predominantly determined by the parameters of the bar.

The formation of massive stars is not fully understood. The high luminosity and temperature of massive protostars complicate the accretion mechanism at work in intermediate and low mass young stellar objects. Nonetheless, several scenarios exist to explain the formation of massive stars. In this talk, we will focus on the process of triggered star formation on the borders of H II regions. Due to the feedback effects of OB stars, a layer of molecular material is collected during the expansion of the H II region. Instabilities develop in this layer and give birth to new stars. We will present a detailed study of three Galactic H II regions (RCW79, RCW82 and RCW120). Near-infrared integral field observations have been carried out with SINFONI on the VLT. We will see how they reveal the nature of both the ionizing stars and of the YSOs in the collected layer and how they support the scenario of 'triggered star formation'.

I present some recent results from our Optical and NIR studies of five short period low-mass X-ray binaries (LMXB's; X1822-371, X1957+115, UW CrB, X1916-05 and X0614+091). Optical photometry and spectroscopy reveal some surprising results on the geometry and evolution of accretions discs in LMXB's. Based on our data, it is increasingly clear that accretion discs in these systems are far from being stable and must undergo substantial precession and/or warping behaviour on timescales less than a day in case of the shortest period systems.