Though there are now many hundreds of confirmed exoplanets known, the binarity of exoplanet host stars is not well understood. This is particularly true of host stars which harbor a giant planet in a highly eccentric orbit since these are more likely to have had a dramatic dynamical history which transferred angular momentum to the planet. Here we present observations of four exoplanet host sta...

We show evidence that the red giant star ξ Hya has an oscillation mode lifetime , τ, of about 2 days significantly shorter than predicted by theory (τ = 17 days, Houdek & Gough 2002). If this is a general trend of red giants it would limit the prospects of asteroseismology on these stars because of poor coherence of the oscillations.

We present the analysis of high resolution spectra of six red giant stars in the old open cluster Collinder 261. Reddening values for individual stars, derived from the relation between colours and temperatures (deduced from our fully spectroscopic analysis) are consistent with previous determinations based on photometry. For this cluster we derive an iron abundance of [Fe/H] = −0.03 ± 0.03. We...

We illustrate the application of high precision Strömgren uvby photometry to open and globular clusters (GCs). It is shown how such data can be used to determine cluster ages, independent of distance and only weakly dependent on reddening. We also illustrate in detail how c1 index variations point to significant star-to-star abundance variations of C and N (through variations in the strength of...

An AGB star in a binary system is likely to pollute its companion with carbon-and s-process-rich matter. After the AGB star has faded into an unconspicuous white dwarf, the polluted companion enters the zoo of stars with chemical peculiarities. In this paper, the progeny of AGB stars in binary systems are identified among existing spectroscopic classes (Abell 35-like, binary post-AGB, WIRRing, ...

Context. A well-known bottleneck for the core-accretion model of giant-planet formation is the loss of the cores into the star by Type-I migration, due to the tidal interactions with the gas disk. It has been shown that a steep surface-density gradient in the disk, such as the one expected at the boundary between an active and a dead zone, acts as a planet trap and prevents isolated cores from ...

In order to understand the composition of planetary nebulae we first need to study the nucleosynthesis occurring in the progenitor star during the thermally-pulsing Asymptotic Giant Branch (AGB) phase. I present an overview of single AGB evolution, with an emphasis on the mixing processes that alter the envelope composition, followed by a discussion of the stellar yields available from single A...

Early studies of molecular gas in M33 used the CO J=1-0 transition to map out the total gas content in the inner kiloparsec of the galaxy and to study the properties of the giant molecular cloud population. In this review, I discuss recent detailed studies of individual molecular clouds in M33 in higher rotational transitions of CO, CO, and the fine structure line of atomic carbon. These data r...

We consider the problem of an elliptical background source crossing a linear gravitational lensing fold caustic. We derive a simple expression for the light curve of a source with a uniform surface brightness that is accurate to third order in the ellipticity e (yielding brightness errors of . 1% for e . 0.3). We then consider caustic crossings of a rotating star, an oblate giant extrasolar pla...

The HIPPARCOS parallaxes have provided us with a precise HR diagram (HRD) of the solar neighbourhood, complete within certain limits. The scope of this work is a study of the stellar population densities in characteristic regions of the HRD to test stellar evolutionary time scales. We examine two HRDs (Mv ≤ 4.0), both based on the single-star entries of the HIPPARCOS catalogue. One is constrain...