ar X iv : a st ro - p h / 98 05 23 4 v 1 1 8 M ay 1 99 8 An abundance analysis for Vega : Is it a λ Boo star ?

ar X iv : a st ro - p h / 98 05 24 3 v 1 1 9 M ay 1 99 8 ι Cas : Multi - element Doppler imaging and magnetic field geometry

In order to clarify the role of the magnetic field in generating abundance inhomogeneities in the atmospheres of Ap stars, we present new abundance Doppler images and an approximate magnetic field geometry for the Ap star ι Cas.

ar X iv : h ep - p h / 98 05 30 4 v 1 1 3 M ay 1 99 8 Λ b → Λ c P ( V ) Nonleptonic Weak Decays

ar X iv : a st ro - p h / 98 05 05 1 v 1 6 M ay 1 99 8 The λ Bootis stars

In this article the current knowledge of the group of λ Bootis stars is reviewed. These metal poor objects are quite outstanding compared to other chemically peculiar stars of the upper main sequence. Up to now no theory has been developed which is able to explain the majority of observational results. This article is mainly focused on the work which needs to be done in the future in order to c...

ar X iv : a st ro - p h / 98 05 21 3 v 1 1 5 M ay 1 99 8 Light element abundances in He - rich stars

We present an abundance analysis of light elements in He-rich stars. The analysis is based on both low and high resolution observations collected at ESO, La Silla, Chile in the optical region and includes 6 standards and 21 He-rich stars. Light-element abundances display a diverse pattern: they range from under-solar up to above-solar values.

ar X iv : a st ro - p h / 98 05 05 3 v 1 6 M ay 1 99 8 Dust and Gas around λ Bootis Stars

High-resolution spectra of λ Bootis stars reveal the presence of circumstellar gas for example in the Ca K line. The example of the normal A star β Pictoris shows, that the narrow stable absorption component in Ca K can be reproduced using appropriate disk models and a calcium underabundance in the circumstellar gas of a factor of ∼ 30. Similar models are suggested for the group of metal-defici...