Opacity sampling with ATLAS12, the stellar atmosphere code developed by R.L. Kurucz, cannot always be carried out with the desired frequency or depth resolution because of the limited computing power of even the fastest monoprocessors. There are also known problems of portability which make it difficult to run ATLAS12 with various compilers on different operating systems.

We first created a Fortran77 version that can be compiled using the g77 compiler, a useful feature for astronomers having no access to VMS compatible Fortran compilers. As a further step, ATLAS12 was successfully ported to Ada95, an object-oriented parallel language. ATLAS12 is now platform independent, split up in modules and running in parallel on multi-processor machines. Any limitations as to the maximum number of depth and frequency grid-points and the number of lines that can be treated have been pushed far beyond what is possible with the original version.

We intend to incorporate the continuous opacity routines of ATLAS12 in our new CAMAS code for magnetic atmospheres (but also in the existing COSSAM and CARAT codes) to be able to compare our results with Kurucz's de facto stellar atmosphere standard.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

For the first time the possible presence of radial gradients of magnetic fields in the atmospheres of three magnetic Ap stars has been critically examined by measurements of the mean magnetic field modulus from spectral lines resolved into magnetically split components lying on the different sides of the Balmer jump. A number of useful diagnostic lines below and above the Balmer discontinuity, only slightly affected by blends, with simple doublet and triplet Zeeman pattern have been identified from the comparison between synthetic spectra computed with the SYNTHMAG code and the high resolution and $S/N$ spectra obtained in unpolarized light with the ESO-VLT UVES spectrograph. For all three stars of our sample, HD 965, HD 116114 and 33 Lib (HD 137949), an increase of the magnetic field strength of the order of a few hundred Gauss has been detected bluewards of the Balmer discontinuity. These results should be taken into account in future modelling of the geometric structure of Ap star magnetic fields and the determination of the chemical abundances in Ap stars with strong magnetic fields.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We have a project, under the aegis of the Nearby Stars (NStars)/Space Interferometry Mission Preparatory Science Program to obtain the spectra, the spectral types, and, where feasible, the basic physical parameters for the 3600 dwarf and giant stars earlier than M0 within 40 parsecs of the Sun. There are 66 B-to-early-F stars among the first 664 stars analyzed in the Northern hemisphere, and 38 of the same among a similar number of Southern hemisphere stars. With these we can start looking at the statistics of Ap, Am, $\lambda$ Boötis, and other A-type stars for a volume-limited sample, and we can find out just how well we know our neighbors. The project's data are available on our website, http://stellar.phys.appstate.eduTo search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Among variable stars, $\delta$ Scuti are particularly interesting since they can pulsate in different evolutionary phases and are characterized by both radial and nonradial pulsation modes. Even if the majority of $\delta$ Scuti stars are in their Main Sequence (MS) or post-MS phases, there are growing evidences in the recent years about the presence of $\delta$ Scuti variables among stars which are still in their pre-MS phase (the so-called Herbig Ae-stars). Due to the small number of the known class members, the boundaries of Instability Strip are not well constrained. In this context, we present the preliminary results of a long term project to define these limits by enlarging the sample of PMS $\delta$ Scuti stars.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Dworetsky: In the blue metal poor stars shown by you (from C. Sneden) you had a lot of Pb. Were there any signs of Hg, Mn, or Y, typical signatures of diffusion? Or is nuclear processing a sufficient explanation without diffusion?To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The profile of a stellar spectral line is formed by the transfer of radiation through the atmosphere by atomic processes in different chemical elements distributed usually unequally over the surface of a magnetic star.

The theory of model atmospheres accounts for all possible physical conditions. Usually one assumes chemical homogeneity with a plane parallel atmosphere. The resulting line profile, however, is strongly deformed by the geometrical influence of the topographic element distribution and the magnetic surface field structure as well as the projection onto the line of sight of the outgoing radiation from all surface points and its integration over the visible disk.

Line formation by the geometry of projection and element distribution is used for the inverse procedure of Doppler Imaging by V.L. Khokhlova and her followers. We consider here only the influence of the magnetic field on the line profile including the Stokes parameters $I, Q, U, V$, which we study separately from other effects. Thus as a function of the stellar aspect due to rotation the magnetic field and the projection make a symmetric “plane atmosphere profile” asymmetric.

Line profile deformation by the magnetic field leads to a fatal consequence for the traditional measurement of stellar magnetic fields by the Zeeman displacement of the circularly polarized $\sigma$-components. The large scatter of measuring points is partly due to the asymmetry of the line profiles!To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The rotational evolution of the radiative zone of magnetic Ap stars is investigated with numerical simulations. An angular-velocity profile decreasing with axis distance in combination with a magnetic field leads to a magnetorotational instability. The resulting flows efficiently transport angular momentum outwards. The corresponding decay of angular-velocity gradients in the radiative zone is estimated to take about 10–100 million years.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

DG Leo is a spectroscopic triple system showing $\delta$ Scuti type photometric and spectroscopic variations. The three components have nearly equal masses but different chemical compositions in the outer layers. All three are potential pulsators. Frequency analyses of the photometric data were carried out using various methods. These global results together with those of the spectroscopic analysis permit us to discuss of the behaviour of each component with respect to pulsation.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

While there is convincing evidence that the central regions ($r \ll R_e$) of early-type galaxies are dominated by stars and that the outer regions ($r \gg R_e $) are dominated by dark matter, the structure of early-type galaxies in the transition region (a few effective radii $R_e$) between the stars and the dark matter is unclear both locally and in gravitational lenses. Understanding the structure of galaxies in this transition region is a prerequisite for understanding dark matter halos and how they relate to the luminous galaxy. Potentially the best probe of this region is the sample of $\sim 80$ strong gravitational lenses. I review the determination of mass distributions using gravitational lenses using image positions, statistics, stellar dynamics, time delays and microlensing. While the present situation is confusing, there is little doubt that the existing problems can be resolved by further observations.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We are conducting a magnetic survey of a sample of about 30 spectroscopically identified Ap stars, with weak or previously undetected magnetic fields. For 28 studied stars, we have obtained 25 detections of Stokes V Zeeman signatures. Our results suggest that all Ap stars are magnetic. Further there may exist a minimum field strength for which Ap-type characteristics are produced.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Components of multiple systems generally originate from the same protostellar environment. Their similarities or differences in surface chemical composition therefore relates to their individual evolutionary paths (stellar evolution, rotation) and the possible influence of a close companion.

DG Leo is a spectroscopic hierarchical triple system with almost equal-mass late-A type components. Observations with high time and high spectral resolution were used to disentangle the spectrum of each component from the composite spectra. A detailed abundance analysis of the component spectra reveals that the wide companion has a nearly solar-like composition, while both components in the close binary show Am type peculiarities.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We calculated the energy distributions of A-star atmospheres (${{T}_\text{eff}=10 000}\,{\rm K},{\log g=4.0}$) for ranges of the abundances of silicon and other light chemical elements using adequate model atmospheres. We discuss the reasons for and the magnitudes of the calculated departures of the stellar energy distribution and uvby magnitudes from those of normal stars.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

This article reviews the methods of measurement which allow us to infer the presence of magnetic fields in (A) stars. Beginning with the basic observational consequences of the Zeeman effect, we describe various modern spectroscopic and polarimetric techniques which allow us to directly detect and characterise magnetic fields in stellar photospheres. Sometimes, nature conspires to make such detections difficult, forcing us to rely on indirect (proxy) indicators of magnetism. This talk will also briefly discuss a number of these indirect field indicators, some of which demand space-based observations.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Scalar-tensor (ST) theories of gravity are the best motivated alternative to general relativity (GR), arising in every high-energy theory attempting to unify all the fundamental interactions. Furthermore, accomodating an arbitrary number of scalar fields, ST theories yield to cosmological scenarios with a dynamical realization of the dark energy. Solar-System experiments and binary-pulsars observations are compatible with very small departures from GR on the local universe ($z\simeq 0$); on cosmological scales, big-bang nucleosynthesis and cosmic microwave background (CMB) observables can admit larger deviations from the predictions of GR. Weak lensing could provide a test for ST theories of gravity on intermediate scales. Based on a code developed to study ST theories on CMB observables, we implemented a plug-in code to compute the convergence power spectrum and some 2-points statistics. Preliminary results using a simple model of ST theory are presented. This study is aimed to constraint classes of ST models.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

KUBÁT: What are the differences between both codes for convection simulations without magnetic fields which we have just seen?

FREYTAG: Both codes solve the same set of basic equations and rely on very similar fundamental assumptions. However, the algorithms used to solve the hydrodynamics or the radiation transport equations differ. The codes have no routines in common. There is an ongoing project to perform a simulation of solar granulation with both codes, relying on the very same settings (grid, model extension, equation of state, opacities, ray system, etc.). The remaining differences are tiny, for example, much smaller than the difference between the 2D and the 3D models. Both codes have some extensions (for instance dust or magnetic field) not (yet) found in the other.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We briefly review the traditional classifications of CP stars. The current availability of large numbers of abundances now make it possible to use multivariate techniques, both to supplement traditional classification methods and probe the abundance patterns. We discuss cluster analysis and correlation matrices for sample material. We review the historical resistance to the notion that CP stars were indeed chemically peculiar. Modern work shows that while these objects do indeed have atmospheric anomalies, they are nevertheless chemically peculiar.

Abundance patterns are an important clue to the origin of the abundance peculiarities. We contrast patterns due to nuclear and chemical differentiation processes. The roAp and related stars show vertical as well as horizontal abundance variations, and abnormal line profiles. Photospheric abundances in these stars are surely abnormal (nonsolar), but as long as the models are uncertain the derived abundances will be very crude.

For more than two decades, observations of CP stars in the X-ray and radio regimes have been made with increasing sensitivity and pointing accuracy. We discuss the current evidence linking magnetic and nonmagnetic CP stars to sources of galactic X-rays and radio radiation. There seems no doubt that high energy phenomena are associated with, if not produced by, some CP stars. This circumstance admits the possibility that the release of high energy particles (p's, n's and $\alpha$'s) during such events may initiate nuclear reactions on the surfaces of the CP stars. We briefly reconsider the viability of such processes for producing exotic species like Pm by proton bombardment using recent data for solar and stellar flares.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Ultra-high signal-to-noise, high dispersion spectroscopy over the wavelength range \mbox{$\lambda 4487 - 4553$} shows Vega to be a rapidly rotating star $(V_{\rm eq}\sim 160\,{\rm km\,s^{-1}})$ seen almost pole-on. These data, analyzed anew, are combined with analyses of the hydrogen lines (${\rm H}\gamma, {\rm H}\beta$ and ${\rm H}\alpha$) and the latest absolute continuum flux for Vega to yield the following results: $V \sin i=21.9\pm 0.1\,{\rm km\,s^{-1}}$, polar $T_{\rm eff}=9680\pm 10\,{\rm K}$, polar $\log g=4.00\pm 0.02\,{\rm dex}$, $V_{\rm eq}=160\pm 10\,{\rm km\,s^{-1}}$, $\xi_{\rm T}=1.08\pm 0.02\,{\rm km\, s^{-1}}$ and $i=7.9\pm 0.5^{\circ}$. The variations in $T_{\rm eff}$ and $\log g$ over the photosphere total 350 K and 0.06 dex, respectively. The mean $T_{\rm eff}=9510\pm 10\,{\rm K}$ and mean $\log g=3.97\pm 0.02\,{\rm dex}$ agree with the spherical model values derived here and by others.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Both components of the composite-spectrum binary o Leo have Am characteristics, even though the primary is an evolving giant ($\log g=3.25$) with $T_{\rm eff} \sim 6100\,{\rm K}$. This is believed to be the first isolation of such a cool Am star. The finding challenges the theories of diffusion which are widely accepted as the cause of metallicism. The primary component (o Leo A) appears to be deficient in Ca and Sc, as are classical Am stars. Its unusual state may be attributable either to its current state of rapid evolution, or to regular Am-star evolution that is difficult to recognize spectroscopically. A full account of this research appeared in AJ 123, 988-1001, 2002.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We report irregular changes in the line profiles of Deneb, and suggest that they represent part of the mechanism causing the stellar wind.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The Hubble Deep Field (North) and the flanking fields are used investigate the occurrence of multiple weak lensing deflections along the line of sight in relatively deep imaging data ($z_{\rm lens} \sim 0.6$, $z_{\rm source} \sim 1.2$). Ray tracing simulations of galaxy–galaxy lensing in the HDF-North show that proper inclusion of multiple weak deflections is important for a correct prediction of the net shear for most sources, and for a given source redshift the number of multiple weak deflections is largely insensitive to the cosmography. The effects of multiple weak deflections on the magnitude of the weak lensing signal are, of course, strong functions of the adopted halo parameters. Independent of the halo parameters, however, the closest lens to a source (in projection on the sky) is not the strongest lens in the case of more than 50% of the sources which acquire a net shear of $\gamma \lo 0.01$. In addition, multiple weak deflections result in a tangential shear about the lens centers that is greater than the tangential shear that would occur if source galaxies were lensed solely by the closest lens. Further, multiple weak deflections give rise to correlated image ellipticities and account for a substantial amount of the total cosmic shear signal on small angular scales in $\Lambda$CDM and open CDM models.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html