We have started an analysis of the sharp-lined superficially normal A3IVp star 95 Leo. We are using $2.4 \AA \mathrm {mm}^{-1}$ spectrograms covering $\lambda\lambda 3830-4934$ obtained with the 1.22-m telescope of the Dominion Astrophysical Observatory using CCD detectors. Their mean signal-to-noise ratios are $\ge\,200$. The spectrograms are rectified and measured with the interactive computer graphics program REDUCE of Graham Hill and his associates. In measuring the spectrum with the VLINE routine, we use the fixed parameter feature to deconvolute metallic line blends and to measure weak lines. Effective temperature and surface gravity estimates based on spectrophotometry and H$\gamma$ profile fitting were given in the literature as 8300 K and 3.65, respectively.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The stellar winds of A supergiants can have a significant influence on their emergent spectra. Here we present the hydrogen line profiles of a model based on the stellar parameters of HD 12953. The radiative transfer equation is solved in two dimensions in axial symmetry. We do not include the velocity field by the Sobolev approximation, but in detail using the Lorentz transformation. This allows us to correctly include the stellar wind, since the velocity gradients in A supergiants are too small for the Sobolev approximation to be valid.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We describe a new project aiming at measuring time delays for most known lensed quasars, from optical light curves obtained with five (almost) dedicated 1-2 m telescopes in the Northern and Southern hemispheres. The goal is to evaluate the Hubble constant H$_0$ with a precision below 2%. We present here numerical simulations in order to define the optimal temporal sampling in our observations as a function of typical quasar variations, object visibility, and for a given accuracy on the individual photometric points. It is also emphasized that the ongoing effort to obtain deep imaging using both space and ground based facilities must be continued, as illustrated by the comparison of HST and VLT near-IR images of the “cloverleaf”: H 1413+117.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The Virtual Observatory (VO) will revolutionise the way we do Astronomy, by allowing easy access to all astronomical data and by making the handling and analysis of datasets at various locations across the globe much simpler and faster. I report here on the need for the VO and its status in Europe, including the first ever VO-based astronomical paper, and then give two specific applications of VO tools to open problems of A-stars research.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We analyse parameters of the average phase curves of the effective magnetic field $B_{\rm e}$ for 139 Main Sequence and other stars. 134 are chemically peculiar A and B type stars. This contribution presents the statistical properties of the fitting coefficients $B_{\rm 0}$, $B_{\rm 1}$, and $B_{\rm 2}$, and the distribution of the parameter $r= B_{\rm e}({\rm max})/B_{\rm e}({\rm min})$.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

A cross-dispersed spectrophotometer with a back-illuminated uv-coated CCD detector and its automated 0.5-m telescope at the Fairborn Observatory, Washington Camp, AZ now under construction, should begin scientific observations in the Spring of 2005. The Citadel ASTRA (Automated Spectrophotometric Telescope Research Associates) Telescope will be able to observe Vega the primary standard, make rapid measurements of the naked-eye stars, use 10 minutes per hour to obtain photometric measurements of the nightly extinction, and obtain high quality observations of $V = 10.5$ mag. stars in an hour. The approximate wavelength range is $\lambda$ 3300-9000 with a resolution of 14 Å in first and 7 Å in second order. Filter photometric magnitudes and indices will be calibrated in part for use as quality checks.

First a grid of secondary standards will be calibrated differentially with respect to Vega. They will also be used to find the nightly extinction. The candidates were selected from the most stable bright secondary stars of the grating scanner era, the least variable main sequence B0-F0 band stars in Hipparcos photometry, and metal-poor stars. Continued measurements of secondary stars will be used to improve the quality of the secondary standard fluxes. Science observations for major projects such as comparisons with model atmospheres codes and for exploratory investigations should also begin in the first year of scientific observations. The ASTRA team realizes to deal with this potential data flood that they will need help to make the best scientific uses of the data. Thus they are interested in discussing possible collaborations. In less than a year of normal observing, all isolated stars in the Bright Star Catalog that can be observed can have their fluxes well measured. Some A star related applications are discussed.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

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