The kinetic equilibrium of Nd II -Nd III in the atmospheres of A-type stars is investigated for the first time with a model atom containing 1651 levels of Nd II, 607 levels of Nd III, and the ground state of Nd, IV. NLTE leads to an overionization of Nd II resulting in weakening the Nd II lines at mild neodymium overabundances relative to the solar Nd abundance ([Nd/H] $\lt$ 2.5) and produces the opposite effect at the higher [Nd/H] values. NLTE abundance corrections grow with effective temperature and reach $\sim$0.6 dex at $\Teff$ = 9500 K. The Nd III lines are strengthened compared with LTE. NLTE abundance corrections range between -0.3 dex and -0.2 dex for $\Teff$ between 7500 K and 9500 K. Therefore NLTE effects may explain ionization discrepancies up to 0.8 – 0.9 dex, derived with the LTE approach.

NLTE effects are even larger for a stratified Nd abundance distribution compared with a homogeneous one resulting in positive NLTE abundance corrections up to 1.4 dex for the Nd II lines and negative ones as small as to -0.5 dex for the Nd III lines. The influence of uncertainty in the photoionization cross-sections on NLTE results is investigated. NLTE calculations were applied to Nd analyses in the atmospheres of roAp stars $\gamma$ Equ and HD 24712.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We observed the magnetic field of the CP star $\alpha^2$ CVn with the 6-m telescope and the echelle-spectrometer (spectral resolution $R=50000$, spectral range $\lambda\lambda 3400--4100$) using a CCD device and Zeeman analyzer. The longitudinal magnetic field $B_{\rm e}$ measured using lines with wavelengths shorter than the Balmer jump ($\lambda 3646$) are systematically 25% smaller at all rotational phases compared with measurements made in the region $\lambda > 3646$. Because in general lines with $\lambda > 3646$ form at deeper levels than lines with $\lambda < 3646$ we get additional evidence for the increase of $B_{\rm e}$ with depth in the atmosphere of $\alpha^2$ CVn.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The convection code of Nordlund & Stein has been used to evaluate the 3D, radiation-coupled convection in a stellar atmosphere with $T_{\rm eff} = 7300$K, log $g = 4.3$ and $[{\rm Fe}/{\rm H}]= 0.0$, corresponding to a main-sequence A9 star. I present preliminary comparisons between the 3D-simulation and a conventional 1D stellar structure calculation, and elaborate on the consequences of the differences.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

In addition to revealing spherical harmonic degrees, $\ell$, of excited modes, pulsational amplitudes and phases from multicolour photometry and radial velocity data yield valuable constraints on stellar atmospheric parameters and on subphotospheric convection. Multiperiodic pulsators are of particular interest because each mode yields independent constraints. We present an analysis of data on the twelve modes observed in FG Vir.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Spectroscopic mode identification techiques, which monitor intensity variations across an absorption line, provide the possibility of determining the quantum numbers l and m, the inclination and the intrinsic pulsation amplitude of a star. Of course, the uncertainties of the mode identification are dependent on the quality of the observations and the identification method applied. We have focused on the Pixel-by-pixel method/Direct line profile fitting (Mantegazza 2000) and the Moment method (Balona 1987, Briquet & Aerts 2003) for pinpointing mode parameters and tested the impact of various observational effects and stellar properties on the identification.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We collected published measurements of the effective magnetic fields of stars on the Main Sequence and above it, and compliled a catalogue of periodic $B_{\rm e}$ variations. We present magnetic phase curves for 139 stars and tables of their parameters. Most of catalogued objects are chemically peculiar A and B type stars (134 stars).To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

A comprehensive overview of the $\lambda$ Bootis stars is presented. This small group (only a maximum of 2% of all objects in the relevant spectral domain) are Population I late B to early F-type stars, with moderate to extreme (up to a factor 100) surface underabundances of most Fe-peak elements and solar abundances of lighter elements (C, N, O, and S). They form a separate group among the classical chemically peculiar objects of the upper Main Sequence as their underabundances are quite outstanding. The basic membership criteria as well as the theories to explain the $\lambda$ Bootis phenomenon are covered. New observations including detailed elemental (surface) abundances, tests for pulsational instability, fluxes in the IR region, and measurements from the Hipparcos satellite permit one to make a statistical sound analysis of the group properties. Details of the evolutionary status, abundance pattern and tests for developed theories are presented.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

In this proceeding we present the method and results of the search for galaxy groups or clusters in the vicinity of the line-of-sight towards lensed quasars.We have studied a sample of ten quasars, using deep ESO/VLT FORS1 and ISAAC images, as well as archive HST/WFPC2 and NiCMOS data. We find that there is most probably a galaxy group towards CTQ 414, HE 0230-2130, B 1359+154, H 1413+117, SBS 1520+530 and HE 2149-2745, with masses $\leq$4~10$^{14}$M$_\odot$h$^{-1}$. Considering its photometric redshift, the galaxy group discovered in the field around HE 1104-1805 is associated with the quasar rather than with the lensing potential. We also conclude that the pair LBQS 1429-0053-A and LBQS 1429-0053-B is a genuine binary quasar rather than a lensed quasar.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Using Kurucz's ATLAS9 model atmospheres I performed LTE fine analyses of the supergiants 4 Lac and $\nu$ Cep. The spectra were obtained at 1.22-m telescope of the Dominion Astrophysical Observatory (DAO) by Saul J. Adelman. The atmospheric parameters were derived using the wings of ${\rm H}\beta$ and ${\rm H}\gamma$ profiles for each star, and from Fe I/II, Fe II/III, and Si II/III equilibria for 4 Lac, and from Fe I/II and Cr I/II equilibria for $\nu$ Cep. A microturbulence of $2.7\,{\rm km\,s}^{-1}$ for 4 Lac was found from Fe II lines while a mean value of $5.2\,{\rm km\,s}^{-1}$ for $\nu$ Cep from Cr II, Ti II and Fe II lines. The rotational and macroturbulent velocities are, respectively, $14\pm2{\rm km\,s}^{-1}$ and $15\pm 2\,{\rm km\,s}^{-1}$ for 4 Lac, and $26 \pm 2{\rm km\,s}^{-1}$ and $12 \pm 2{\rm km\,s}^{-1}$ for $\nu$ Cep. Their He, CNO and light element abundances are solar or overabundant while their iron peak and heavy element abundances are solar or underabundant. The derived results show that 4 Lac has nuclearly processed matter in its photosphere while $\nu$ Cep does not.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We report on a number of ongoing experiments to obtain spectrophotometric data of lensed quasars. We find that spectral differences are a widespread phenomenon, suggesting that microlensing is very common. We discuss some aspects of how to distinguish microlensing from other sources of spectral differences. Extinction by intervening dust can have similar broad band signatures, but can be distinguished or even separated from microlensing using spectrophotometry. We present recent results on extinction and microlensing in a $z=0.93$ lensing galaxy. We also present a case study of the issue of discrepant flux ratios in a quadruple QSO, where we find that microlensing probably plays a role. We finally discuss the aspect of microlensing-induced emission line profile variations.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present new results of our ongoing project to find new magnetic stars in stellar groups and open clusters. Observations are carried out at the 6-m and 1-m telescopes of the Special Astrophysical Observatory. Candidates are selected by analyzing the profiles of the λ5200 broad, continuum features with low resolution spectra (a modification of the Cramer & Maeder method). These candidates are observed then with high resolution and a Zeeman analyzer. We present the measurements of 6 new magnetic stars and discuss results for 2 stars with outstanding magnetic fields. To date we found 31 new magnetic stars, listed for the most part in catalogues of stellar groups. Several stars have very strong magnetic fields, among them is the SrCrEu star HD 178892 with a surface magnetic field ${\rm B}_{\rm s}\geq 20\,{\rm kG}$.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We discuss different physical aspects that may influence pulsation stability in rapidly oscillating Ap stars. We pay particular attention to the role of the magnetic field, atomic diffusion and winds and point out some of the important uncertainties involved in present studies of pulsation stability in these stars. We argue that presently the models that best reproduce the observations are those with convection suppressed, diffusion of helium, and no winds. With these models, in the region of the HR diagram where most roAp stars have been found, we predict the excitation of high order modes and the damping of low order modes, in accord with observations.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

NOELS: What are the uncertainties in the di.usion velocities? What can we do if we would like to multiply or divide it by something? How can we play with that? What would be your best guess?To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Almost a century after its discovery, the phenomenon of amplitude and/or phase modulation, observed in a large percentage of the RR Lyrae stars, still lacks a widely accepted theoretical understanding. Recent attempts to theoretically explain the effect focus on two alternatives, the magnetic models and the resonances models, both involving the presence of nonradial pulsation components.

We present the ‘Blazhko project’, a large international collaboration focused on understanding the Blazhko effect. The aim of the ‘Blazhko project’ is to combine spectroscopic and photometric data from a sample of well-selected Blazhko and nonBlazhko stars, to reveal decisive information on the physical mechanism responsible for the modulation.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

A-type supergiants are the primary targets for the quantitative spectroscopy of individual stars in nearby galaxies because of their intrinsic brightness. An overview is given on the non-LTE techniques required for their analysis. Applications concentrate on placing observational constraints on evolutionary models for massive stars and their host galaxies by detailed abundance analyses. Results from high-resolution studies of A-type supergiants in Local Group galaxies and from intermediate-resolution multi-object spectroscopy of supergiants far beyond the Local Group are summarised.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

SHIBAHASHI: I would like to know how many unknowns – how many equations – you must solve for in the inversion procedure in your new magnetic Doppler imaging method?To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present the results of 3–D nonlinear simulations of magnetic dynamo action by core convection within A-type stars of 2 $M_{\odot}$ with a range of rotation rates. We consider the inner 30% by radius of such stars, with the spherical domain thereby encompassing the convective core and a portion of the surrounding radiative envelope. The compressible Navier-Stokes equations, subject to the anelastic approximation, are solved to examine highly nonlinear flows that span multiple scale heights, exhibit intricate time dependence, and admit magnetic dynamo action. Small initial seed magnetic fields are found to be amplified greatly by the convective and zonal flows. The central columns of strikingly slow rotation found in some of our progenitor hydrodynamic simulations continue to be realized in some simulations to a lesser degree, with such differential rotation arising from the redistribution of angular momentum by the nonlinear convection and magnetic fields. We assess the properties of the magnetic fields thus generated, the extent of the convective penetration, the magnitude of the differential rotation, and the excitation of gravity waves within the radiative envelope.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Several observational anomalies seem to confirm the presence of abundance gradients as a function of depth in different types of chemically peculiar stars. Results emanating from the construction of model atmospheres that take into account the abundance gradients caused by radiative diffusion will be presented. The atmospheric structure, which is calculated self-consistently along with the abundance gradients, will be compared to models with homogeneous abundances. Recent improvements brought to these models will be discussed, along with the intricacies of these calculations and the remaining uncertainties. Several possible applications of such models will also be presented.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The gravitational microlensing experiments in the direction of Large Magellanic Cloud (LMC) predict a large amount of white dwarfs ($\sim$ 20%) filling the galactic halo. However, the predicted white dwarfs have not been observed at the galactic halo. To interpret the microlensing results and resolving the mentioned problems, we use the hypothesis of spatially varying mass function of MACHOs, proposed by Kerins & Evans (1998) (hereafter KE). However the KE model is not compatible with the duration distribution of events (Rahvar 2004a). Here we use more realistic power-law model of MF, $dn/dm\propto m^{\alpha}$ for the MACHOs of halo. The index of MF in this model changes from $-2.7$ for stars with $m>1 M_{\bigodot}$ at the central part of galactic halo to the substellar regime with an upper limit of $-1$ at the edge of halo. We show that in contrast to the abundant brown dwarfs of galactic halo, heavy MACHOs can be responsible for the microlensing events in the direction of LMC.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present results of the analysis of spectroscopic time-series observations of the roAp star HD 24712 obtained at the phase of magnetic maximum. As in previous investigations of roAp stars we found that only lines of the rare-earth elements (REE) show RV pulsational variations. These pulsations in HD 24712 are characterised by gradual phase shifts between RV curves of different REE. The same pulsations of HD 24712 were observed in 2001, giving strong evidence for the stability of the pulsational mechanism in this star. NLTE calculations of Nd line depth formation in stratified atmosphere of HD 24712 allowed us to study the pulsational phase distribution with optical depth, providing strong evidence for a running wave, propagating outward with nearly constant RV amplitude.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html