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

Using observational data published as phase curves of the effective magnetic field strength $B_{\rm e}(P)$ and the surface field $B_{\rm s}(P)$, magnetic models of three stars with long rotational periods are calculated by the Magnetic Charge Distribution method. For two of these stars (HD 2453 and HD 12288), the structure of the magnetic field can be described well by a central dipole model. The third star (HD 200311) is better fitted by a model of a displaced dipole, being decentered by $\triangle r = 0.08 R$ along the dipole axis.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 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

The global bipolar structure of the magnetic surface field is asymmetric for many stars, making its analytical description by an expansion of spherical harmonics problematic because of the coordinates. Landstreet (1970) proposed that the asymmetry could be understood assuming a decentered magnetic dipole in the stellar interior. Its surface field can be calculated for different arrangements inside and outside the star using the Magnetic Charge Distribution method. We demonstrate the effect for the two cases of the shift of the dipole along and perpendicular to the radial direction.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

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

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

The complicated and intricate time-dependent behavior of the magnetic field of $\beta$ Lyrae from 1980 to 2004 is discussed.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

High $S/N$ high-resolution spectroscopic observations of seven bright well-known $\lambda$ Bootis stars: HD 31295, HD 91130, HD 110411, HD 125162, HD 183324, HD 192640, and HD 221756 are presented. Sharp absorption details observed in the bottoms of the Na-D lines in HD 192640 and HD 221756 do not show any radial velocity changes with an accuracy up to $1\,{\rm km\,s}^{-1}$. They are of interstellar origin. Manifestations of non-radial pulsation reported earlier in literature are observed both in the Na-D and the ${\rm H}\alpha$ line profiles. The Inglis-Teller formula was used to evaluate the electron density in the upper atmospheric layers ($\tau \sim 0.1$). The values obtained for $\log{N_e}$ are typical for normal A stars with similar effective temperatures and spectral classes.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present a new method of phenomenologically modelling light curves of variable stars using Principal Component Analysis techniques that provide a realistic description of the variability with a minimum of free parameters. Examples of this method are demonstrated for the magnetic CP stars HD 90044 and HD 125248.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Elemental abundance analysis are derived for the Mercury-Manganese stars HR 4817 (B8 II/III) and $\mu$ Lep (B9 IV) using CCD recorded exposures obtained at the EBASIM echelle spectrograph at the 2.1-m CASLEO (Complejo Astronómico El Leoncito) telescope in Argentina. The spectra coverage is 390-900 nm. The results are compared with previous analyses made with spectra taken using the REOSC echelle spectrograph at CASLEO, the coudé feed telescope at Kitt Peak National Observatory, and/or with the Dominion Astrophysical Observatory coudé spectrograph. As these new spectra go farther into the red and have better resolution than those obtained with the REOSC, we could make better abundance determinations.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

An internacional project “Lithium in magnetic Ap stars” has been run since 1996 with the purpose of creating an observational database allowing systematic studies of the abnormal occurence of lithium on the surface of cool Ap stars. The 2.6 m telescope at the Crimean Astrophysical Observatory, the ESO CAT, ESO 1.52 m telescope with FEROS, the Nordic Optical Telescope, and the 74″ telescope at Mount Stromlo were employed to collect observations at the regions of the lithium resonance lines $\lambda 6103$ and $\lambda 6708 \AA$.

Observations of the roAp-stars HD 83368, HD 60435 and HD 3980 revealed considerable periodical Doppler shifts of the line of lithium $\lambda 6708 \AA$ which can be explained by the presence of lithium spots on their surfaces. Conjunction with structures of the magnetic field is apparent.

A detailed study of the blend at $\lambda 6708 \AA$ in HD 101065 confirmed the anomalous overabundance of lithium amounting to 3.1 dex, as well as unusual isotopic ratio $^6{\rm Li}/^7 {\rm Li} \sim 0.3$.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

I derived the elemental abundances of metallic-line star 2 UMa, using high-dispersion, high signal-to-noise ratio spectra obtained from Dominion Astrophysical Observatory. This study used Kurucz's ATLAS9 and WIDTH9 programs. The star was selected as 1) it has not been the subject of a detailed elemental abundances analysis, and 2) it is relatively sharp-lined and hot enough so that the continuum can be well placed even in the blue. For even cooler Am stars determining the continium will be a major problem. As a guide for the broad-lined and cooler Am stars, a spectral line atlas of 2 UMa will be prepared.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The study of orbital parameters of multiple Ap stars may lead to new suggestions about the origin and magnetic properties of the components. 53 Cam is one of the best studied binaries among Ap stars. However, the nature of its secondary star remains unclear despite the wealth of spectroscopic observations. The system was first directly resolved by speckle interferometry method in 1980 at the 4 m KPNO telescope McAlister et al. (1983). The authors supposed that the magnitude difference between the components could be close to zero. From that time, 16 speckle measurements of the system were made, including 7 observations collected with the SAO 6 m telescope. In addition to relative positions of the components, speckle observations from the 6 m telescope provide high accuracy magnitude difference estimates.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present samples from a spectroscopic atlas of the sharp-lined, magnetic Chemically Peculiar star HR 8216 (A6pCr) based on spectrograms obtained with the long camera of the 1.22-m telescope of the Dominion Astrophysical Observatory using a Reticon detector. For the spectral region $\lambda\lambda 3830-4770$ the inverse dispersion is $2.4\,\AA\,mm^{-1}$ with a 2 pixel resolution of 0.072 Å. At the continuum the mean signal-to-noise ratio is 200. The wavelengths in the laboratory frame, the equivalent widths, and the identifications of the various spectral features are given. This atlas should provide useful guidance for studies of similar stars and for atomic physicists interested in improving atomic line parameters.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We report the results of the spectral monitoring of the chemically peculiar (CP2) star HD 3980 in the Li I$\lambda 6708$ spectral region. High spectral resolution observations ($R=88000$) were carried out at Mount Stromlo Observatory with the 74-inch telescope and the echelle spectrograph. HD 3980 is a late type Ap SrCrEu star with strong double-wave photometric variations in the visible and in the near infrared. We estimated the effective temperature, surface gravity, mass, luminosity, and radius of this star. The monitoring of this star shows strong spectral variations, especially in the profile of Li I$\lambda 6707.8$. We studied the variations of the equivalent width and position of the Li I line as a function of the rotating phase and compared them with the magnetic field variations and light curves taken from the literature. The synchronism of the variations of the Li I line profile, light curve, and magnetic field strength can be explained in terms of the oblique magnetic rotator model. The strong variations of position and intensity of this line with the rotation phase enable us to consider this star as a new member of the intriguing group of “Li-spotted” CP stars.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

The lines of lithium at $\lambda 6708$ and $\lambda 6103$ are analyzed in high resolution spectra of some sharp-lined and slowly rotating roAp stars. Three spectral synthesis codes, STARSP, ZEEMAN2 and SYNTHM were used. New lines of the Rare Earth Elements from the DREAM database, and lines calculated on the basis of the NIST energy levels were included. Magnetic splitting and other line broadening processes were taken into account. Enhanced abundances of lithium in the atmospheres of the stars studied are obtained for both lithium lines. High estimates of $^6{\rm Li}/^7{\rm Li}$ ratio ($0.2\div0.5$) for the studied stars can be explained by Galactic Cosmic Ray (GCR) production by spallation reactions and the preservation of the original $^6{\rm Li}$ and $^7{\rm Li}$ by the strong magnetic fields.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html