[P01] Brandão, I.; Cunha, M.S.
The Bolometric Correction of the peculiar pulsating star Alpha Cir
Alpha Cir (HD128898) is the prototype of a class of Ap stars that oscillate in high frequencies. The combination of classical and seismic data of these stars can contribute greatly to the understanding of their structure and evolution. In order to place alpha Cir in the Hertzsprung-Russell (HR) diagram, both effective temperature and luminosity are needed. Since the parallax of the star was measured by Hipparcos, the luminosity can be derived if the apparent bolometric flux is known. Moreover, the apparent bolometric flux can also be used to determine the effective temperature of alpha Cir, if a measurement of its angular diameter is available. In principle, the bolometric flux can be determined from the visual flux if the bolometric correction is known. However, bolometric corrections for normal stars cannot be used when studying Ap stars, since the latter show abnormal flux distributions, with strong flux deficiencies in the ultraviolet relative to normal stars with the same Paschen slope. With this in mind, we have used spectroscopic and photometric data of alpha Cir available in the literature to determine the star's bolometric correction. Two values were determined, both based on an estimation of the total integrated flux of this star. The first result was determined by combining the observed ultraviolet flux (taken from IUE low dispersion spectrum) and the Kurucz model that best fitted the optical and NIR photometry for the star. A second value for the bolometric correction was computed using the same method, but substituting the Kurucz synthetic spectra by the mean of two low resolution spectra of alpha Cir calibrated in flux. A discussion of the two values obtained and their associated uncertainties is provided.

[P02] Castelli, F.; Hubrig, S.
Synthetic Spectra of HgMn stars compared with UVES observations
Results of the spectral analyses of some HgMn stars observed with UVES at high resolution and high S/N are available online in the form of plots of the overimposed observed and LTE computed spectra. The online material is available at http://wwwuser.oat.ts.astro.it/castelli/stars.html. The studied ranges are divided into 6Å wide intervals having identifications, excitation potential of the lower level, and predicted line intensities written above the lines. Complete analyses covering the 3050-9500Å region have been performed for two stars, HD 175640 and HR 6000. Preliminary analyses of some specific spectral ranges are available for a few other stars (i.e. 46 Aql, Feige 86). The online plots show the quality of the agreement between the observed and computed spectra and can also be used as template for other stars of the same spectral type. For instance, HD 175640 is an excellent example of a star very overabundant in Mn ([+2.4]), while HR 6000 is an example of a star overabundant in Fe ([+0.7]).

[P03] Dimitrijevic, M.S.; Ryabchikova, T.; Simic, Z.; Popovic, L.C.; Dacic, M.
Electron-impact broadening of ionized chromium lines for Ap star atmospheres analysis
The influence of Stark broadening on the shapes of Cr II spectral lines observed in stellar atmospheres has been considered. The corresponding Stark broadening parameters for seven multiplets belonging to 4s-4p transitions, were calculated by the semiclassical perturbation approach and applied to the analysis of Cr II line profiles observed in the spectrum of Cr-rich star HD 133792. For stellar spectra synthesis, the improved version of the code SYNTH for synthetic spectrum calculations was used. We found that Stark broadening mechanism is very important and should be taken into account, especially in the study of Cr abundance stratification.

[P04] Dimitrijevic, M.S.; Simic, Z.; Kovacevic, A.; Dacic, M.; Sahal-Brechot, S.
On the Stark broadening of Te I spectral lines for Cp star plasma analysis
With the development of astronomical observations from space, even such trace element lines like the tellurium one become to be observed in stellar spectra. Since the significance of the corresponding atomic data, including Stark broadening parameters increases with the development of space-born spectroscopy, we investigate here theoretically the influence of collisions with charged particles on spectral lines of neutral tellurium. By using the semiclassical perturbation method, Stark widths and shifts of three Te I spectral lines, of interest for modellisation, investigation and diagnostic of stellar plasma have been obtained. Results were applied for the investigation of the influence of Stark broadening mechanism on the CP star spectra.

[P05] Gebran, M.
Abundance determinations of A/F and Am/Fm stars in the Pleiades and Coma Berenices open clusters
Abundances of 18 chemical elements have been derived for 27 A ("normal" and chemically peculiar) and 16 F stars members of Pleiades (age about 100 Myr) and Coma Berenices (age about 450 Myr) open clusters. Assuming LTE, the abundances were determined by minimising the chi-square of grids of synthetic spectra to observed high resolution (R = 42000, 60000, 75000) high S/N echelle spectra obtained at the Observatoire de Haute-Provence (OHP). A semi-automated procedure was used to derive the abundances of C, O, Na, Mg, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Sr, Y, Zr and Ba, the projected rotational velocity vesini and the microturbulent velocity for each star analysed. For all the elements, we found no trend between [X/H] and fundamental parameters (Teff , vesini). For both clusters and for C, Sc, Ti, Cr, Mn, Sr, Y, Zr and Ba, A stars exhibit larger star to star variations in [X/H] than F stars do . [C/Fe] and [O/Fe] are anti-correlated with [Fe/H] for A stars. The scenario of gas to dust separation is mentioned by analysing the trend of [C/Si] versus [Si/H] for A stars. These abundance determinations are confronted to recent evolutionary models of A and F stars including transport processes.

[P06] Gerth, E.; Glagolevskij, Yu.V.
The magnetic field generated by sources inside and outside the star
The ubiquitously in universe present magnetic fields reveal themselves only by physical interaction with the interspersed material, especially by the Faraday and the Zeeman effects. The magneto-sensitive atmosphere of a star is an ideal detector of the magnetic field penetrating the atmosphere layer -- indifferently from which side. Hitherto the origin of the magnetic field of a star was sought for mainly in its interior, neglecting the possibility of externally caused influence. It should not be denied, however, that most magnetic stars possess their own magnetic moment. The detection of a field depends, of course, on its power. Therefore, only nearby powerful magnetic sources may influence recognizable the atmosphere of a star with a sufficiently large surface. One could think of a binary system consisting of a nonmagnetic giant with a magnetic dwarf companion. Scholz and Gerth assume, for instance, that the supergiant νCep, which can not posses an own magnetic moment for physical reasons, could be a candidate for such an externally magnetically influenced "magnetic star". But also other possibilities of external magnetic sources should be taken into consideration, such as close and cataclysmic binary systems with mutual influence. We demonstrate here only the principal possibilities and relate to the advantages of the theoretical, mathematical and numerical treatment of the construction of magnetic fields by sources and vortices.

[P07] Glagolevskij, Yu.V.;Gerth, E.
The magnetic field structure of the slow CP star rotator HD 188041
The slowly rotating CP star HD 188041 is subjected to an analysis of its magnetic field structure by the modelling method of the Magnetic Charge Distribution (MCD), using the photographic measurements of Babcock. The first attempt to fit Babcock's observational results to a model of a central magnetic dipole gives - as usual because of the ambiguous aspect at the north or south hemispheres of the star - two possible solutions of the distance angle of the magnetic and rotational axes β1 = 6o or β2 = 76.8o corresponding to the inclination angles i1 = 80.5o and i2 = 14o. Admitting a decentralization of the dipole, the fitting of the phase curve of Beff to the data by minimizing the sum of the quadratic deviations could be improved, making thus the decentered dipole probable, but changing the angles β and i only slightly.

[P08] González, J.F; Hubrig, S.; Savanov, I.
A search for pulsational line profile variations in the δScuti star HD 21190 and in the Ap Sr star HD 218994.
We report the results of our study of high time resolution UVES spectra of the δScuti star HD 21190, which is supposed to be the most evolved Ap star known, showing δScuti type pulsations with a period of 3.6h, and of the ApSr star HD 218994. This work is the continuation of the discussion of the relationship between the roAp stars and the non- oscillating Ap stars. The results are important in view of calculations done by Cunha (2002, MNRAS, 333, 47) related to the theoretical instability strip for the roAp stars and predicted pulsation periods in the more evolved stars.

[P09] Huber, D.; Saio, H.; Gruberbauer, M.; Weiss, W.W.; Rowe, J.; Hareter, M.; Kallinger, T.; Reegen, P.
MOST & 10 Aql: Shedding New Light on a Mysterious roAp Star
34.5 days of continuous photometry of the roAp star 10 Aql obtained with the MOST space telescope clearly confirm the rapid oscillations of the star and yield an unambiguous identification of three pulsation frequencies as well as two candidate frequencies with low S/N. An attempt to fit the observed frequencies to theoretical non-adiabatic frequencies influenced by a dipole magnetic field with strengths up to 5 kG yields the best fit for a 1.95 solar mass model with homogeneous helium abundance and B ~ 3 kG. The resulting luminosity is in slight discrepancy with the value based on the Hipparcos parallax, due to the low number of fitted frequencies however the results have to be considered with caution.

[P10] Hubrig, S.; González, J.F; Arlt, R.
Spots on the surface of HgMn stars: clues to the origin of Hg and Mn peculiarities
We will present the results of our recent survey of the inhomogeneous distribution of various elements on the surface of Bp stars with Hg and Mn peculiarities. Further, we will discuss the mechanisms that could be responsible for the development of the chemical anomalies in these stars.

[P11] Khalack, V.R.; LeBlanc, F.; Behr, B.; Wade, G.A.; Bohlender, D.
Vertical stratification of iron abundance in atmospheres of Blue Horizontal-Branch stars.
The observed slow rotation and abundance peculiarities of certain Blue Horizontal Branch (BHB) stars suggest that atomic diffusion can be important in their stellar atmosphere and can lead to vertical abundance stratification of chemical species with atmospheric depth. To verify this hypothesis, we have undertaken an abundance stratification analysis in the atmospheres of six hot BHB stars, based on recently acquired McDonald-CE spectra. Our numerical simulations show that iron abundance is vertically stratified in the atmospheres of two stars in M15: B267 and B279. One star WF2-2541 in M13 also appears to have vertically stratified iron abundance, while for WF4-3085 the signatures of iron stratification are less convincing. In all cases, the iron abundances increase toward the lower atmosphere. The other two stars in our sample: WF4-3485 and B84 do not show any significant variations of iron with atmospheric depth. Our results support the idea that atomic diffusion dominates other hydrodynamical processes in the atmospheres of hot BHB stars.

[P12] Kochukhov, O.; Shulyak, D.
New generation model atmospheres for chemically peculiar stars
The atmospheric structure of chemically peculiar stars deviates from that of normal stars with similar fundamental parameters due to unusual chemistry, vertical abundance gradients and the presence of strong magnetic field. These effects are not considered in the classical model atmosphere calculations, possibly leading to large errors in the stellar parameter determination and in abundance analysis. To tackle this problem we used the state-of-the-art opacity sampling model atmosphere code LLmodels to calculate comprehensive grid of new generation model atmospheres for magnetic CP stars. This grid of >200 models covers the whole parameter space occupied by these objects and takes into account temperature dependence of the chemical abundances found in SrCrEu and Si-peculiar stars. Here we present the first results of our model grid calculations. We discuss atmospheric structure, bolometric corrections, photometric indices and energy distributions of peculiar stars and compare them with normal stars of the same fundamental parameters.

[P13] Kochukhov, O.
Zeeman split lines in CP stars: a discovery of low-contrast fields in slow rotators?
Zeeman split lines in the spectra of CP stars are routinely used to measure the surface magnetic field strength. But, at the same time, information provided by the shapes of the resolved pi and sigma components is largely neglected. We show that high-resolution observations of the resolved Zeeman split triplet lines can be used to obtain new constraints on the field structure. In particular, the contrast of the field strength distribution over the stellar surface can be deduced from the differential measurement of the second moment of the Zeeman components. Analysis of the triplet lines in several cool magnetic CP stars uncovers a surprisingly homogeneous field structure, inconsistent with any low-order multipolar geometry. Furthermore, we show that magnetically split triplet lines can be utilized to detect a very slow stellar rotation. Using this technique we detect rotation in the roAp star 33 Librae and directly confirm this finding by observation of the rotational modulation within the profiles of Zeeman resolved lines in this star.

[P14] Kochukhov, O.; Ryabchikova, T.; Bagnulo, S.; Lo Curto, G.
A search of very low amplitude magnetoacoustic pulsations with HARPS
Many time-resolved spectroscopic studies of the rapidly oscillating Ap (roAp) stars have focused on the known, high-amplitude pulsators and did not address the fundamental question of what distinguishes pulsating and non-oscillating Ap (noAp) stars. It has been suggested that there might exist no real dichotomy between roAp and noAp stars and weak pulsational variability is present in all cool Ap stars. With the aim to test this hypothesis and to obtain the first complete picture of the incidence of pulsations in Ap stars, we used the ultra-stable spectrograph HARPS at ESO to obtain time resolved spectra for a sample of noAp stars. Here we report first results of our study. We confirm the presence of ~16-min period pulsations in beta CrB (HD 137909) and demonstrate multiperiodic character of oscillations in this star. Furthermore, we discovered very low amplitude 9-min pulsations in HD 75445 -- an object spectroscopically very similar to known roAp stars.

[P15] Krtička, J.; Kubát, J.; Votruba, V.
Multicomponent stellar winds of B stars
We study multicomponent effects in the stellar winds of B stars. For stars with highest mass-loss rates the usual one-component approach is sufficient. For stars with weaker winds multicomponent effects become important. For these stars either the frictional heating influences the wind temperature, or the decoupling of wind components occurs. For less dense winds hydrogen and helium fall back on the stellar surface or even a pure metallic wind is possible. We discuss the relevance of our results for the explanation of the chemical peculiarity of hot stars.

[P16] Kudryavtsev, D.O.; Semenko, E.A.; Romanyuk, I.I.
HD 45583 - CP star with the complex magnetic field
HD 45583 (V682 Mon) is a member of the open cluster NGC 2232. The star has a very large photometric index Δa = 67 mmag and a relatively short period of rotation P = 1.177177 days. We obtained more than 20 measurements of the star's longitudinal magnetic field during 5 runs of observations. Our observations show that the shape of some lines is different for right-hand and left-hand circular polarizations, the longitudinal field curve shows double-wave variations. It means that HD 45583 has a strong and complex non-dipole magnetic field. We estimated a surface magnetic field Bs to be 34 kG using partially splitted Zeeman components and chemical abundance of some elements (Fe: -3.5, Mg: -4.7, Cr: -4.6, Si: -3.9).

[P17] Mikulášek, Z.; Gráf, T.; Krtička, J.; Zverko, J.; Žižňovský, J.
Photometrically simply behaving mCP stars
We present preliminary results of our study of the light curves of 19 photometrically "simply behaving" magnetic CP (mCP) stars what have their ubvy and Hp light curves mutually similar. The aim is to find the stars with as simple as possible photometric structures on their surfaces that would help us to comprehend the more complicated cases. We confirm at least two types of photometric spots on mCP stars are present: the bright ones in all colors and the dark ones, which in particular causes the v color varies in antiphase with the optical region and which is typical for the coolest mCP stars. Despite our sample includes stars with the simplest light curves we were able to sort out, our analysis indicates that very few of them can be explained with a single photometric spot.

[P18] Mikulášek, Z.; Krtička, J.; Zverko, J; et al.
The record-breaking rotational braking of He strong CP star HD 37776
We study the long-term light and spectral variations in the He-strong magnetic chemically peculiar star HD 37776 (V901 Ori) to search for changes in its 1.5387 d period in 1976--2007. We analyze all available photometric observations as well as spectrophotometry in the He I 4026Å--line. These data are supplemented by 506 own new (U)BV observations obtained during the last two observing seasons, 66 estimates of equivalent widths of the He I spectral lines on 23 CFHT spectrograms from 1986, and 35 SAO Zeeman spectrograms taken in 1994--2002. All of 1895 particular observations obtained by the various techniques are processed simultaneously in our analysis. We confirm the previously suspected lengthening of the period in HD 37776 which is record-breaking among other CP stars. The mean rate of the period increase during the last 31 years is 0.541+/-0.020 s per year. The shapes of observed light curves are invariable. We interpret this ongoing period increase as the slowing down of the star's surface rotation, possibly due to momentum loss through events or processes in the extended stellar magnetosphere.

[P19] Netopil, M.; Paunzen, E.; Maitzen, H.M.
(Extra)galactic Stellar Aggregates
The study of open clusters naturally introduces many advantages, because they are physically related groups of stars held together by mutual gravitational attraction that were formed at roughly the same time from one large cosmic gas and dust cloud. Their evolutionary stages range from clouds where star formation takes still place at this moment to very old aggregates with turn-off points as late as solar type stars. Therefore, they represent samples of Population I stars of constant age and comparable intrinsic chemical composition, suited for the study of processes linked with the stellar structure and evolution, and to fix lines or loci in several most important astrophysical diagrams. As a summary it can be concluded that open clusters allow to study a significant amount of astrophysical parameters and models from the global scale of the Milky Way down to processes in individual stars from the Pre-Main-Sequence to Post-AGB evolution. We therefore want to present our latest work concerning the accuracy of open cluster parameters, the search for chemically peculiar stars in galactic open clusters and the Large Magellanic Cloud, our broadband survey of open clusters, the investigation of a very young aggregate and the database for open clusters WEBDA.

[P20] Nikolov, G.; Atanasova, E.; Iliev, I. Kh.; Paunzen, E.; Barzova, I.
Spectroscopic orbit determination of two metal-weak dwarf stars: HD64491 and HD141851
Based on CCD high-resolution spectra radial velocity curves of HD64491 and HD141851 have been studied. Both stars are SB1 spectroscopic binaries with metal-weak characteristics. PHOEBE code was used to derive the spectroscopic orbit solutions. Following parameters have been calculated for HD64491: Porb = 187.9 days, e = 0.5, asini = 0.4 a.u., q = m2/m1 ≤ 0.6. For the other star HD141851 we obtained: Porb = 1073 days, e = 0.7, asini = 1.15 a.u., q = m2/m1 ≤ 0.5.

[P21/22] Paunzen, E.
WEBDA - A tool for CP research in open clusters
WEBDA is a site devoted to observational data on stars in stellar clusters in the Milky Way and the Magellanic Clouds. It is intended to provide a reliable image of the available data and knowledge on these objects and to offer a wide access to the existing observations for professional and amateur astronomers. The success of WEBDA is documented by the worldwide usage and the acknowledgements to it in the literature: more than 450 publications within the last seven years refer to WEBDA. It collects all published data for stars in open clusters that may be useful either to determine the star membership, or to study the stellar content and properties of the clusters. The database contents includes measurements in most photometric systems in which cluster stars have been observed, spectroscopic observations, astrometric data, various kinds of useful information, and an extensive bibliography. The latter includes the complete Budapest bibliography and its updates until 1994 (the last year of its maintenance) which is based on the Catalogue of Star Clusters and Associations (CSCA). The data are usually recorded in their original form, with an indication of the source, but also as averaged values or selected data when relevant. All data can be directly retrieved via http. The greatest effort has been spent in solving the identification problems raised by the definition of so many different numbering systems. There is an unique WEBDA number for each star within the individual open clusters and a special interface has been developed to query the cross-reference tables. Each new publication with its own numbering system will be transformed in the already existing one and objects not recorded before gets a consecutive number.

[P23] Pavlovski, K.; Southworth, J.; Tamajo, E.
Spectral disentangling of the metallic-lined binary system WW Aurigae
Spectral disentangling is a powerful new technique which enables separation of a time series of composite spectra into the spectra of individual component stars. This process is not compromised by blending, and also produces disentangled spectra with a much higher signal to noise than the individual composite spectra. The resulting spectra can be analysed in the same way as those obtained for single stars, but with the added advantage that the surface gravity can be directly and accurately measured if the binary system is eclipsing. Further constraints can also be put on the temperatures of the two stars using the results of the light curve analysis.

WW Aur is a doubled-lined and eclipsing binary system, so is an ideal target for the application of spectral disentangling. Both components show Am star characteristics. Recently, Southworth et al. (2005) studied the system both photometrically and spectroscopically, measuring the masses and radii of the components with accuracies of 0.4 and 0.6 percent, respectively. The properties of the system are now among the most accurately known for any stars beside Sun. The masses and radii match the predictions of theoretical evolutionary models only for a high overall metal abundance of 2.5 times the solar abundance.

In continuation of that study, we have reanalysed the 58 spectroscopic observations, from the INT at La Palma, and have obtained the separated spectra of the two components by disentangling. Our goal is to further improve the determination of the effective temperatures, and to study the chemical composition and Am star characteristics of both components. Our initial results are presented in this poster.

[P24] Petit, V.; Wade, G.A.; Drissen, L.; Montmerle, T.; Grosso, N., Menard, F.
On the X-ray emission and the incidence of magnetic field in massive stars of the Orion Nebula Cluster
Magnetic fields have been frequently proposed as a likely source of variability and confinement of the winds of massive stars. Recently, Stelzer et al. (2005) found significant X-ray emission from all massive stars in the Orion Nebula Cluster (ONC). Periodic rotational modulation in X-rays and other indicators suggested that there might be many magnetic B- and O-type stars in this star-forming region. We have carried out sensitive ESPaDOnS observations to search for direct evidence of such fields, detecting unambiguous Zeeman signatures in three objects. We also obtained dipole field upper limits for the remaining stars with a state-of-the-art Bayesian analysis, resulting in a precise magnetic characterisation of all ONC massive stars. This allows us to explore for the first time the connections between fields, winds and X-rays in a complete, co-eval and co-environmental sample of massive stars. These remarkable results bring forth new challenges for understanding the processes leading to X-ray emission in massive stars. We also expect to provide unique data regarding the incidence of magnetic fields in massive stars with which to confront models of magnetic field origin in neutron stars and magnetars, such as that proposed by Ferrario & Wickramasinghe (2006).

[P25] Pintado, O.
HgMn stars observed at CASLEO
We present the preliminary results of spectral analyses of the HgMn star HR4817. The abundance calculation is obtained comparing observed with synthetic spectra. The observed spectra were obtained with the bench echelle spectrograph at Complejo Astronómico El Leoncito. We compare the results with our previous analyses of the same star. The abundances are more accurate and we found elements we didn't find in our previous analyses.

[P26] Power, J.; Wade, G.A; Hanes, D.A.; Silvester, J.; Landstreet, J.D; Aurière, M.; and the TBL MuSiCoS Team
Physical, magnetic and rotational properties of a volume-limited sample of Ap/Bp stars
Using the Hipparos catalogues, the General Catalogue of Ap and Am Stars, and other literature sources, we conclude that there exist 57 bona fide magnetic Ap/Bp stars within 100 pc of the sun. Temperature, luminosity, and mass were determined for each of these stars using published photometry and energy distributions, photometric calibrations, and Hipparcos parallaxes. Using the MuSiCoS spectropolarimeter at Pic du Midi Observatory, Least-Squares Deconvolved (LSD) Stokes V profiles were obtained for 26 of the sample stars. These observations were used in combination with published data to refine periods, determine projected rotational velocities, and determine magnetic field strengths and geometries. The magnetic chemically peculiar stars comprise 1.5% (57 Ap/Bp stars out of 3904 intermediate mass stars) of all intermediate-mass stars within 100 parsecs of the sun. The masses of the Ap/Bp stars range from 1.5 to 6 Msun, with the probable peak of the fractional incidence distribution (as a function of mass) located between 3.3 and 3.6 Msun. Statistical distributions of measured properties, including rotational period, surface dipole field strength, rotational axis inclination and magnetic obliquity angle were analyzed. The rotational periods of the sample show a smooth distribution with a median of 3.0 days, and with an extended tail to very long periods. The histogram of obliquity angles shows a bimodal distribution about 0 and 90 degrees. The distribution of surface dipole field strengths exhibits a plateau at 2.5 kG, dropping off to higher and lower field strengths. The results obtained are consistent with those of Auriere et al. (2007), who report the absence of magnetic dipole fields in Ap stars weaker than about 300 G.

[P27] Sapar, A.; Aret, A.; Sapar, L.; Poolamäe, R.
Formulae for study of LID induced diffusion in CP star model atmospheres
The expression for LID acceleration in the inner layers of stellar atmosphere and deeper, where the diffusive approximation for radiative transfer holds, has been given. The equation of continuity and the equation of momentum transfer have been reduced to form, useful for making computations of evolutionary scenario of isotope segregation based on the model atmosphere.

[P28] Schröder, Ch.; Hubrig, S.; Schmitt, J.H.H.M.
Magnetic fields in X-ray emitting A-type stars
A common explanation for the observed X-ray emission of A-type stars is the presence of a hidden late-type companion. While this hypothesis can be shown to be correct in some cases, there is also evidence suggesting that low-mass companions cannot be the correct cause for the observed X-ray activity in all cases. Babel and Montmerle (1997) presented a theoretical framework to explain the X-ray emission for magnetic Ap/Bp stars, focussing on the A0p star IQ Aur. We test if this theoretical model is capable to explain the observed X-ray emissions. We present the observations of 13 A-type stars that have been associated with X-ray emission detected by ROSAT. To determine the mean longitudinal magnetic field strength we measured the circular polarization in the wings of the Balmer lines using FORS 1. Although the emission of those objects with magnetic fields fits the prediction of the Babel and Montmerle model, not all X-ray detections are related to the presence of a magnetic field. Additionally, the measured strengths of magnetic fields do not correlate with the X-ray luminosity and thus the magnetically confined wind shock model cannot explain the X-ray emission from all investigated stars.

[P29] Shulyak, D.; Kochukhov, O.; Khan, S.
Model atmospheres of magnetic CP stars: HD137509
We present the results of modeling the atmosphere of one of the extreme magnetic CP star HD137509, which has the mean surface magnetic field module of about 29 kG. Such a strong field, as well as clearly observed abundance peculiarities, make this star one of the most preferable target for testing our assumptions about the atmospheric structure of magnetic stars. The calculations presented are based on resent version of the LLmodels stellar model atmosphere code which accounts for full treatment of Zeeman splitting of spectral lines and polarized radiative transfer.

[P30] Simic, Z.; Dimitrijevic, M.S.; Popovic, L.C.; Dacic, M.; Kovacevic, A.; Sahal-Brechot, S.
On the Stark broadening of Mn II lines for Ap star conditions
In CP star atmospheres exist conditions where Stark widths are comparable and even larger than the thermal Doppler widths, so that the corresponding line broadening parameters are of importance for the CP star plasma investigations. Ionized manganeze lines are present in CP star spectra and the relevant line broadening data may be significant for their analysis and synthesis as well as for the modelling and consideration of subphotospheric layers. Recently, a disagreement of up to 5.7 times is found between experimental and calculated Stark widths and shifts of Mn II lines. In order to investigate the possible reasons, we performed more sophysticated calculations for six Mn II lines, by using the semiclassical perturbation theory. Calculations were also performed for ionized helium impact broadening in order to check if this contribution may improve the agreement between experiment and theory. Moreover, we made a detailed analysis of the influence of hfs splitting on the considered experimental results. Also, the obtained results have been applied to compare Doppler and Stark broadening contributions in CP star atmospheres.

[P31] Sousa, J.; Cunha, M.S.
Towards the understanding of radial velocity pulsation in roAp stars
High-resolution spectroscopic time series of rapidly oscillating Ap stars show evidence for a co-existence of standing and running waves in their atmospheric layers. With the purpose of understanding these observations we have carried out a theoretical analysis of the pulsations in the outermost layers of these stars, starting from the simplest possible model that still retains all important physical ingredients. In our analysis we considered an isothermal atmosphere in a plane-parallel approximation. Moreover we assumed that in the region considered the magnetic pressure is much larger than the gas pressure and, consequently, that the magnetoacoustic wave has decoupled into its acoustic and magnetic components. Using the analytical solutions for the velocity components appropriate to this model we estimate the velocity component parallel to the line of sight averaged over the visible stellar disk. Fitting the latter to a function of the form Acos(wt+phase), with w the oscillation frequency and t the time, we derive the amplitude A and the phase for our model as function of height in the atmosphere. Finally, we compare these results with corresponding amplitudes and phases published in the literature determined from the analysis of high-resolution spectroscopic data of roAp stars.

[P32] Stateva, I.; Budaj, J.; Belcheva, M; Iliev, I.; Barzova, I.
Chemical abundances study of three Am stars HD159560, HD196544 and HD155375
The main goal of this paper is to continue a systematic abundance analysis of a sample of 12 Am binaries in order to search for possible abundance anomalies driven by tidal interaction in these binary For such systems the "tidal mixing + stabilization" hypothesis of Budaj (1998) predicts that the tidally driven meridional circulation might successfully compete with diffusion processes and rotationally composition of the first 9 of these stars and basic stellar properties were determined. A synthetic spectrum analysis of CCD observations in the spectral region 6400-6500 ÅÅ of the last 3 stars, HD 155375, HD 159560 and HD 196544, was carried out. All stars show typical Am characteristics. We also searched for possible observable abundance anomalies driven by tidal interaction in these binary systems. We have identified possible dependences of the abundance anomalies of Ca and Fe, as well as the [Ca/Fe] ratio, on the effective temperature, vsini and eccentricity.

[P33] Stütz, Ch.; Nesvacil, N.; Fossati, L.; Shulyak, D.
On the quality of stellar atmosphere parameters and abundances derived from spectroscopy
Abundance analyses are usually performed by hand. The existing semi-automatic software packages mostly are strongly dependent on a starting or fixed set of fundamental parameters and the set of lines provided by the researcher. Furthermore the implemented iterative processs of fitting certain lines or regions of a star's spectrum, often ignore the parameters physical meaning. Thus, the accuracy of the derived results and moreover the comparibility of different investigations are in many cases left to the researchers judgement. However, several attempts to study how uncertainties in single fundamental or line parameters translate to the precision of abundance determination have been successfully conducted. We started to investigate the combined effect of variations in effective temperature, surface gravity, microturbulence, line blending, metallicity (i.e. abundance pattern) together with the number of atomic lines used. Our aim is to be able to make quantitative statements on this general uncertainty in abundance analysis and to define a way to automatize determination of fundamental parameters and element abundances while: providing a tracable measure of accuracy for the results; being not restricted to a certain instrument, resolution or object; minimizing the effort of preparation.

[P34] Stütz, Ch.; Paunzen, E.
On the λ Bootis spectroscopic binary hypothesis
It is still a matter of debate whether the group of λ Bootis stars have been homogeneously defined. A widely discussed working hypothesis postulates that two apparent, solar-abundant stars of an undetected spectroscopic binary system mimic a single metal-weak spectrum thus preventing any reliable analysis of the group characteristics. Using the newest available stellar atmosphere models and synthesis codes, we investigate whether the proposed spectroscopic binary model can explain the observed abundance pattern as well photometric metallicity indices and what the percentage of undetected spectroscopic binary systems is. As first step we synthesized 105 hypothetical binary systems in the relevant astrophysical parameter range. These models were used to derive photometric indices. As a test, values were generated for single stellar atmospheres, Vega and two typical λ Bootis stars, HD 107233 and HD 204041.

[P35] Thiam, M.; Wade, G.A.; LeBlanc, F.; Khalack, V.R.
Search for abundance stratification in the atmospheres of HgMn stars
Photospheric abundance determinations for several HgMn stars were undertaken using archival ESO-UVES spectra. Unblended lines in the visible region of the spectrum of the elements Ti, Cr, Mn and Fe were used to obtain their abundance and to search for the presence of abundance stratification as a function of optical depth. Using spectrum synthesis, the abundance associated with each line was computed and analysed as a function of the line core formation depth to evaluate the vertical stratification of each element. Results are reported for two stars: HD 178065 and HD 175640. Of the elements studied, only Mn shows signs of abundance stratification.

[P36] Wahlgren, G.; Leckrone, D.S.
Heavy elements in the hot-Am star HR3383
We present results from our on-going analysis of the ultraviolet spectrum of the sharp-lined hot-Am star HR 3383 (HD 72660). The main focus of the investigation is the identification and abundance analysis of post iron-group elements using high-resolution spectra obtained with the Hubble Space Telescope. Although the ultraviolet spectrum of HR 3383 is crowded with lines of Fe II, which hinders line identification and analysis, spectral lines from many heavy element species can be identified. Of particular note are the presence of lines from the heaviest stable elements, for which abundances will be useful for testing ideas on atmospheric abundance enhancement mechanisms for Am and HgMn stars.

[P37] Yudin, R.; Pogodin, M.; Hubrig, S.; Schöller, M.
Magnetic fields in Herbig Ae stars
We present the results of our latest studies of the circumstellar magnetic fields in Herbig Ae stars and briefly discuss the cause of the failure of another recent study by our colleagues to confirm the Zeeman features on our spectra.

[P38] Zverko, J.; Žižňovský, J.; Mikulášek, Z.; Iliev, I.Kh.
53 Aurigae revisited: a B9Mn + F0m composite spectrum
53 Aur known as a CP star of various peculiarity types is revisited. Based on high-resolution high S/N CCD spectra the spectrum of the double star 53 Aur was disentangled to a B9-Mn and an F0m components.