Review/Introduction Talk: 30 + 10 min

Contributed Talk: 15 + 5 min

CP#AP Workshop Schedule (as at Aug 31st)

The lecturer (in alphabetic order) is given in bold style.

Alecian, E.; Wade, G.A.; Catala, C.; Folsom, C.; Grunhut, J.; Donati, J.-F.; Petit, P.; Bagnulo, S.; Marsden, S.C.; Landstreet, J.D.; Boehm, T.; Bouret, J.-C.; Silvester, J.
Magnetism in pre-main sequence intermediate-mass stars and the fossil field hypothesis
Today, one of the greatest challenges concerning the Ap/Bp stars is to understand the origin of their slow rotation and their magnetic fields. The favoured hypothesis for the latter is the fossil field, which proposes that the magnetic fields observed in Ap/Bp stars are relics of the magnetic fields of their parental molecular clouds. This hypothesis implies that these fields subsist throughout the different evolutionary phases, from the contraction of the molecular clouds to the main sequence phase, and in particular during the pre-main sequence phase. The existence of magnetic fields at the pre-main sequence phase is also required to explain the slow rotation of Ap/Bp stars (e.g. Stepien 2000, Stepien & Landstreet 2002). However, until recently, essentially no information was available about the magnetic properties of intermediate-mass pre-main sequence stars, the so-called Herbig Ae/Be stars. The new high-resolution spectropolarimeter ESPaDOnS, installed in 2005 at the Canada-France-Hawaii telescope, provided the capability necessary to perform surveys of the Herbig Ae/Be stars in order to investigate their magnetism and rotation. These investigations have resulted in the detection and/or confirmation of magnetic fields in 8 Herbig Ae/Be stars, ranging in mass from 1.5 to nearly 15 solar masses. In this talk I will present the results of our survey, as well as their implications for the origin and evolution of the magnetic fields and rotation

Alecian, G.; Stift, M.J.
Stratification of elements in magnetic Ap stars
We present recent modelling of equilibrium element stratifications (i.e. stratifications such that the particle flux becomes zero) in CP star atmospheres due to atomic diffusion. We consider the distributions of some metals in plan-parallel atmospheres, including Fe, in the presence of magnetic fields with several strengths and inclinations, and for several effective temperatures. The effects of element stratifications on continuous opacities are also discussed. We compare our calculations to empirical stratifications derived from CP star spectra.

Sapar, A.; Aret, A.; Sapar, L.; Poolamäe, R.
Segregation of isotopes of heavy metals due to light-induced drift: results and problems
Almost two decades ago Atutov and Shalagin proposed light-induced drift (LID) as a physically well understandable additional mechanism for explanation of diffusion of chemical elements and their isotopes in the envelopes and atmospheres of quiescent CP stars. We generalized the theory of LID and applied it to diffusion of heavy elements and their isotopes in atmospheres of CP stars. Diffusional segregation of isotopes of chemical elements is based on the equations of continuity and of the diffusion velocity. Computations of the evolutionary model atmosphere sequences have been made using a FORTRAN program SMART, composed by the authors. The short, handy and user-friendly program is meant for modeling of stellar atmospheres, for study of physical processes in them and for computation of stellar spectra.

Arlt, R.
Generation and stability of magnetic fields in CP stars
The presentation will review dynamo mechanisms relevant to CP stars and their applicability for explaining the magnetic fields observed. Turbulent as well as laminar dynamos are shown. The second part of the talk will focus on the stability of various types of magnetic fields in radiative environments, such as the envelopes of CP stars. The importance of a combined study of an early dynamo and the long-term stability of the generated fields is foreseen.

Aurière, M.; Wade, G.A., Lignìeres F.; Landstreet, J.D.; Donati, J.-F., Hui Bon Hoa, A.; Petit, P.; Roudier, T.; Theado, S.; Iliev, I.
Weak magnetic fields in CP stars
We present the first results of a magnetic survey of main sequence A and late B stars with NARVAL, the new generation spectropolarimeter available at Telescope Bernard Lyot at Pic du Midi Observatory since december 2006. We observed 3 HgMn stars, 13 Am stars and the only Ap star for which no Zeeman detection was obtained with MuSiCoS. If we combine our results with those of our previous survey of weak magnetic fields in spectroscopically selected Ap/Bp stars we get the following situation: - Ap/Bp stars: all these stars appear to host a detectable magnetic field. A threshold dipolar magnetic field of 300 G appears to exist, below which fields are very rare and perhaps altogether absent. - Am and HgMn stars: no magnetic field is detected up to now for the 16 observed stars. An accuracy down to 0.5 G (respectively 1 G) is reached on longitudinal magnetic field measurements for Am (respectively HgMn) stars. We propose a possible interpretation of the observed threshold field which naturally explains the magnetic dichotomy: There exists a critical field strength above which stable magnetic configurations exist and below which any large scale field configuration is destroyed by some instability. This scenario can easily produce a population of stars in which a majority display no evidence of magnetic fields, and in which a minority display relatively strong, organised fields. Those stars in which magnetic fields are retained are the Ap/Bp stars.

Bagnulo, S.; Fossati, L.; Landstreet, J.D.; Wade, G.A.
Observations of magnetic fields of Ap stars: the status of the art
Chemically peculiar stars of the upper main sequence are the most popular targets for the detection and modelling of stellar magnetic fields. Here we will critically review the relevant observational techniques, and we will make a summary of the measurements carried out so far in CP stars. We will review the modelling techniques, and finally we will discuss which physical questions the observational/modelling works, that are nowadays routinely carried out, may help to address.

Bischof, K.; Stift, M.J.
Modeling stellar atmospheres with full Zeeman treatment
In the atmospheres of magnetic chemically peculiar (CP) stars non-homogeneous distributions (vertical and horizontal) of various chemical elements are found, a fact which is interpreted as resulting from radiative levitation and gravitational settling, modified by the field lines of a large-scale magnetic field. In order to model these diffusion processes self consistently, one cannot rely on standard atmospheric models (ATLAS-like) for these stars, since Zeeman splitting leads to enhanced line opacity and increased radiative accelerations, and since the magnetic pressure alters the net gravity. Therefore a new code for magnetic stellar atmospheres has been developed, based on a polarised line synthesis code and ATLAS12 continuous opacities. We shall give a brief overview of the input physics and also on software engineering issues, including efficient strategies for parallel processing. Our findings will be compared with the results of other groups.

Braithwaite, J.
Fossil fields and MHD instability in rotating stars
It has been shown numerically that an arbitrary magnetic field in a star can organise itself into a stable configuration which is approximately axisymmetric and appears dipolar on the surface. The conditions under which this either happens or does not happen are explored, as well as the effect of rotation on the possible configurations. The existence of non-axisymmetric equilibria with, for instance, a strong quadrupole or octupole component, is predicted.

Cowley, C.; Hubrig, S.; Castelli, F.
Isotopic Anomalies in CP Stars: Helium, Mercury, Platinum, and Calcium
We review the classical observational results for isotopic abundance variations for several elements in CP stars. We concentrate on the "newest" anomaly, in calcium. The cosmically very rare isotope, Ca-48 can rival and even dominate the more common, alpha nuclide, Ca-40. Relevant examples are found in the hot, not-magnetic HgMn stars, and the field horizontal-branch star, Feige 86. The calcium anomaly is also present in cool, magnetic stars, including the notorious HD 101065, Przybylski's star.

Dworetsky, M.; Dyer, A.
Strontium and Yttrium in HgMn Stars
We have undertaken a new study of these elements in the Smith & Dworetsky (1993) sample of HgMn stars using optical spectra from Lick Observatory, the Anglo-Australian Telescope, and ESO. Strong overabundances of Sr (c. 2.5 dex) tend to be concentrated in the HgMn stars at lower effective temperatures around 11000 K. We find that there are definitely several HgMn stars at or above 13000 K with considerable sub-solar abundances of Sr. Yttrium is clearly overabundant by c. 3-4 dex in many HgMn stars, but it is difficult to detect in the optical spectra of the stars of highest effective temperature even if overabundant.

Elkin, V.; Kurtz, D.; Mathys, M.
VLT observations of rapid radial velocity variations in roAp stars
We will review of time resolved high resolution spectroscopy with ESO UVES VLT for sample of roAp stars. Amplitudes and phases and other pulsation properties obtained from different chemical elements will be discussed.

Folsom, C.P.; Wade, G.A.; Kochukhov, O.; Alecian, E.; Catala, C.; Bagnulo, S.; Landstreet, J.D.; Hanes, D.A.
Magnetic, Chemical and Rotational Properties of the Herbig Ae/Be Binary System HD 72106
Recently, strong globally ordered magnetic fields have been detected in some Herbig Ae and Be (HAeBe) stars, suggesting a possible evolutionary connection to main sequence magnetic chemically peculiar Ap and Bp stars. We have undertaken a detailed study of the binary system HD 72106, which contains a magnetic B9 primary and a HAeBe secondary, using the ESPaDOnS spectropolarimeter mounted on the CFHT. A careful analysis of the very young primary reveals that it has an approximately dipolar magnetic field geometry, strong chemical peculiarities, and strong surface chemical abundance inhomogeneities. Thus the primary is very similar to an Ap/Bp star despite having completed less then 1.5% of its main sequence life, and possibly still being on the pre-main sequence. In contrast, a similar analysis of the secondary reveals solar chemical abundances and no magnetic field.

Fossati, L.; Bagnulo, S.; Monier, M.; Khan, S.A.; Kochukhov, O.; Landstreet, J.; Wade, G.; Weiss, W.
Chemical evolution of A- and B-type stars in open clusters
We have decided to address the problem of how abundances and peculiarities change during main sequence evolution. We have setup a program to measure the atmospheric abundance patterns from tens of A-type star members of clusters of different ages, and compare the results with theory predictions. We dedicate this first work to the Am stars of the Praesepe cluster (log t = 8.85), searching for magnetic fields in these objects and discussing the differences between normal A-type stars and Am stars in the cluster. We have obtained spectra for eight Am stars, two normal A-type stars and one Blue Straggler, that are probable members of the Praesepe cluster. For all of these stars we have determined fundamental parameters and photospheric abundances for a large number of chemical elements. For seven stars we also obtained spectra in circular polarization and applied the LSD technique to measure the mean longitudinal magnetic field. We have found good agreement between abundance predictions of diffusion models and measured abundances, excpet for Na and S. Li appears to be overabundant in three stars of our sample. No magnetic field was detected in any of the analysed stars.

Gerth, E.; Glagolevskij, Yu.V.
Ten years magnetic modelling of stars by field sources - a review
Since Babcock's epoch-making work half a century ago an enormous quantity of observational data on magnetic stars has been compiled, waiting for analysis and interpretation. Arranging the data in phase curves, one could hope to discover at least a rough topographic structure of the magnetic surface field by an inverse procedure. This has been done by Khokhlova, Piskunov, Kochukhov. Bagnulo et al. modelled the surface field by spherical harmonics with the poles as parameters. Ten years ago Glagolevskij and Gerth proposed a modelling method to construct the magnetic field out of its sources and vortices by a straightforward calculation. After a theorem of the potential theory, the sources and vortices are the constituents of any vector field. In analogy to electric fields there were formally introduced "magnetic charges", which allow to use a standard algorithm for the point-like source, relating to a minimum of physically significant parameters. The sources can be positioned inside and/or outside the star, filling by their superposed fields the entire space -- the magneto-sensitive atmosphere included. The program has been developed to a useful multivalent tool for controlling the inverse derivation of the surface field but, above all, to construct the field on a synthetic way, hereby fitting the calculation to the observational facts.

Griffin, E.
Ap versus normal stars
Appreciation of the significance of any spectrum abnormalities must perforce be based upon comparisons with a "normal" one. However, "normal" A-type stars are proving remarkably elusive; meetings focussing on A-type stars have repeatedly addressed the issue of normal versus abnormal A stars without appearing to reach a fully satisfactory solution. Such seeming insolubility could indicate that the problem has been tackled from the wrong end. As an introduction to the Workshop, the paper discusses some implications of inverting the problem, and will encourage other presentations and discussions to take this model into consideration.

Gruberbauer, M.; Saio, H.
Testing the theory of roAp stars: The MOST observations of gamma Equleii
In 2004, the MOST satellite observed the roAp star gamma Equ continuously for 19 days, delivering an unprecedented photometric coverage of its pulsations. The data analysis led to a set of 5 p-mode frequencies. Mode identification was explored by fitting these frequencies to the latest generation of roAp magnetic models computed by Hideyuki Saio. A possible explanation for amplitude modulation previously observed in gamma Equ (and other roAp stars) will also be discussed.

Hubrig, S. et al.
Magnetic fields in massive stars
We will review the recent discoveries of magnetic fields in different types of massive stars and briefly discuss strategies for spectropolarimetric observations to be carried out in the future.

Iliev, I.Kh.; Budaj, J.
Am stars in binary systems
Tidally induced meridional circulation that can exist in the atmospheres of Am stars members of binary systems is discussed. It is concluded that tides can successfully compete with rotation, and radiatively driven diffusion. As a result abundance pattern of Am stars in binary systems depends on the orbital elements as well. Am peculiarities are expected to be more pronounced in binaries with larger eccentricities, and also at longer orbital periods.

Janík, J.; Mikulášek, Z.; Szász, G.; Zejda, M.; Zverko, J.; Zvěřina, P., Žižňovský, J.
Progress in on-line photometric database of mCP stars
The On-line Database of Photometric Observations of mCP Stars is available since about one and a half year. Beside the day-to-day maintenance, new data from the ASAS2/ASAS3 project is included now in the database. Due to changes in the database scripts, it is possible to calculate and display phase curves for individual stars. Each star is analyzed using the PCA method. Furthermore, an interface between the database and advanced scripts for data processing is in preparation. This interface will be available for users after its publication. Investigators interested in a detailed study of stars included in our database are welcome.

Kamp, I.; Martinez Galarza, J.R.; Paunzen, E.; Su, K.Y.L.; Gásp, A.; Rieke, G.H.
λ Bootis stars: Current status and new insights from Spitzer
The group of λ Bootis type stars comprises late B- to early F-type, Population I objects which are basically metal weak, in particular the Fe group elements, but with the clear exception of C, N, O and S. We present a spectroscopical definition for the group membership by using the light element versus metal abundance pattern. One of the current explanations for the λ Bootis peculiarity is the accretion of interstellar material as the star travels through a diffuse interstellar cloud. We will review this hypothesis in the context of ESO high resolution spectra and Spitzer imaging and photometry. The Na I D lines provide simultaneously stellar abundances and physical properties of interstellar material along the line of sight. The new Spitzer results shed light on the presence of dust around theses stars, its composition and geometric distribution.

Khan, S.
Model atmospheres of magnetic and chemically peculiar stars
The recent results of the theoretical analysis of the model atmospheres of magnetic and chemically peculiar stars are presented. All the calculations are based on the direct opacity sampling technique, and account for the anomalous Zeeman effect and polarized radiation transfer (i.e. full Zeeman treatment). The study includes analyses on the model atmosphere structure, energy distribution, photometric colors, etc., and investigates the role of the magnetic field (its strength and inclination) as well as different chemical compositions (abundance patterns) on the stellar model atmospheres.

Kochukhov, O.
Magnetic fields, spots and weather in chemically peculiar stars
New observational techniques and novel modelling methods lead to dramatic breakthroughs in our understanding of the interplay between the surface magnetism, atomic diffusion and atmospheric dynamics in chemically peculiar stars. Magnetic Doppler images derived from the four Stokes parameter observations of Ap stars reveal amazing complexity of the field topologies. Abundance Doppler mapping has been perfected to the level where self-consistent distributions of more than ten different elements can be deduced in one star. At the same time, the vertical dimension of the Ap-star atmospheres is resolved with the help of stratification analysis and using magnetoacoustic pulsations as atmospheric probes. The inferred chemical spot structures are diverse and do not always trace underlying magnetic geometry. Moreover, horizontal chemical inhomogeneities are discovered in non-magnetic CP stars and evolving chemical spot geometry is observed for the first time in the bright mercury-manganese star alpha And. These results suggest that, in addition to magnetic fields, another important, non-magnetic, structure formation mechanism acts in CP stars.

Krtička, J.; Mikulášek, Z.; Zverko, J.; Žižňovský, Z.
Rotationally modulated photometric variations of mCP stars - theoretical aspects
We study the theoretical aspects of the light variability of chemically peculiar stars. The star HD 37776 serves us as a test case for our understanding of the light variability. We are able to predict the light curve of this star from the known elemental surface distribution. We show that the light variability of this star is mainly due to inhomogeneous surface distribution of silicon and helium. We discuss the role of other elements, magnetic field, and NLTE effects for the modelling of light variability of chemically peculiar stars.

Kudryavtsev, D.O.; Romanyuk, I.I.
Magnetic CP stars with large depression in continuum
Spectropolarimetric observations of more than 100 CP stars have been carried out at the 6m telescope with the aim of searching for the presence of stellar magnetic fields. The stars selected for investigation were CP stars known to have strong anomalies in the wavelength region of the continuum flux depression around λ 5200 Å. Magnetic fields have been detected in 80 stars. Different correlations between magnetic fields and anomalies in the energy distribution in the continua of the stars have been considered. We have found a weak increase of Δ a values with rotation period for stars with the same effective temperatures and a weak decrease of the average longitudinal magnetic field with time.

Landstreet, J.D.; Bagnulo, S.; Andretta, V.; Fossati, L.; Mason, E.; Silaj, J.; Wade, G.A.
Magnetic field evolution inferred from fields of open cluster stars
Little is known observationally about evolution during the main sequence phase of magnetic field strength and structure, or of chemical peculiarities, in magnetic Ap stars. This is mainly due to the difficulty of obtaining accurate ages for field Ap stars. To improve this situation, we have been carrying out a survey of possible magnetic Ap stars in open clusters, for which accurate ages are available. The data so far obtained suggest that fields in stars of more than 3 Mo decline strongly with a time-scale of about 30 Myr, while in lower mass Ap stars the fields do not change much even in more than 100 Myr. In a later phase of this study we will also explore the evolution of atmospheric chemistry with age.

Lüftinger, T.; Kochukhov, O.; Piskunov, N.; Ryabchikova, T.; Weiss, W.W.; Ilyin, I.
3D atmospheric structure of the prototypical roAp star HD 24712 (HR1217)
The first analysis of the structure of the surface magnetic field of a rapidly oscillating Ap (roAp) star is presented. We deduce information about magnetic field geometry and abundance distributions of a number of chemical elements on the surface of the prototypical roAp star HD 24712 using INVERS10, an elaborate magnetic Doppler Imaging (MDI) code (Piskunov et al. 2002, Kochukhov et al. 2002), which allows to reconstruct simultaneously and consistently the magnetic field geometry and elemental abundance distributions on a stellar surface. Inverting rotationally modulated time series spectra in Stokes I and V obtained with the NOT/SOFIN spectropolarimeter, we recover surface abundance structures of sixteen different chemical elements, respectively ions, including Mg, Ca, Sc, Ti, Cr, Fe, Co, Ni, Y, La, Ce, Pr, Nd, Gd, Tb, and Dy. Our analysis reveal a clear dipolar structure of the stellar magnetic field and surprising and unexpected correlations of the various elemental surface abundance structures to this field geometry. We relate our results to high time resolved spectroscopic data obtained with the VLT/UVES, to space quality photometric data obtained with the MOST satellite and to recent theoretical investigations by Cunha (2006), which gives rise to the possibilty. to trace magnetoacoustic effects in the atmosphere of this prototypical pulsating magnetic star. Stratification analysis at phases of both magnetic extrema and our analysis of magnetoacoustic pulsations enable us to unclose the vertical dimension in the atmosphere of HD 24712

Maitzen, H.M.; Paunzen, E.; Netopil, M.
What to expect from a census of Ap stars in open clusters in the Galaxy and abroad?
Since 110 years the group of peculiar stars of the upper main sequence exhibiting strong dipole-like magnetic fields is under investigation, but yet no consistent and conclusive scenario of their formation has been worked out. The wealth of their atmospheric phenomenology has motivated a significant strive by researchers to get insight into the specific conditions of stratified atmospheres giving rise to very colourful elemental abundances and distributions on the stellar surface. While those fascinating investigations necessarily have concentrated on stars in the vicinity of the solar system, the question which environmental conditions favour or suppress the formation of Ap-stars has to be tackled by research in more remote galactic regions, even in stellar systems of the Local Group (preferentially the Magellanic Clouds). This is so, because the role of metallicity is to be checked for, as well as the presence of a pervasive magnetic field in the stellar systems. It is clear that the appearance of Ap-stars at such distances can be traced only by an observational criterion which is based on a characteristic broad band feature in their spectral energy distribution. Since three decades the flux depression feature around 520 nm sampled by the Da-photometry has been used to identify Ap-stars not only in the galactic field, but especially also in open clusters, even in the LMC. So far 80 galactic open clusters and 4 in the LMC have been investigated for the presence of peculiar stars. Up to 1kpc distance from the Sun photoelectric photometry was used, but with the advent of the CCD technique significantly larger distances could be achieved. The performance of both methods has not exhibited significant systematic differences. An interesting result of this undertaking is the tendency of Ap-stars to appear more frequently in smaller open clusters: those with Trumpler classification "p" show at least 22 times the density of Ap-stars per cubic parsec compared to clusters with classification "r". This brings about the question whether different densities in open clusters may have played a significant role in the formation of Ap-stars. A hint to this could be found in the suggestion by W.P.Bidelman from the year 2002 that those stars form as a result of close binary mergers. We would like to propose a modification to this scenario in the sense that these mergings (or "near-mergings") should occur in the very early phases of star formation in a cluster and that the probability of near proto-stellar encounters should naturally be greater in aggregates with higher density. It is our feeling that the oblique rotator situation can be managed easier by the close encounter of two protostars in a crowded protostar cluster than by a single star alone.

Mathys, G.
Extremely slowly rotating magnetic Ap stars: recent results
Analysis of continued observations in unpolarised light and in circular polarisation of magnetic Ap stars with resolved magnetically split lines with rotation periods of several years revealed correlations between the properties of their magnetic fields and their rotation period that had not been identified so far. The implications of these newly found correlations will be briefly discussed.

Michaud, G.
HB stars as AmFm/HgMn stars
Recent observations and models for HB stars are briefly described and compared to models for AmFm stars. The limitations of those models are emphasized by a comparison to observations and models for HgMn stars.

Mikulášek, Z.; Krtička, J.; Graf, T.; Zverko, J.; Žižňovský, J.; Janík, J.
Rotationally modulated photometric variations of mCP stars - observational aspects
We present further results of our phenomenological analysis of general properties of light curves (LCs) of 87 magnetic chemically peculiar stars based on more than 57 thousands uvby and Hp observations taken from the "On-line database of photometric observations of mCP stars". Now we have concentrated to study of relations of forms of LCs in various colours for all stars of the set. Particularly, we discuss attributes of more or less "photometrically simply behaving" mCP stars with similar LCs in all colours. For these stars we expect that only limited number of dominating mechanisms of mCPs' variability is operating.

Nesvacil, N.; Ryabchikova, T.; Kochukhov, O.; Weiss, W.W.
Chemical Stratification in roAp stars: 10 Aquilae
We will present the results of our analysis of the vertical element stratification in the atmosphere of the roAp star 10 Aquilae (HD 176232). Using high resolution observations (R~100 000) obtained with the ESO-VLT spectropgraph UVES and state of the art model atmosphere and spectral synthesis codes we analysed the inhomogeneous vertical distribution of Fe,Cr,Si,Ca,Mg and Sr. Abundances for 29 other species were determined additionally. We will discuss the derived vertical abundance map of the star's atmosphere and compare our findings to other studies of (ro)Ap stars.

North, P.; Babel, J.; Erspamer, D.
Evolution of Ap stars determined from intelligent designs
The many peculiarities of Ap stars (not only chemical ones, but also magnetic field and slow rotation) may vary during the evolution of these stars on the main sequence. I review here the clever programmes designed since thirty years to find evidence for such an evolution, as well as the results obtained so far. Some additional data on surface magnetic fields are presented here as well.

Obbrugger, M.; Lüftinger, T.; Kochukhov, O.; Nesvacil, N.; Weiss, W.W.
Multi-element Doppler Imaging of the Ap star HD 3980
We present first results of the ongoing analysis of the inhomogeneous elemental surface distribution in the lithium rich Ap star HD 3980. We applied the Doppler imaging inversion code INVERS12 to derive surface maps of e.g., Fe, Li, Pr. For this work high-resolution time-series observations obtained with the VLT/UVES spectrograph were used.

Ryabchikova, T.
Abundance structure of the atmospheres of magnetic CP stars
A review of the recent results on abundance and stratification analysis of the magnetic CP stars is presented. It includes a brief description of the methods as well as a comparison between the element distributions derived from the observations and provided by the self-consistent diffusion model atmosphere calculations. He and Ca isotopic separation in the atmospheres of CP stars are considered. An importance of the stratification analysis for the study of pulsations in roAp atmospheres is emphasized. Finally, I discuss briefly recently published identifications of the unstable elements in spectra of Przybylski's star (HD 101065) and HD 965.

Sachkov, M.; Kochukhov, O.; Ryabchikova, T.; Leone, F.; Bagnulo, S.; Weiss, W.W.
Spectroscopic monitoring of roAp star 10 Aql
We present the analysis of spectroscopic time-series observations of the roAp star 10 Aql. Observations were carried out with the UVES spectrograph on July 03, 09, 15, 17, and 24, 2007 and with the SARG spectrograph on July 14-16, 2007 simultaneously with the MOST mini-satellite photometry. All these data were analysed for radial velocity (RV) variations. In total 1000 spectral lines were measured with the centre-of-gravity technique. About 150 lines reveal clear pulsation signal. Time-series analysis of the spectroscopic data gives four frequencies. Three highest amplitude frequencies in spectroscopy coincide with the photometric ones. Phase-amplitude diagrams created for the lines of different elements/ions show that atmospheric pulsations may be represented by a superposition of the standing and running wave components, similar to other roAp stars. The highest RV amplitudes 200 -- 300 m/s were measured for the inner core of Hα and for Sm II and Tb III lines. We discover ≈0.5 period phase jump in the RV measurements across the Nd III line profiles of 10 Aql. This indicates the presence of the pulsation node in stellar atmosphere. The phase jump occurs at nearly the same atmospheric layers for the two main frequencies. There are no rotational modulation in the average spectra for the 6 different nights we analysed.

Schnell, A.
History of CP stars
Some introductory remarks about the historical development of the task of chemically peculiar stars are given.

Shibahashi, H.
The roAp phenomenon - many unsolved issues
Many issues have arisen with the increase of observations of roAp stars. To solve them, the influence of magnetic fields and chemical peculiarity must be taken into account. I will discuss the wave propagation in a stratified plane atmosphere with magnetic fields as fundamental basis for understanding of the roAp phenomenon. Also I will discuss the issue on the critical cut-off frequency. After then, I will discuss the line-profile variation and the effect of the non-greyness of the atmosphere on the oscillations.

Silvester, J.; Wade, G.A.; Landstreet, J.D.; Kochukhov, O.; Bagnulo, S.
Magnetic Doppler Imaging of Ap stars
We will introduce a project which exploits the unique polarimetric capabilities of ESPaDOnS to obtain high signal-to-noise ratio, high resolution, phase-resolved spectra of a selected sample of magnetic Ap stars in all 4 Stokes parameters. The resulting datasets will be used to construct detailed, assumption-free maps of the vector magnetic fields and chemical abundance structures in the photospheres of these stars using Magnetic Doppler Imaging. Such maps represent a crucial step toward understanding the origin and evolution of magnetic fields in upper-main sequence stars, and for constraining the influence of these fields on the chemical separation and mixing processes (e.g. diffusion, convection, mass loss) whose effects dominate the spectra of Ap stars.

Stepięń, K.
Effective Temperatures of Magnetic Ap stars
New determinations of effective temperatures of over 20 magnetic Ap stars are presented. They are based on fits of metal enhanced model atmospheres, computed by R. Kurucz, to full spectral energy distributions (UV from IUE plus visual from literature) of the stars. Improved calibrations of Strömgren photometric indices in terms of effective temperature and bolometric corrections are derived.

Stift, M.
Paschen is partially Back
Following earlier work by Mathys, the transition between the Zeeman and the Paschen-Back regime, the so called partial (or incomplete) Paschen-Back regime, is discussed in some detail. Multiplets of several elements have been investigated for interesting splittings and special diagnostic potential. Full Stokes spectra have been modelled for various oblique rotator models; they often show quite exotic behaviour. Finally a few words will be lost on software issues in the treatment of the partial Paschen-Back effect.

Takeda, Y.; Kawanomoto, S.; Ohishi, N.
Rotational feature of Vega and its impact on abundance determinations
Although it seems almost established that Vega is actually rotating rapidly and that its apparent sharp-line nature is because of being seen pole-on, any consensus has not yet been accomplished about how fast it is rotating; e.g., published results implied from the profile analyses of a few lines (Gulliver et al. 1994; Hill et al. 2004) and those from recent interferometric observations (Peterson et al. 2006; Aufdenberg et al. 2006) show appreciable discrepancies. We therefore tried to establish Vega's absolute rotational velocity (ve) separated from the inclination angle (i) by extensively studying the profiles of a large number (about 200) of weak lines, since their characteristic shapes may contain information of rotation-induced gravity darkening, while invoking the very high S/N (~1000-3000) and high-resolution (R~100000) spectrum data we have recently published (Takeda et al. 2007). Having restricted the freedom of the parameters from the requirements of spectral energy distribution, we concluded by comparing the observed and theoretical line profiles that ve = 175 km/s (with i=7deg) is the best solution. It was also found that the abundances derived from lines showing peculiar flat-bottom shapes (e,g., Fe I lines) tend to be overestimated by up to 0.2 dex when the conventional method of analysis is applied by using classical model atmospheres, though this effect is less significant for lines showing normal profiles (e.g., high-excitation Fe II lines).

Vick, M.; Michaud, G.
The Effects of Mass Loss on the Evolution of Chemical Abundances in Fm Stars
This is a continuation of the Montreal stellar model development project (Richard et al., 2001 and references therein). We have modified a stellar evolution code that self consistently calculates particle transport in order to introduce the effects of mass loss. By including homogenous mass loss in self-consistent evolutionary models we determine that mass loss rates similar to the one measured on the surface of the Sun can effectively reduce the predicted surface abundance anomalies from purely diffusive models of Fm stars (Turcotte et al., 1998) to the observed levels. By comparing our models with the star t UMa we find that observations can be reproduced. We also find that the effects of mass loss can be distinguished from the ones encountered with turbulence, but are nevertheless able to explain the particularities of the AmFm phenomenon

Wade, G.A.; Catala, C.; Alecian, E.; Bagnulo, S.; Folsom, C.P.; Landstreet, J.D.
General magnetic properties of Herbig Ae/Be stars
The discovery of magnetic fields in a small number (<10) of Herbig Ae/Be stars (see talks by E. Alecian and C. Folsom) has required that we survey a much larger sample of stars. From our FORS1 and ESPaDOnS investigations, we have accumulated ~140 magnetic measurements of ~75 Herbig stars. These data can be used to evaluate the general magnetic properties of these objects. Using a Monte Carlo approach, we have performed statistical comparisons of the observed longitudinal fields and LSD Stokes V profiles of the Herbig stars in which no magnetic field was detected with a variety of field models. A byproduct of this procedure, for stars observed with ESPaDOnS, is our ability to place realistic upper limits on undetected dipole fields which may be present in individual stars. This talk briefly reports the results of the statistical modeling, as well as field upper limits for individual stars of particular interest.

Wahlgren, G.
Weak emission lines and chemically peculiar stars
We review observations made to date of weak emission lines (WELs) in mid to late B-type main-sequence stars, and discuss the ideas put forward to explain their origin. The presence and nature of WELs is dependent upon chemical abundance, thereby making them a useful tool for developing models of stellar atmospheres. Also to be discussed is a new collaborative effort to investigate the origin of WELs through non-LTE spectrum modeling. For this effort, new model atoms are being created for use in the codes TLUSTY and SYNSPEC.