|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
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
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
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.
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.
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., iňovský, 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
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
the λ Bootis peculiarity is the accretion of interstellar
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.
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.
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
Krtička, J.; Mikulášek, Z.; Zverko, J.; iňovský, 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
simultaneously and consistently the magnetic field geometry and elemental
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,
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
and to recent theoretical investigations by Cunha (2006), which gives rise to
to trace magnetoacoustic effects in the atmosphere of this prototypical
Stratification analysis at phases of both magnetic extrema and our analysis of
magnetoacoustic pulsations enable us to unclose the vertical dimension in the
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.
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
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.; iňovský, 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.
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
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
There are no rotational modulation in the average spectra for the 6 different nights we analysed.
History of CP stars
Some introductory remarks about the historical development of the task of chemically peculiar
stars are given.
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
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.
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.
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.
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