[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
[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.;
Zverko, J.; iňovský, 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
[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
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
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.;
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
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.; iňovský, 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