Overview Document - Département d'Astrophysique, Géophysique ...

OVERVIEW DOCUMENT
1. INTRODUCTION - Title : Modern aspects of theoretical and observational (ground-based and
space-borne) astrophysics - Partners : Liège university (coordinator), K.U. Leuven, V.U. Brussel,
Royal Observatory (Brussels) - Budget : 2.5 Meuros - History : IAP started in phase IV (P4/05), continued during phase V
(P5/36), same title,
one additional partner in P5, i.e. V.U.B. - Document : this document deals with the main themes of the IAP, i.e.
asteroseismology, stellar and galactic evolution, massive stars and high
energy astrophysics, extragalactic astrophysics and the ILMT, high
angular resolution astrophysics.
2. RESEARCH RESULTS, etc Before presenting the reports on the main themes of the P5/36, I take
pleasure in stating that "DISTANT WORLDS", the 2005 Joint European and
National Astronomy Meeting (Liège, July 4-8, 2005), was an undoubtful
success. Based on the IAP themes, plus astrobiology and solar system
exploration, JENAM 2005 was definitely considered by its participants as an
excellent meeting, both through its outstanding plenary talks, and via its
topical workshops. Short reports on all these will appear in the fall of
2005 in the European Astronomical Society Newsletter. One of the ex-post evaluators was present at JENAM 2005, and he can
be asked about the above statements (as well as on the difficulties of
organizing such a meeting!) July 2005.
Jean-Pierre SWINGS
IAP coordinator I. Asteroseismology (all four partners) 1. Introduction
During the past few years, asteroseismologists of the Instituut voor
Sterrenkunde of the K.U.Leuven, of the Institut d'Astrophysique et de
Géophysique of the ULg, of the Royal Observatory of Belgium and of the
Observational Astronomy Group of the VUB have very successfully
collaborated on many different topics in asteroseismology (we refer to the
publication list in the annual reports of the previous IUAP). This implies
the participation of all the members of the Belgian Asteroseismology Group
(BAG). The BAG was founded in 2000 with the specific aim to coordinate all
the Belgian initiatives and expertises in asteroseismology, in order to
orient the relevant researches towards the upcoming data of pulsating stars
from space. It mostly concerns CoRoT, a French-led European mission, which
is in full preparation at present, with launch foreseen in 2006 and
lifetime of about two years. Several members of the BAG are involved in the
development of this mission. 2. Research results and 3. Networking (see also sections 4. and 5.2) We describe below some of our past, current and most important activities.
We limit ourselves to the results obtained through collaborations between
at least two AIP Institutes. Due to page limitation, we do not list
scientific results obtained by individual IAP Institutes, although they led
to numerous and important publications. A few important results from the
collaborations are given by the publication list and the various PhD
theses. The authors' lists as well as the PhD jury members reflect the
partnerships between the different IAP Institutes. 1) Hare and Hound exercises for the CoRoT mission H&H solar type star - In the context of the preparation of the CoRoT space
mission, "hare-hound" exercises were independently performed by several
teams of the CoRoT Seismology Working Group. The aim of such exercises,
which are commonly used in helioseismology, is to prepare the data analysis
and scientific interpretation of the asteroseismic CoRoT observations. This
will help in the development and testing of the tools which are needed for
the interpretation. The exercise was divided in four consecutive steps,
each performed independently by a different group:
1. Produce a set of theoretical oscillation frequencies (with
degrees = 0,1,2,3) and their rotational splittings for a stellar
model satisfying given constraints on luminosity L, effective
temperature Teff and chemical composition Z/X. A solar type star
was chosen.
2. Construct a CoRoT simulated time series including the set of
theoretical frequencies, CoRoT noise, stellar noise, inclination
angle of the rotation axis, amplitude and lifetime of the
modes...
3. Extract from the synthetic spectra the frequencies and
splittings with their formal errors leading to an "observed" set
of frequencies.
4. Derive the structure and rotation of the stellar model from the
set of frequencies.
For the CoRoT Week 3, which was organized in Liège in December 2002, we
joined the "hare and hound" exercice at step 4, from a different angle than
the other teams. We compared our numerical stellar evolution code and our
oscillation code to those used by other (French) teams. By comparing the
results of different "theoretical" codes, it is possible to get an estimate
of the "theoretical uncertainty" on the results. This is of course
essential for the interpretation of the future seismic data. We found that
for the solar-type star chosen for the exercise, we had an almost perfect
agreement with the results of the French Team, at least for the
evolutionary track of that star in the HR-diagram, and for the oscillations
of the star. We had to use slightly different parameters for the star. This
will need more in-depth analysis. H&H ( Cephei stars - We have performed two BAG CoRoT H&H exercises for B
stars, the results of which have been presented at the 4th CoRoT Week held
in June 2003 in Marseille. The conclusion of the CoRoT team was that a Beta
Cephei star should indeed be included in the primary targets of the CoRoT
mission. 2) ( Cephei stars 16 Lacertae - A seismic modelling of the massive star 16 Lac has been made.
We have compared a new spectroscopic mode identification with a photometric
identification based upon a non-adiabatic description of the eigenfunctions
in the star's atmosphere. Numerous theoretical models have been computed in
order to select the best model fitting the observed frequency values as
well as the mode identifications. The derived mass is 9.62 M( with an age
of 15.7 million years. ( Crucis - We have obtained photometric data assembled by the NASA space
mission WIRE of the [pic]Cephei star beta Crucis (Mimosa). A total of 5
million observations covering 17 days was analysed and the three main
periods found in this way are in perfect agreement with the results derived
earlier from line profile variations. The photometric amplitudes are small
(3, 2.7 and 0.6 millimag for the dominant modes), but this is not
surprising in view of the mode identifications derived earlier from the
line profiles. Additional periods of low-amplitude modes (between 0.2-0.3
mmag) are also derived, including one suggested earlier by the radial
velocity data. ( Centauri - We have performed an observational study of the orbital
motion and the intrinsic variability of the double-lined spectroscopic
binary ( Cen. Using 463 high signal-to-noise, high-resolution spectra
obtained over a timespan of 12 years it is shown that the radial velocity
of ( Cen varies with an orbital period of 357.0 days. We derive for the
first time the orbital parameters of the system and find a very eccentric
orbit (e=0.81) and similar component masses. ( Cen is a challenge for
current evolution scenarios in close binaries and it is also a puzzle: how
could a massive binary with such a large eccentricity have formed? The
primary exhibits line-profile variations. A period analysis performed on
the radial velocity variations of the primary after prewhitening the
orbital motion leads to the detection of at least 2 pulsation frequencies
while the star does not show any periodic photometric variability. ( Eri - We obtained results of a detailed seismic modelling of the (
Cephei star Eridani with the Liège evolution and pulsation codes. We
selected four clearly detected, well-identified and independent pulsation
modes from the frequency spectrum obtained from a recent five-month
multisite, multitechnique campaign, while previous modelling work only took
into account three frequencies. We show by means of a massive exploration
of the parameter space that no standard stellar model both matches and
excites these four observed modes, in contrast to the conclusion reached
when considering only three frequencies. Therefore, we have considered
stellar models with different metal mixtures and different initial hydrogen
abundance values. We show that an increase in the relative number fraction
of iron throughout the whole star or a large decrease in the initial
hydrogen abundance make the stellar models matching the four selected modes
satisfy all observational constraints and we provide the general properties
of the best of such physical models. Eclipsing binary HD 92024 - HD 92024 is an eclipsing binary with a (
Cephei primary. By combining the orbital and pulsational information from
this system, a strong seismic analysis is possible if the multiple modes of
oscillations can be identified. The bulk of observations have been
collected during the last 15 years, by collaborators from three IAP network
partners, at ESO, La Silla with in particular 4-band photometry from the
Strömgren Automatic Telescope (SAT). The most recent spectroscopic
observati