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ANNUAL REPORT 2002
Interuniversity Attraction Pole
P5/36
~ ~ ~
Modern Aspects of Theoretical and Observational
(ground-based and space-borne) Astrophysics
Coordinator :
J.-P. SWINGS (Ulg)
Partners :
H. HENSBERGE (Royal Observatory, Brussels)
C. STERKEN (VUB)
C. WAELKENS (KU Leuven)
Preliminary considerations
The present report describes the scientific activities performed in 2002 in the frame of Inter
University Attraction Pole P 5/36, "Modern aspects of theoretical and observational (ground-based and
space-borne) astrophysics" : they are given in the five chapters dealing with the five work-packages of our
network. P 5/36, which is essentially a continuation of a network started in phase IV, includes now the
astronomy group of the Vrije Universiteit Brussel: the arrival of this group definitely strengthens some of
the work-packages of the IAP.
The personnel involved in the IAP research topics is given in the administrative report, i.e. the tables
requested by the OSTC : these tables are appended for information to the present report (Appendix 2).
A steering committee meeting was organized at OSTC1 on January 20, 2003 : on that occasion a
presentation of 2002 activities and highlights was delivered by the four partners and a discussion took place
on some recent developments. The OSTC representative recommended that our IAP network and activities
be put on the web : we are pleased to announce that the web pages and the links to the various research
teams and scientific topics (work packages) are essentially completed and will go "on line" very soon. Other
highlights or items that were presented to OSTC and that are worth recalling here were :
- the Belgian Asteroseismology Group (BAG) meetings and training courses;
- the third COROT week organized on December 4-7, 2002 in Liège (see details in the present
report);
- the international request by more than 40 institutes that the BAG (a real "spin-off" of the IAP) serve
as the catalyst for a European Network of Excellence in Asteroseismology as of 2003;
- the fact that some IAP partners (Liège in particular) saw their funding appreciably reduced
compared to the original proposal, which causes problems in achieving all the intended scientific
goals;
- the encouraging news that the involvement of several young researchers in themes related to
interferometry has progressed well in 2002.
Seven IAP-related doctoral dissertations were defended in 2002 : their list is given in Appendix 1. It
is to be noted that three of them involved collaborations between ULg and KU Leuven.
Jean-Pierre Swings
Coordinator
March 2003
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Participants : C. Lejour (OSTC), H. Hensberge (ROB), C. Sterken (VUB), C. Waelkens (KU Leuven), A. Noels &
J.P. Swings (Ulg).
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I. Asteroseismology
During the past few years, asteroseismologists of the Instituut voor Sterrenkunde of the K.U.Leuven, of the
Institut d'Astrophysique et Géophysique of the ULg and of the Royal Observatory of Belgium have
succesfully collaborated on many different topics in asteroseismology (we refer to the publication list in the
annual reports of the previous IUAP). The collaboration is now extended to the Observational Astronomy
Group of the V.U.B. 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 research 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 2005 and lifetime of about two years, as well as the
preparation of the ESA Eddington mission, planned for launch in 2008. Several members of the BAG are
involved in the development of these two missions.
A  Cephei star : 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 atmosphere. Numerous theoretical models have been computed in order to select
the model best 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.
Another  Cephei star :  Crucis
We have obtained photometric data assembled by the NASA space mission WIRE of the  Cephei star beta
Crucis (Mimosa). A total of 5 million observations covering 17 days were 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.
Yet another  Cephei star :  Centauri
We have performed an observational study of the orbital motion and the intrinsic variability of the doublelined 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 with a mass ratio M1/M2=1.02.  Cen forms a challenge for current evolution
scenarios in close binaries and it is also a puzzle how a massive binary with such a large eccentricity could
have formed in the first place. Both the primary and the secondary exhibit 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 3 pulsation frequencies while the star does not show any periodic
photometric variability.
Eclipsing binary HD 92024
Spectra of the eclipsing binary HD 92024, which has a  Cephei primary, were obtained with FEROS (ESO,
La Silla). Together with the spectra obtained one year earlier, the data set contains now about 100 spectra,
which cover well the orbital period. The orbital radial velocities are currently determined using a new
method which uses exclusively differential radial velocity measurements from spectra showing very similar
line profiles i.e.eliminating largely the contributions of the pulsations to the line shifts. Photometry is
collected since December and will be obtained further during the first half of 2003 in cooperation with the
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Univ.of Copenhagen and VUB at the SAT telescope at La Silla. The effort concentrates on the phases of the
secondary eclipse, to disentangle the depth and the shape of that eclipse from the light variations due to
stellar pulsation. The photometry is being pre-whitened for pulsation variations, using also a large database
available at VUB. In 2003, an accurate orbit for the eclipsing system will be derived from the light curve and
the radial velocity data. After removal of the orbital effects, the pulsation effects in the line profiles will be
studied. In the framework of this study, improvements to the reduction of echelle spectra were further
developed, most importantly regarding the merging of the spectral orders. Meanwhile, these improvements
are (partly) exported to the ULg group studying Luminous Massive Stars and to Copenhagen University.
Similar improvements have been introduced in the pipeline for the HEROS echelle spectrograph at Ondrejov
Astronomical Observatory, Czechia.
A slowly pulsating B star : HD 147394
In the framework of a long-term spectroscopic and photometric monitoring of slowly pulsating B stars we
studied thoroughly the northern target star HD 147394. We performed an end-to-end analysis, consisting of
a frequency analysis, a mode identification from line-profile variations and a comparison with theoretical
pulsation models.
A  Scuti star : XX Pyx
Spectroscopic and multicolour photometric evidence was presented, supporting the binary nature of the 
Scuti star XX Pyx. Applying a cross-correlation technique to the spectra, we found clear radial-velocity
variations with a large amplitude. We derive the orbital parameters and confirm an orbital period of 1.15d,
as suggested previously on the basis of photometric variations. The amplitude of the slow variations present
in our new multicolour data is wavelength independent, pointing also to a geometric effect as origin of the
variability. They are thus fully consistent with the spectral variations and are interpreted as ellipsoidal
variations. XX Pyx has a circular orbit of which the radial-velocity variations have a semi-amplitude of
17.8+/-0.4km s-1. The single-lined binary nature of the star, together with the mass function, lead us to
conclude that the orbital inclination must be larger than 10 degrees. The orbital solution is compatible with a
synchronized M3V companion. The deformation of the primary due to tidal forces is very probably the
reason for the failure of detailed seismic modelling efforts done recently.
A solar-type star :  Cen
Models of  Cen A & B have been computed using a new mass determination together with seismological
data obtained very recently. These new data do help improve our knowledge of the evolutionary status of the
system. All the constraints are satisfied with a model which gives an age of about 6 Gyr for the binary.
 Doradus stars
We have reported on our results from a large photometric campaign on thirty five  Dor star candidates
undertaken in the framework of the Flanders -South-Africa project. An overview of the data, as well as the
results of the analysis of the obtained time series are presented, the main conclusion being that nine stars are
thought to be multiperiodic gamma Dor stars and eight monoperiodic. We also performed a photometric
mode identification for two stars of the sample by comparing the amplitude ratios in the different passbands
of the Geneva photometric system. Both stars seem to pulsate in non-radial modes of degree l = 1.
Variable stars in the open cluster NGC1817
Time-series and narrow-band photometry of the young, open cluster NGC1817 were collected during five
nights at the 2.56m Nordic Optical Telescope, La Palma/Spain. These data will provide confirmed periods of
known  Sct variables and estimates of stellar parameters such as temperature for the cluster members inside
two sub-fields of the cluster. This is a collaboration between VUB, ROB and Univ. Aarhus, Denmark.
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Variable stars in the globular cluster  Centauri
In a cooperation between VUB, ROB and collaborators in Germany, Denmark and Italy on monitoring of
variable stars in the globular cluster  Centauri, the first high-quality colour-magnitude diagrams were
obtained from the observations. These data from ESO VLT are of excellent quality showing a very precise
turnoff-point from the main sequence for the cluster's youngest stellar population. Application of these data
in preliminary reductions of time-series data from the Danish 1.54m telescope at La Silla revealed three new
SX Phe candidates with very short periods.
Non-adiabatic analysis of pulsating stars
The study of the non-adiabatic character of stellar oscillations can give precise information about their
internal structure. First, we studied in detail the influence of non-adiabatic temperature variations on line
profile variations of B-type pulsators. Our non-adiabatic pulsation code also allows to determine the
theoretical amplitude ratios and phase differences of the light curve as seen in different colour filters. By
confronting these theoretical predictions to the observations, it is possible on one hand to determine the
degree l of the modes and, on the other hand, to obtain precise information about the stars. We call this
method Non-adiabatic Asteroseismology. We applied this method to the study of B-type pulsators and
showed that strong constraints on the metallicity of these stars can be obtained by this approach. We applied
also this method to the study of A- and F-type pulsators, in a close collaboration with the Instituto de
Astrofisica de Andalucia, Spain. We showed that the characteristics of the thin convective envelope of these
stars can be constrained with this approach. Our last works in this frame have been to include the new
ATLAS9 atmosphere models in our non-adiabatic code. These models have been computed using three
different convection treatments (mixing length theory -MLT-, Canuto and Mazzitelli (1991), and Canuto,
Goldmann and Mazziteli 1996) and therefore allow us to compute complete (atmosphere and interior) stellar
models with a consistent treatment of convection.
Spectroscopic analysis of pulsating stars
We implemented a new version of the moment method to identify modes of pulsating stars from highresolution spectroscopy. This new version is generalised to rotating stars and is more appropriate to
multiperiodic stars than any of the other methods available thus far. We have applied the new method to
several pulsating B stars and will continue to do so in the near future.
Hare and Hound exercises for the COROT mission
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 life time of the modes.....
3) Extract from the synthetic spectra the frequencies and splittings with their formal errors leading to an
"observed'' set of frequencies.
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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, 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.
We are currently running two BAG COROT H&H exercises for B stars, the results of which will be
presented at the 4th COROT week in France mid-2003.
Organization of the Third COROT Week
The Third COROT Week was held in Liège, December 4 to 7, 2002. See the Web site :
http://www.astro.ulg.ac.be/orientation/asterosis/week3/week3.html
Publications in 2002
1. Common to more than one institute :
Aerts, C., Lehmann, H., Briquet, M., Scuflaire, R., Dupret, M. A., De Ridder, J., Thoul, A., 2003,
Spectroscopic mode identification for the  Cephei star EN (16) Lacertae, A&A 399, 639-645
Briquet, M., Aerts, C., 2003, A new version of the moment method, optimized for mode identification in
multiperiodic stars, A&A 398, 687-696
Aerts, C., Handler, G. Arentoft, T., Vandenbussche, B., Medupe, R., Sterken, C., 2002, The  Scuti stars XX
Pyx is an ellipsoidal variable, MNRAS 333, L35-L39
Cuypers, J., Aerts, C., Buzasi, D., Catanzarite, J., Conrow, T., Laher, R., 2002, Multiperiodicity in the light
variations of the  Cephei star  Crucis, A&A 392, 599-603
Ausseloos, M., Aerts, C., Uytterhoeven, K., Schrijvers, C., Waelkens, C., Cuypers, J., 2002,  Centauri: An
eccentric binary with two -Cep-type components, A&A 384, 209-214
M.-A. Dupret, J. De Ridder, C. Neuforge, C. Aerts, R. Scuflaire, 2002. Influence of non-adiabatic
temperature variations on line profile variations of slowly rotating Cep stars and SPBs. I. Non-adiabatic
eigenfunctions in the atmosphere of a pulsating star. A&A, 385, 563-571.
J. De Ridder, M.-A. Dupret, C. Neuforge, C. Aerts, 2002. Influence of nonadiabatic temperature variations
on line profile variations of slowly-rotating  Cephei stars and SPBs. II. Simulations of line profile time
series. A&A, 385, 572-584.
J. De Ridder, C. Aerts, M.-A. Dupret, C. Neuforge, 2002. Do temperature variations at the surface of a hot
non-radial pulsator change significantly the line-profile variations ? In Radial and nonradial pulsations as
probes of stellar physics, IAU Coll. 185, eds C. Aerts, T.R. Bedding, J. Christensen-Dalsgaard, ASP
Conference Series, vol. 259, 218-221.
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P. Mathias, J.-M. Le Contel, C. Aerts, P. De Cat, H. Van Winckel, E. Robbrecht, M. Briquet, J. Cuypers,
2002. Spectroscopic monitoring of 10 northern SPB candidates. In Radial and nonradial pulsations as
probes of stellar physics, IAU Coll. 185, eds C. Aerts, T.R. Bedding, J. Christensen-Dalsgaard, ASP
Conference Series, vol. 259, 232-233.
M. Briquet, A. Noels, C. Aerts, P. Mathias, 2002. The slowly pulsating B star HD 147394. In Radial and
nonradial pulsations as probes of stellar physics, IAU Coll. 185, eds C. Aerts, T.R. Bedding, J. ChristensenDalsgaard, ASP Conference Series, vol. 259, 234-235.
M. Briquet, R. Scuflaire, C. Aerts, P. De Cat, 2002. Detailed line-profile modeling of B stars with chemical
inhomogeneities. In Radial and nonradial pulsations as probes of stellar physics, IAU Coll. 185, eds C.
Aerts, T.R. Bedding, J. Christensen-Dalsgaard, ASP Conference Series, vol. 259, 266-269.
M.-A. Dupret, R. Garrido, J. De Ridder, R. Scuflaire, P. De Cat, C. Aerts, A. Moya, A. Noels, A. Thoul,
2002. An improved photometric mode identification method\string: applications to Slowly Pulsating B
stars,  Cephei,  Scuti and  Doradus stars (communication). Asteroseismology across the HR Diagram,
Porto, 1-5 July 2002.
C. Aerts, H. Lehmann, M.-A. Dupret, M. Briquet, J. De Ridder, R. Scuflaire, A. Thoul, 2002. Mode
Identification and Seismic Modelling in the Cep Star EN (16) Lac (poster). Asteroseismology across the HR
Diagram, Porto, 1-5 July 2002.
C. Aerts, J. Cuypers, M.-A. Dupret, R. Garrido, J. De Ridder, L. Eyer, 2002. Photometric mode
identification in the two  Doradus stars HD 12901 and HD 48501 (poster). Asteroseismology across the HR
Diagram, Porto, 1-5 July 2002.
M. Briquet, C. Aerts, 2002. A new version of the moment method, optimized for mode identification in
multiperiodic stars (poster). Asteroseismology across the HR Diagram, Porto, 1-5 July 2002.
R. Garrido, M.-A. Dupret, A. Claret, A. Moya, 2002. Non-adiabatic pulsational observables of Gamma Dor
and Delta Scuti stars: comparison of two different numerical codes (poster). Asteroseismology across the
HR Diagram, Porto, 1-5 July 2002.
M.-A. Dupret, R. Scuflaire, R. Garrido, J. De Ridder, C. Aerts, P. De Cat, A. Moya, J. Montalban, A. Noels,
A. Thoul. Non-adiabatic asteroseismology and the COROT space mission (poster). COROT Week 3, Liège,
4-7 December 2002.
http://www.astro.ulg.ac.be/orientation/asterosis/week3/texte/papers.html
Freyhammer L.M., Andersen M.I., Arentoft T., Sterken C., Nørregaard P.: 2002, Experimental Astronomy,
12 no.3 (2001), 147 On cross-talk correction of images from multiple-port CCDs
Sterken, C., Knudsen, M.R., Duerbeck, H.W., Arentoft, T., Freyhammer, L.M., et al., 2002, in
"Observational Aspects of pulsating B and A stars" (eds. C. Sterken and D. W. Kurtz), ASP Conf. Series
256, 183 A search for new variable stars in NGC 6231
Eyer, L., Aerts, C., Van Loon, M., Boukaert, P. Cuypers, J., 2002, in "Observational Aspects of pulsating B
and A stars" (eds. C. Sterken and D. W. Kurtz), ASP Conf. Series 256, 203, The FlanSA  Doradus Stars
Campaign
Freyhammer, L.M., Clausen, J.V., Arentoft, T., Sterken, C., 2002, in: Observational aspects of pulsating Band A stars (eds. C. Sterken, D.W. Kurtz), ASP Conf. Series 256,157 Multi-colour photometry of eclipsing
binaries in open clusters: CPD-592628
Cuypers, J., Aerts, C., Buzasi, D., Catanzarite, J., Conrow, T., Laher, R., 2002, in: 1st Eddington Workshop,
ed. F. Favata, ESA-SP 485, 41-47, Asteroseismology "on a WIRE''
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2. From one institute :
a. Liège :
A. Thoul, R. Scuflaire, B. Vatovez, A. Noels, P. Magain. Ground-based asteroseismology of Cen: An
urgent need for space observations (poster). 2nd Corot Week, Paris, 13-16 may 2002.
A. Thoul, R. Scuflaire, A. Noels, B. Vatovez, P. Magain. Asteroseismology of Alpha Centauri
(communication). Groupe de Contact FNRS Astronomie et Astrophysique, Bruxelles, 31 May 2002.
A. Thoul, R. Scuflaire, B. Vatovez, A. Noels, 2002. p-mode oscillations of  Cen A: the need for space
asterosismology (communication). Asteroseismology across the HR Diagram, Porto, 1-5 July 2002.
R. Scuflaire, 2002. Non-adiabatic analysis\string: activity and progress report (communication). COROT
Week 3, Liège, 4-7 December 2002.
http://www.astro.ulg.ac.be/orientation/asterosis/week3/texte/papers.html
A. Thoul, R. Scuflaire, A. Noels, M. Briquet, M.-A. Dupret. The star of H&H2: comparing stellar evolution
codes (poster). COROT Week 3, Liège, 4-7 December 2002.
J. Montalban, M.-A. Dupret, I. Mazitelli, F. Kupka, 2002. Effect of convection treatment on non-adiabatic
eigenfuctions (poster). COROT Week 3, Liège, 4-7 December 2002.
http://www.astro.ulg.ac.be/orientation/asterosis/week3/texte/papers.html
b. ROB :
Arentoft, T., Freyhammer, L.M., 2002, in: Extragalactic Star Clusters (eds. E.K. Grebel, D. Geisler, D.
Minniti), IAU Symposium 207, 135. Cluster distances using  Scuti stars - The open clusters Praesepe and
NGC 7062
Freyhammer, L.M., Petersen, J.O., 2002, in: Extragalactic Star Clusters (eds. E.K. Grebel, D. Geisler, D.
Minniti), IAU Symposium 207, 138 Cluster distances using  Scuti stars - Oscillating blue stragglers in 
Centauri
Ilijic, S., Hensberge, H., Pavlovski, K., 2002, Fizika B 10, 357 Separation Techniques for Disentangling of
Composite Spectra
Symposia, Colloquia, Workshops: (financed by IAP)
Courses, Belgian Asteroseismolgy Group, Leuven, 11-12 Apr (H. Hensberge, L.M. Freyhammer),
Liège 5-6 Sep (L.M. Freyhammer)
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II. STELLAR & GALACTIC EVOLUTION
From the ULg Group
From the spectral analysis of a sample of old stars based on data of unprecedented quality, the team of Liège
discovered peculiar abundance correlations, which have led it to propose a new scenario for the origin of
both the halo field stars and the halo globular clusters (GC). This so-called EASE scenario (for
Evaporation/Accretion/Self Enrichment) proposes that most halo field stars were born in proto-globular
clusters and that, contrary to what was generally assumed, these GCs have undergone a chemical evolution.
During a first phase, massive stars explode as Type II Supernovae, chemically enrich the surrounding cloud
gas and sweep it into an expanding supershell. A second stellar generation may form out of the chemically
enriched shell and may then recollapse to form a GC. In a second phase, the atmospheres of the GC stars
were polluted by accretion of matter expelled from intermediate mass Asymptotic Giant Branch (AGB)
stars. These polluted stars should display overabundances in the elements synthesized by the AGB stars (in
particular, carbon and heavy elements). The few data available on unevolved GC star, show indeed
abundance anomalies which seem to confirm that accretion may have played a role.
Regarding the first phase, supernova energetics, namely the (presumed) ability of supernovae to completely
disrupt the cloud of gas out of which they have formed, has been a major criticism to the GC self-enrichment
hypothesis. In order to revise this point, we develop a model of GC self-enrichment based on the ability of
their gaseous progenitors to retain the ejecta of a first generation of Type II Supernovae. We show that,
contrary to what was generally believed, a proto-globular cloud can sustain the sequence of several tens of
supernovae required to build up metallicities typical of the Galactic halo. This model predicts some
properties of the present-day globular cluster system (e.g. a metallicity gradient and a mass-metallicity
anticorrelation) which have been successfully confronted to the data related to the Old Halo subsystem of
GCs. Along with the chemical enrichment of the initially primordial parent cloud, the supernovae may also
trigger the formation of a second generation of stars which may, provided they get bound, form a GC at a
later time. We show that (some of) the swept clouds indeed encounter physical conditions favouring their
transverse collapse and seeding thereby the formation of new stars. Moreover, our results point clearly to a
relation between the achieved metallicity and the probability of star formation, opening thereby the way to
the understanding of the metallicity distribution functions of both halo field stars and halo GCs.
The second phase of the EASE scenario, the accretion phase, can now be tested in much more detail thanks
to the availability of high resolution spectrographs on the VLT: the chemical composition of the individual
halo field stars can be studied as a function of their kinematic properties and compared to the results for
GCs; accurate abundances can be obtained for unevolved stars in a few GCs, allowing to test in situ the
enrichment scenario; the surface abundances of stars with very different convective envelopes and, thus,
very different degrees of dilution of the accreted material, would allow a detailed study of the accretion
scenario.
Until relatively recently, a significant fraction of the astrophysical community would have probably argued
that GC formation was restricted to the early evolution of the Universe. This idea has deeply evolved due to
the detection of systems of young massive stellar clusters in merging or interacting galaxies. In the frame of
a collaboration with the Institute of Astronomy of the Cambridge University (UK), the study of an
intermediate age starburst site of the irregular galaxy M82 has been performed. Based on accurate HST
photometry, the age, the metallicity and the mass of about one hundred massive stellar clusters have been
estimated. Interestingly, the clusters located in the eastern part of the starburst site shows a mass-metallicity
anticorrelation in the sense expected by the self-enrichment scenario. Obviously, reliable data about
extragalactic systems of massive stellar clusters are highly desirable to perform some more tests of the selfenrichment model. In the meantime, this type of studies raises the question of the accuracy of the derived
cluster age, metallicity and mass from integrated photometry. We have now therefore embarked on a project
to study the systematic uncertainties inherent to the most popular methods.
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Refereed Publications (since 2002)
Thoul A.A., Jorissen A., Goriely S., Jehin E., Magain P., Noels A., Parmentier G. (2002) Accretion of gas
by globular cluster stars. A&A 383, 491-501
Parmentier G., de Grijs R., Gilmore G. (2003) Chemical evolution of the M82~B fossil starburst. MNRAS,
accepted for publication
Conference Proceedings
"Self-Enrichment and Formation of Galactic Halo GlobularClusters". G. Parmentier, A. Noels, G. Gilmore,
in Proceedings of "New Horizonsin Globular Cluster Astronomy'', G.~Piotto, G.~Meylan, G.~Djorgovski,
M. Riello (eds.), ASP conference series, in press
"The M82~B Fossil Starburst". G. Parmentier, R. de Grijs, G. Gilmore, in Proceedings of "New Horizons in
Globular Cluster Astronomy'', G.~Piotto, G. Meylan, G.~Djorgovski, M. Riello (eds.), ASP conference
series, in press
"Accretion of gas by globular cluster stars''. Thoul A.A., Jorissen A., Goriely S., Jehin E., Magain P., Noels
A., Parmentier G., in Proceedings of New Horizons in Globular Cluster Astronomy'', G. Piotto, G. Meylan,
G. Djorgovski, M. Riello (eds.), ASP conference series, in press
"Blue Stragglers and the EASE scenario''. Noels A., Scuflaire R., Magain P., Parmentier G., Thoul A.A., in
Proceedings of "Asteroseismology across the HR Diagram'', in press
"Formation History of Star Clusters in M82 B''. G. Parmentier, R. de Grijs, G. Gilmore, in Proceedings of
"Extragalactic Globular Cluster Systems'', M.~Kissler-Patig (ed), Springer-Verlag series "ESO Astrophysics
Symposia", in press
From the Royal Observatory Brussels
Project: Post-AGB stars and surrounding shells
T. Ueta has completed a paper describing the 2-dimensional, axisymmetric dust radiative-transfer code he
developed in collaboration with M. Meixner (STScI) at the University of Illinois at Urbana-Champaign
before he started his appointment at ROB. The paper has been accepted for publication in ApJ (April 2003
issue). T. Ueta has also compiled a final data set of the near-infrared photometry for nearly 80 post-AGB
objects. This photometric survey was done with NIRIM mounted on the 1 m telescope at the Mt. Laguna
Observatory (Southern California, USA) between 1997 and 2000. The project had been carried out in
collaboration with M. Meixner (STScI) and undergraduate students at the University of Illinois at UrbanaChampaign. The paper has been accepted for publication in the AJ (April 2003 issue).
T. Ueta has analysed the radio interferometric data of post-AGB stars obtained using the BIMA Radio
Interferometric Array in Northern California in collaboration with M. Meixner (STScI) and D. Fong (Univ.
of Illinois), in order to study the distribution and kinematics of CO gas surrounding these evolved stars. The
data analysis is currently on-going.
As a Japanese citizen Toshiya Ueta has some access to the 8-m Subaru telescope in Hawaii. He and G. Van
de Steene submitted joint proposals to the Subaru telescope to study the shock physics in AFGL 618 and
AFGL 2688. We are interested to study the formation of PNe and to this end we submitted an observing
proposal to detect the signs of asphericity in AGB and post-AGB shells. In the coming year we intend to
investigate the possibilities of the VLTI to study the dust shells in order to gain understanding in the
formation of planetary nebulae.
10
G. Van de Steene in collaboration with P. van Hoof investigated the shocked H2 emission in the post-AGB
star 16594-4656. The article is submitted to A&A.
In collaboration with P. van Hoof (Queens University Belfast), Ueta and Van de Steene want to determine
the spectral types and stellar temperatures of a statistically significant sample of post-AGB stars across the
Hertzsprung-Russell diagram. Such a sample is invaluable for testing the mass-loss recipes used in stellar
evolution models. This will lead to more realistic post-AGB evolution models and a better understanding of
the role of post-AGB winds in planetary nebula formation.
The VLT-UVES data have been analyzed. In collaboration with Drs. D. Jevremovic from Queens University
Belfast, we are calculating unified NLTE-models with the most current version of the PHOENIX code to
determine simultaneously the wind velocity and chemical abundances of the objects. The model parameters
need to be refined further and the recently added wind module in the code needs additional validation. More
echelle spectra will be obtained to study the variability in the line profiles.
In order to foster cooperation between the IAP partners on the subject of post-AGB stars, T. Ueta has given,
shortly after his recent appointment, seminars at the ROB and the KULeuven on the subject in general and
the analysis codes he developed in particular.
Project: Numerical study of the chemo-dynamical evolution of galaxies
The formation and evolution of galaxies is certainly one of the most important research topics in
astrophysics. Even with the many advances registered in the last 10 years or so, both observationally and
theoretically, we are still far from a satisfactory theory. The problem lies in the complexity of the subject: a
galaxy evolves under the action of gravity, through the transformation of its gas into stars (a process still
poorly known) and through the interaction of this gas with the energy liberated by dying stars. These three
aspects of galactic evolution (chemistry, photometry and dynamics) are in general studied separately.
There is up to now, no "unified" treatment of all the galactic properties, which would allow to confront
theoretical predictions with the many observational data available (and to come, especially with the 10m
class telescopes). We have therefore started a collaboration to undertake this unified study on the theoretical
side. The idea is to develop a numerical code to treat in a very detailed way the dynamical, photometric and
chemical aspects of the evolution of galaxies. The study of the dynamical aspects will be done through a
three-dimensional hydrodynamic code.
We have started this program in November 2002 at the Royal Observatory (Henri Boffin, Yves Busegnies)
in collaboration with the Institut d'Astronomie et d'Astrophysique de l'Université Libre de Bruxelles (Prof.
Marcel Arnould, Abdel Messoudi) and the Institut d'Astrophysique de Paris (Nikos Prantzos). As a first step,
we have adapted a TreeSPH hydrodynamic code in order to be able to deal with the study of the formation
and evolution of galaxy. We have now completed this stage and are now including, in a step-by-step
process, more and more physical ingredients. First, we will introduce cooling and heating, then the star
formation and the feedback from Supernovae to the interstellar gas.
Publications
In press :
Ueta, T., Meixner, M., Moser, D. E., Pyzowski, L. A., & Davis, J. S., 2003, AJ (in press)
Near-Infrared Photometric Survey of Proto-Planetary Nebula Candidates
Ueta, T., & Meixner, M., 2003, ApJ (in press)
2-Dust: a Radiative Transfer Code for an Axisymmetric System
Van de Steene, G.C., van Hoof, P.A.M., 2003, A&A (in press)
Shock emission in the post-AGB star IRAS 16594-4656
11
III. Massive Luminous Stars & High Energy Astrophysics
In 2002, we have continued our multi-wavelength analyses of massive stars. An important effort was
devoted to the study of O-stars that are known to display non-thermal radio emission. This phenomenon is
attributed to synchrotron emission by relativistic electrons accelerated in strong hydrodynamic shocks in the
stellar wind. One open question related to these objects is whether the shocks arise in the wind of a single Ostar or in the wind interaction zone of a binary system. In this context, we have studied the O4V star 9Sgr.
Taking advantage of the expertises of the partners of the IUAP network, we were able to combine X-ray data
from XMM-Newton, radio data obtained with the VLA as well as optical spectroscopy (Rauw et al. 2002b,
joint publication between the Liège and ROB teams). We find that the hard X-ray emission of 9Sgr could
either be attributed to a population of relativistic electrons accelerated in shocks with surprisingly low
compression ratios of  1.8 or to a thermal plasma at a temperature  20 million K. The simultaneous VLA
data clearly indicate a non-thermal radio emission that could also be explained by electrons accelerated in
shocks with rather low compression ratios. Our optical spectra further reveal long-term radial velocity
variations suggesting that the relativistic electrons could be accelerated in a colliding wind phenomenon
arising in a binary system. We are presently analysing coordinated X-ray and radio observations of two other
non-thermal radio emitters (HD168112 and HD167971). Further analysis of observations of a number of
non-thermal radio emitters in the VLA archive is also in progress.
In the framework of our research on the non-thermal emission from possibly single O stars, we developed
and tested a numerical code that simulates their synchrotron radio emission. This code was subsequently
applied to 9 Sgr (Rauw et al. 2002b). For the O5 If star Cyg OB2
No 9 we performed a detailed analysis of simultaneous observations at 2, 6 and 20 cm. It was found that,
regardless of most other parameters, the outer boundary of the synchrotron emission region is welldetermined.
In the framework of the international XMEGA collaboration, one of our PhD students (Y. Nazé) led the
team that analysed the X-ray and optical data of the young open cluster NGC 346 in the SMC. The Chandra
X-ray data provided the first detection of the enigmatic WR binary HD 5980 and of the NGC 346 cluster
(Nazé et al. 2002a and 2003). HD 5980 is an exceptional binary system that underwent an LBV-like eruption
in 1994. Its variable X-ray luminosity is rather high and could only be explained by means of colliding
winds or post-eruption effects. These observations also led to the discovery of 75 X-ray serendipitous
sources. Thanks to our WFI optical data, we have identified most of them as X-ray binaries. An ongoing
comparison with a subsequent XMM observation seems to reinforce this hypothesis.
We have also continued our investigation of massive binary systems with the aim of determining the
fundamental parameters of their components and the properties of the interaction between their stellar winds
(Albacete Colombo et al. 2002; Sana et al. 2002, 2003; Rauw et al. 2002a,d). For instance, we have studied
the evolved massive binary HDE228766 (Rauw et al. 2002d). Using a tomographic technique to investigate
the profile variability of the broad emission lines, we find evidence for an extra H emission that is probably
associated with a wind interaction region located near the surface of the primary star. Our analysis of the
spectrum with a non-LTE code indicates that the secondary is an evolved object that exhibits CNO
processed material in its atmosphere and has a large mass loss rate.
Combining the expertises of the various IUAP network partners, we were able to establish the first reliable
SB2 orbital solution of the eclipsing O-star binary CPD-41° 7742 based on an extensive set of spectra
obtained with the FEROS spectrograph at ESO (Sana et al. 2003, joint publication between the Liège and
ROB teams). The results from this study will help to improve our knowledge of the still poorly constrained
mass – luminosity relation of early-type main sequence stars.
We have also reported the first results of our XMM-Newton observing campaign of colliding wind earlytype binaries. Phase-resolved EPIC spectroscopy of the eccentric binary HD93403 reveals a clear orbital
modulation of the X-ray luminosity that results from a combination of the changing wind opacity along the
binary orbit and the variation of the colliding wind X-ray emission as a function of orbital separation (Rauw
et al. 2002a). Optical monitoring of this system further indicates a strong variability of the HeII 4686 and
H line profiles suggesting that part of the emission arises in the trailing arm of a shock cone wrapped
12
around the secondary.
Another well-known massive binary has also been the subject of one of our observational campaigns with
XMM-Newton. Phase resolved X-ray observations covering half the orbit of the WR + O binary WR22 have
been acquired. Preliminary results have been presented at the IAU Symposium nr.212 (June 2002, see
Gosset et al. in press). The X-ray spectrum of WR22 is characterized by a hard tail that remains stable along
the orbit whereas the observed flux on the soft side of the spectrum markedly decreases when the star goes
from apoastron to periastron. This system offers an additional configuration and a unique opportunity to
scan the extended atmosphere of a Wolf-Rayet star. A paper is expected to be completed soon.
In the framework of this project, one of our PhD students (H. Sana) spent several months at the University of
Birmingham (UK) to perform hydrodynamical simulations of wind collisions in massive binaries. These
simulations are currently being compared to the XMM observations of HD152248 and the results will be
published in 2003.
We have also continued our analyses of the spectroscopic variability of luminous O stars. Our observations
of the Oef stars BD+60°2522 (Rauw et al. 2003), HD192281 and HD14442 (De Becker & Rauw 2003)
reveal modulations of the double-peaked He II 4686 emission line on time scales that could be related to the
stellar rotational period. However, in the case of BD+60° 2522, the time scale as well as the pattern of these
variations turn out to be epoch dependent and the phenomenon is thus most likely not ruled by a single
stable clock. This situation could arise through the beating of several non-radial pulsation modes that trigger
transient large-scale density perturbations in a confined stellar wind.
We have continued our investigation of the thermal radio and millimetre continuum of massive stars. In
particular, our observations of ζ Pup and ε Ori with the VLA, ATCA and JCMT (wavelengths ranging from
800 microns to 20 cm) were analysed together with observations from the VLA archive. There is no
indication of variability at any of these wavelengths. For both stars there is, however, unambiguous excess
millimetre emission with respect to the emission expected from the radio continuum. This may point to the
presence of structures in the millimetre formation region (>10 R*). Other possible explanations are currently
being considered.
One goal of this study is to use these observations to distinguish between coherent, large-scale structure and
stochastic, small-scale structure. To this aim, we have developed a three-dimensional radiative transfer code
to predict in which wavelength domain coherent structure may cause detectable continuum variability.
With regard to the presence of structures in the millimetre and radio formation region, we have pursued our
time-dependent hydrodynamical modelling of the winds of massive stars. A new technique, allowing more
accurate models at lower computational cost, has been developed (Runacres 2003, RevMxAA 15, 217).
An important effort was devoted to the investigation of the circumstellar environment of massive stars. Due
to their strong energetic winds, O and WR stars are able to sweep the ambient medium into a thin shell,
thereby creating a 'bubble'. We performed a study of 3 candidate bubbles in the N44 nebula in the LMC.
Using high dispersion spectroscopy and high resolution images from the HST, we discovered that although
the overall properties of these bubbles do not contradict strongly the theoretical expectations, the presence of
exceptional dust pillars undermines this apparent agreement (Nazé et al. 2002b). Using new VLT
observations, we also started the first detailed study of the morphology and energetics of a set of peculiar,
highly excited nebulae associated with massive stars in the LMC. This work is currently being completed.
As a by-product of our X-ray observations of massive stars, we have started an investigation of the star
formation processes in OB associations and very young open clusters. For instance, our XMM-Newton
observation of the Lagoon Nebula (M8) reveals a cluster of point sources, most of which have optical
counterparts inside the very young open cluster NGC6530 (Rauw et al. 2002c, joint publication between the
Liège and ROB teams). The bulk of these X-ray sources are associated with low and intermediate mass premain sequence stars and suggest a close connection between the massive stars and the newly formed lowmass PMS objects.
We further carried on our program of search for Wolf-Rayet stars in galaxies of the Local Group and slightly
beyond.This is an ongoing collaboration between the Liège group and Dr. P. Royer from KU Leuven. The
evolution of massive stars is dependent on several factors among which the mass-loss rate is certainly one of
13
the most important. It is commonly believed that the mass-loss is dependent on the metallicity. Therefore,
the study of the populations of O and Wolf-Rayet stars in places and galaxies of different ambient
metallicities is expected to bring direct constraints on the evolutionary models. The recognition and
classification of these massive stars in a homogeneous and coherent survey is a prerequisite to a study of the
evolution of these massive stars. On the mere basis of particular very narrow band photometry (system
designed in Liège), we are able to recognize and classify Wolf-Rayet stars even in crowded regions. In 2002,
we obtained 3 nights on the ESO VLT to apply the method. Following eye inspection and preliminary
reduction of the images, we identified several Wolf-Rayet stars in NGC300 and discovered the first ten WRs
in the galaxy NGC1313. The reduction is in progress.
Finally, the GAPHE team is also involved in the tracing of large scale structures on the basis of an XMMNewton search for galaxy clusters and AGNs (see the AEOS part).
Publications
1. Common to more than one institute
Refereed Journals :
A multi-wavelength investigation of the non-thermal radio emitting O-star 9Sgr
Rauw, G.; Blomme, R.; Waldron, W.L.; Corcoran, M.F.; Pittard, J.M.; Pollock, A.M.T.; Runacres, M.C.;
Sana, H.; Stevens, I.R.; & Van Loo, S. 2002, A&A 394, 993
An XMM-Newton observation of the Lagoon Nebula and the very young open cluster NGC6530
Rauw, G.; Nazé, Y.; Gosset, E.; Stevens, I.R.; Blomme, R.; Corcoran, M.F.; Pittard, J.M.; & Runacres,
M.C. 2002, A&A 395, 499
Spectroscopic and photometric observations of the recurrent nova IM Normae
Duerbeck, H. W., Sterken, C., Baptista, R., Diaz, M.P., Dutra, C.M., Freyhammer, L., Hensberge, H., Jones,
A.F., 2002, in : Classical Nova Explosions (eds. Margarita Hernandez and Jordi José), AIP Conf. Proc. 637,
299
In press :
An XMM-Newton study of 9Sgr and the Lagoon Nebula
Rauw, G.; Blomme, R.; Waldron, W.L.; Nazé, Y.; Harries, T.J.; Chapman, J.M.; Corcoran, M.F.; Detal, A.;
Gosset, E.; Pittard, J.M.; Pollock, A.M.T.; Runacres, M.C.; Sana, H.; Stevens, I.R.; Van Loo, S.; & Vreux,
J.-M., in New visions of the X-ray Universe in the XMM-Newton and Chandra Era, ESA SP-488, ed. F.
Jansen, in press
2. From the Liège team
Refereed journals :
Line profile variability in the spectra of Oef stars I. BD+60°2522
Rauw, G.; De Becker, M.; & Vreux, J.-M. 2003, A&A 399, 287
Optical spectroscopy of X-Mega targets - IV. CPD - 59°2636: a new O-type multiple system in the Carina
Nebula
Albacete Colombo, J.F.; Morrell, N.I.; Rauw, G.; Corcoran, M.F.; Niemela, V.S.; & Sana, H. 2002, MNRAS
336, 1099
The evolved early-type binary HDE 228766 revisited
Rauw, G.; Crowther, P.A.; Eenens, P.R.J.; Manfroid, J.; & Vreux, J.-M. 2002, A&A 392, 563
14
Phase-resolved X-ray and optical spectroscopy of the massive binary HD93403
Rauw, G.; Vreux, J.-M.; Stevens, I.R.; Gosset, E.; Sana, H.; Jamar, C.; & Mason, K.O. 2002, A&A 388, 552
An X-ray investigation of NGC346 field in the SMC (1): the LBV HD 5980 and the NGC 346 cluster
Nazé, Y.; Hartwell, J.M.; Stevens, I.R.; Corcoran, M.F.; Chu, Y.-H; Koenigsberger, G.; Moffat, A.F.J.;
Niemela, V.S.; 2002, ApJ 580, 225
Structure and Dynamics of Candidate O Stars Bubbles in N44
Nazé, Y.; Chu, Y.-H; Guerrero, M.A.; Oey, M.S.; Gruendl, R.A.; Smith, R.C. 2002, AJ 124, 3325.
Proceedings, various :
Line-Profile Variability in the Massive Binary System HD149404
Nazé, Y.; Carrier, F.; & Rauw, G. 2002,in Interacting Winds from Massive Stars, ASP Conference Series
260, eds. A.F.J. Moffat & N. St-Louis, 457
Optical Spectroscopy of Colliding-Wind Systems to be Observed with XMM Sana, H.; Rauw, G.; Gosset,
E.; & Vreux, J.-M. 2002, in Interacting Winds from Massive Stars, ASP Conference Series 260, eds. A.F.J.
Moffat & N. St-Louis, 431
Searching for Colliding-Wind Signatures in a Sample of O-Star Binaries
Rauw, G.; Sana, H.; Vreux, J.-M.; Gosset, E.; & Stevens, I.R. 2002, in Interacting Winds from Massive
Stars, ASP Conference Series 260, eds. A.F.J. Moffat & N. St-Louis, 449
V4741 Sagittarii
Gosset, E. 2002, IAU Circular 7887, 2.
Studying the X-ray properties of early-type stars
Vreux, J.-M.; & Rauw, G. 2001, in Space Scientific Research in Belgium, Vol II, Space Sciences, Part 1,
SSTC, 47
In press:
An X-ray investigation of the NGC 346 field in the SMC (2): the field population.
Nazé, Y.; Hartwell, J.M.; Stevens, I.R., Manfroid, J.; Marchenko, S.; Corcoran, M.F.; Moffat, A.F.J.;
Skalkowski,G.; ApJ in press
The wind of the B[e]Supergiant Hen S22 viewed through a reflection nebula in DEM L106
Chu, Y.-H; Chen, C.-H.R.; Danforth, C.; Dunne, B.C.; Gruendl, R.A.; Nazé, Y.; Oey, M.S.; Points, S.D.; AJ
in press
XMM-Newton high-resolution X-ray spectroscopy of the Wolf-Rayet object WR25 in the Carina OB1
association
Raassen, A.J.J.; van der Hucht, K.A.; Mewe, R.; Antokhin, I.I.; Rauw, G.; Vreux, J.-M.; Schmutz, W.; &
Güdel, M., A&A, in press
Monitoring the wind interaction in HD93403 with XMM-Newton
Rauw, G.; Vreux, J.-M.; Antokhin, I.I.; Stevens, I.R.; Gosset, E.; Sana, H.; Jamar, C.; & Mason, K.O., in
New visions of the X-ray Universe in the XMM-Newton and Chandra Era, ESA SP-488, ed. F. Jansen, in
press
Preliminary results from XMM-Newton observations of the massive WR+O binary WR22
Gosset, E.; Rauw, G.; Vreux, J.-M.; Nazé, Y. ; Antokhin, I.; Sana, H.; in A massive star odyssey, from Main
Sequence to Supernova, IAU Symposium 212, eds. K.A. van der Hucht et al., in press
15
Classification of NGC 595’s Wolf-Rayet stars population through high spatial resolution observations
Royer, P.; Lundstrom, I.; Vreux, J.-M.;
in A massive star odyssey, from Main Sequence to Supernova, IAU Symposium 212, eds. K.A. van der
Hucht et al., in press
Colliding Wind Binaries: an insight into O-star winds
Sana, H.; & Rauw, G., Revue des questions scientifiques, eds. G. Demortier & A. Lucas, in press
Massive Binaries and colliding winds
Rauw, G., EAS Publication Series, in press
Search of X-ray variability in early type stars in the Carina region with XMM-Newton
Antokhin, I.I.; Rauw, G.; Vreux, J.-M.; van der Hucht, K.;
in International Conference on Magnetic Fields in O, B and A stars, ASP Conference Series, in press
3. From the ROB team :
Refereed publications :
Blomme, R., Prinja, R.K, Runacres, M.C., Colley, S., 2003, Astron. Astrophys. 382, 921
Radio and submillimetre observations of ε Ori
Blomme, R., Runacres, M.C., 2002, in: Space Scientific Research in Belgium, Volume II Space Sciences, Part
1 (ed. SSTC-DWTC), 33
ISOPHOT Observations of Hot Stars
In press:
Blomme, R., Runacres, M.C., 2003, in: Proceedings of the "ISOPHOT Workshop on P32 Oversampled
Mapping", ESA-SP 482
Stellar winds of early-type stars
Blomme, R., 2003, in: Proceedings of IAU Symposium 210, “Modelling of Stellar Atmospheres”, (eds. N.E.
Piskunov, W.W. Weiss, D.F. Gray)
Structure in the Stellar Winds of O-type Stars
Blomme, R., 2003, in: Proceedings of IAU Symposium 215, “Stellar Rotation”, (eds. A. Maeder, Ph. Eenens)
Observational Effects of Corotating Interaction Regions in OB stars
Van Loo, S., 2003, in: Rev.Mex.AA (Serie de Conferencias). Ed. S. J. Arthur, W. J. Henney
Non-thermal radio emission from single hot stars
16
IV. Extragalactic Astrophysics and the
International Liquid Mirror Telescope
During the year 2002, the Liège team has been mainly involved in theoretical and observational studies of
quasars and gravitational lenses, the international 4m Liquid Mirror Telescope project and observations of
large scale structures in the Universe using the X-ray ESA Newton-XMM satellite. Most of these activities
have been carried out in the context of international collaborations (Canada, Chile, Denmark, France,
Germany, Greece, Holland, Italy, Norway, Spain, Ukraine and United States), including also scientists from
the Royal Observatory of Belgium (cf. collaborators whose names appear in the scientific publications).
IVa. Extragalactic Astrophysics
A new gravitational lens system, J1131-1231, has been discovered in May 2002 by our team. It is composed
of four macro-lensed images of a quasar surrounded by an optical Chwolson-Einstein ring. Several proposals
to re-observe this object under better conditions with the ESO Very Large Telescope (VLT), with the
Hubble Space Telescope (HST), with the Very Large Array (VLA) and with the Chandra X-ray Observatory
have been recently submitted. The redshift of the lensed quasar is z=0.65, corresponding to the nearest
cosmic mirage actually known. Collaborative work on this exciting target is presently taking place between
IAGL, ROB, ESO, University of Kiev, Imperial College of Science Technology and Medicine, University of
Hawaii.
Our team has also participated to the photometric monitoring and the lightcurve analysis of several multiply
imaged quasars among which the Einstein Cross 2237+0305 and UM673. These studies will contribute to an
independent determination of the Hubble constant via the measurement of time delays as well as to the
characterization of micro-lensing effects. ROB (Nakos et al.) has coordinated a project to establish a catalog
of secondary photometric standard stars around gravitational lenses; collaborators in this project are the
School of Physics and Astronomy of the Tel-Aviv University, the Skinakas Observatory (University of
Creta) and the National Observatory of Athens. The construction of the catalog was based on a long-term
monitoring of several GL-fields, for which the non-variable stars around each gravitationally lens system
were selected. With multiple observations under photometric conditions at Skinakas Observatory and at
SAAO the magnitudes of the non-variable stars were calibrated to the Johnson – Cousins photometric
system. ROB (Nakos et al.) and Liège astronomers have been working on photometric data of the GL
UM673. The data were obtained during the period 1998 – 2001 and consist of observations in the V and I
bands, performed with the 1.54 m Danish ESO telescope. The good time resolution (one week) and the two
filters will allow to detect any microlensing signature on the light-curve of each of the components, if not to
obtain the time delay for this system, given that there is a variability in the central engine of the host QSO.
Several independent methods for the analysis of the direct CCD images will be used.
Various studies of the intergalactic medium have been carried out using the spectra of background quasars
as light bulbs. These studies include the search for 105 to 107 K gas via the detection of the resonance OVI
absorption lines. We have estimated the size of Lyman- clouds from the statistical incidences and anticoincidences of Lyman- absorption lines detected in the spectra of multiply imaged quasars and/or distinct
nearby ones. Based upon HST observations, it has been possible to end a 20-year old-controversy about the
2 quasar images 2345+007 A and B which were thought to be those of a lensed quasar. The spectra obtained
by A. Smette and his American collaborators demonstrate that this is not the case: instead, the 2 images
originate from two different objects. Using the HST, we have also directly imaged the four known pairs of
nearby (< 5”) quasars with discordant redshifts in order to detect a secondary lensed image of the
background quasar near the foreground one. No such secondary images have been detected. We have
demonstrated that the four known pairs of nearby quasars essentially arise because of random projection
effects in the sky and that claims reported by Burbidge, Hoyle and Schneider on the unlikeness of these
quasar pairs are irrelevant. An efficient algorithm to deconvolve the spectra of very nearby quasars has been
17
developed and successfully used to study the multiply imaged quasar 1009-025 (collaboration with
University of Kiev). Studies of pairs of quasars with large angular separations (typically > 1’) have also been
performed. Several good gravitational lens candidates and/or quasars in distant clusters have been identified.
ESO VLT observing time has been granted to study these puzzling objects. This work is in progress. Several
review papers, as well as popular articles, on the subject of gravitational lensing have been published in
2002. Didactical experiments illustrating the formation of gravitational lens systems (multiple images,
Einstein ring and giant luminous arcs) have been presented at international conferences and during seminars.
The gravitational lens experiment is part of the 2000-2015 Cosmology exhibition taking place at the
National Air and Space Museum in Washington D.C. An exhaustive bibliography related to theoretical and
observational studies of gravitational lenses in the form of a public database (totaling more than 3000 titles)
as well as the physical characteristics and direct images of all known gravitational lens systems has been set
up on the web page :
http://vela.astro.ulg.ac.be/grav_lens/grav_lens.html. This database is very frequently used by scientists from
the astronomical community at large. More than 30.000 entries have been registered.
Various programs of observations of active galactic nuclei, quasars and high redshift galaxy clusters by
means of the present XMM and future COROT and GAIA space observatories are underway or have been
proposed. In this context, Th. Nakos who has just taken up a two-year student position at ESO, is now
involved in the data reduction of NIR data related to the XMM-LSS project (see the URL:
http://vela.astro.ulg.ac.be/xmm/LSS). One of the main goals of the LSS consortium is to probe the evolution
of the Universe by studying distant (i.e. faint) QSOs. NIR observations will help us to conduct a new QSO
catalog by cross-correlating X-ray and NIR data. Regarding GAIA, it is a planned ESA mission to determine
distances and proper motion of up to 1 billion stars in our Galaxy, the Milky Way. As a by-product, it will
also detect 500,000 quasars and of the order of 2,000 gravitational lens systems. Several scientists from
IAGL are involved in these studies. Finally, gamma-ray bursters were initially revealed by their short but
intense bursts of gamma-rays, a high energy radiation which, fortunately, is stopped by the Earth's
atmosphere. Although a lot of progress has been made in their understanding since their discovery about 30
years ago, their precise origin is still unknown, although they appear linked to the explosion of very massive
and therefore young stars. HST studies in which some of us take part tend to confirm this hypothesis by
showing that gamma-ray bursts occur in galaxies showing a large amount of star formation.
Th. Nakos (ROB and Ulg) coordinated a project to establish a catalog of secondary photometric standard stars
around gravitational lenses; collaborators in this project are the School of Physics and Astronomy of the TelAviv University (Israel), the Skinakas Observatory (University of Creta, Greece) and the National Observatory
of Athens (Greece). The construction of the catalog was based on a long-term monitoring of several GL-fields,
for which the non-variable stars around each gravitationally lensed system were selected. With multiple
observations under photometric conditions at Skinakas Observatory and at SAAO the magnitudes of the nonvariable stars were calibrated to the Johnson – Cousins photometric system. This project is ended and a paper
has been submitted to Astronomy & Astrophysics.
Th. Nakos with F. Courbin (Institute of Astrophysics, University of Liège) have been working on
photometric data of the GL UM673. The data were obtained during the period 1998 – 2001 and consist of
observations in the V and I band, performed with the 1.54 m Danish ESO telescope. The good time
resolution (one week) and the two filters will allow to detect any microlensing signature on the light-curve
of each of the compoments, if not to obtain the time delay for this system, given that there is a variability in
the central engine of the host QSO. Th. Nakos has been using the so-called MCS method, which is a
deconvolution method developed by one of the groups in Liège working on extra-galactic astrophysics.
By the start of his two-year stay at Santiago, as an ESO student, Th. Nakos is now involved in the data
reduction of NIR data related to the XMM-LSS project. One of the main goal of the LSS consortium is to
probe the evolution of the Universe by studying distant (i.e. faint) QSOs. NIR observations will help us
conduct a new QSO catalog by cross-correlating X-ray and NIR data.
18
IVb. International Liquid Mirror Telescope (ILMT) project
The great scientific motivation to use a telescope dedicated to the photometric monitoring of multiply
imaged quasars (gravitational lens systems) has led us to assess the expected performances of a liquid mirror
telescope. In collaboration with scientists and engineers from the Liège Space Center (locally known as
CSL), from the industrial company AMOS (Advanced Mechanical and Optical Systems) and from multiple
international research institutions, the Royal Observatory of Belgium (ROB) and the Liège Institute of
Astrophysics and Geophysics Institute (IAGL) are presently involved in the construction of a 4m liquid
mirror telescope (known as the International Liquid Mirror Telescope project) which should be erected in
Chile in 2004-2005. The main goal is to daily monitor a narrow strip of sky (half a degree wide) near the 29declination down to the magnitude B = 24. This survey will approximately cover a field of 100 square
degrees at high galactic latitude (bII 30). We have estimated that more than 50 multiply imaged quasars
should be photometrically monitored every night. Some 50 cases of micro-lensing effects taking place in our
own Galaxy should also be detected every year. The stacking of all CCD frames recorded during the span of
one year should also lead to the detection of some 50 giant luminous arcs. The lightcurves recorded for the
multiple point-like images of the macro-lens systems will significantly contribute to an independent
determination of the Hubble constant and to observational studies of extragalactic micro-lensing effects.
These systems will constitute unique targets for subsequent observational studies with the VLT and ALMA.
Publications (from the Liège group)
Published papers :
Alcalde, D., Mediavilla, E., Moreau, O., Munoz, J.A., Libbrecht, C., Goicoechea, L.J., Surdej, J., Puga, E.,
De Rop, Y., Barrena, R., Gil-Merino, R., Mc Leod, B.A., Motta, V., Oscoz, A., Serra-Ricart, M.: 2002,
"QSO 2237+0305 V R light curves from GLITP optical monitoring'' Astrophys. J. 572, 729-734
Aracil B., P. Petitjean, A. Smette, J. Surdej, J.P. Mucket, and S. Cristiani: 2002, "Extension of Lymanalpha Complexes from HST Observations of Four Pairs of Quasars", Semaine de l'Astrophysique Francaise,
meeting held in Paris, France, June 24-29, 2002, Eds.: F. Combes and D. Barret, EdP-Sciences (Editions de
Physique), Conference Series.
Aracil, B., Petitjean, P., Smette, A., Surdej, J., Mücket, J., Cristiani, S.: 2002, "HST STIS observations of
four QSO pairs'', Astron. Astrophys. 391, 1-12.
Burud i., A. Fruchter, J. Rhoads, A. Levan and A. Smette et al. : 2002, "GRB020322 : HST/STIS
observations", GCN 1536, 1.
Claeskens, J.-F., Surdej, J.: 2002, “Gravitational Lensing in Quasar Samples”, Astron. & Astrophys.
Review, 10, 263-311, electronic access via the URL:
http://link.springer.de/link/service/journals/00159/first/bibs/s001590000010.htm
Claeskens, J.-F., Jean, C., Surdej, J.: 2002, in "Microlensing observations with the 4m International Liquid
Mirror Telescope (ILMT)", the proceedings of the Conference "Microlensing 2000: A New Era of
Microlensing Astrophysics'', Eds. Menzies, J.W., Sackett, P.D., ASP Conference Series, Vol. 239, pp. 373377.
Claeskens, J.-F., Gosset, E., Smette, A., Surdej, J.: 2002, "Photometric variability of QSOs and Active
Galactic Nuclei with COROT'', paper to be published in the proceedings of the ``Corot Scientific Week
No2'' organized in Meudon, 13-16 May 2001''; the proceedings will soon become available on the site:
http://www.astrsp-mrs.fr/projets/corot/meeting/CW2.html
19
Fruchter A., J. Rhoads, I. Burud, A. Levan, S. Patel, C. Kouveliotou, J. Gorosabel, J. Hjorth and A.
SMETTE et al. "The probable host galaxy of GRB/XRF 020427" : 2002, GCN 1440, 1.
Fruchter A., S. A. J. Levan, I. Burud, P. E. Nugent and A. Smette et al.: "GRB 020410: discovery of
probable OT by HST" 2002, GCN 1453, 1.
Fruchter A., A. Levan, P. Vreeswijk, S. T. Holland, C. Kouveliotou and A. Smette et al.: 2002, GC"GRB
021211: probable host and underlying supernova", N 1781, 1.
Fruchter A., S. Pattel, C. Kouveliotou, J. Rhoads, S. Holland, I. Burud, R. Wijers and A. SMETTE et al.:
2002, "XRF/GRB 011030: detection of the probable host galaxy", GCN 1268, 1.
Gorosabel J., J. Fynbo, I. Burud, A. Fruchter, J. Hjorth and A. Smette et al.: 2002, "GRB 020305:
HST/STIS observations", GCN 1542, 1
.
Khmil, S.V., Surdej, J.: 2002, "Optimal extraction of multiple overlapping spectra using a maximum entropy
algorithm"? Astron. Astrophys. 387, 347-355.
Levan A.J., A. S. Fruchter, I. Burud, J. E. Rhoads and A. Smette et al. : 2002, "GRB 020813 : HST
observations", GCN 1518, 1.
Levan A. , A. Fruchter, L. Strolger, I. Burud, J. Rhoads and A.Smette et al.: 2002, "XRF 020903 : HST
observations" GCN 1761, 1.
Reipurth B., L. Hartmann, S. J. Kenyon, A. Smette, and P. Bouchet: 2002, "Evolution of the Fu Orionis
Object BBW 76", AJ 124, 2194-2206.
Sahu K., A. Fruchter, I. Burud, K. Sembach and A. Smette et al.: 2002, "GRB 021004: HST/STIS
spectroscopic observations", GCN 1608, 1.
Sluse, D., Surdej, J., Claeskens, J.F., De Rop, Y., Lee, D.-W., Iovino, A., Hawkins, M.: 2002, "Close pairs
of quasars with different redshifts : New observations and results'' Astron. Astrophys. 397, 539-544.
Surdej, J., Claeskens, J.-F.: 2002, "Gravitational Lensing'' chapter for the book 'The Century of Space
Science', Eds. J. Bleeker, J. Geiss & M.C.E. Huber, Kluwer Academic Publishers, 441-469.
Vangeyte, B., Manfroid, J., Surdej, J.: 2002, "Study of CCD mosaic configurations for the ILMT: astrometry
and photometry of point sources in the absence of a TDI corrector'', Astron. Astrophys. 388, 712-731.
Zhdanov, V.I., Surdej, J.: 2002, "Physical grouping of quasars from the Véron-Cetty & Véron and 2dF QSO
catalogs'', Paper published in the proceedings of the workshop ``Visnik Kyivskogo Universitetu (Messenger
of Kiev University)'' organized in Kiev (May 2001)
In press :
Sluse, D., Surdej, J., Claeskens, J.-F., Courbin, F., Hutsemekers, D., Jean, C., Billeres, M., Khmil, S.: 2002,
"A quadruply imaged quasar with an optical Einstein ring candidate: 1RXJ113155-123155", A & A Letter,
submitted
Sluse, D., Surdej, J., Claeskens, J.-F., Hutsemekers, D., Jean, C., Khmil, S.: 2003, "Discovery of a new
quadruply imaged quasar surrounded by a ring", Proceedings of Aussois 2003 meeting: Gravitational
Lensing : a Unique Tool for Cosmology, in press.
20
V. ESO's Very Large Telescope Interferometer (VLTI) &
Astrophysical Studies at Very High Angular Resolution
An important instrumental project in the context of high angular resolution observations of faint objects (cf.
exo-zodi, exo-planets) located very near a bright point-like source (cf. the host star) has been carried out at
IAGL (PhD work of O. Absil). This research has been mainly focused on the pre-phase A design of the
Ground-based European Nulling Interferometer Experiment (GENIE), in collaboration with the European
Space Agency and the European Southern Observatory. A software has been built to simulate future GENIE
observations, taking into account all noise sources including the effect of atmospheric turbulence and
thermal background emission. The control of OPD, dispersion and intensity are very critical for the
operation of a ground-based nulling interferometer, and has been tackled thoroughly. Advanced chopping
methods have also been investigated. In the context of GENIE, several research projects are under
development. One of these is the subject of the PhD thesis of O. Absil. It concerns the detection of
circumstellar dust clouds, especially around Vega-type stars and Young Stellar Objects. Test observations
with the CHARA/FLUOR interferometer, in collaboration with V. Coudé du Foresto (Observatoire de ParisMeudon) are under way. These preparatory observations for GENIE could give some preliminary
information on the hot dust surrounding main-sequence stars. Besides GENIE, work on the optimization of
the aperture configurations for the DARWIN interferometer has also been carried out at IAGL. New
configurations have been proposed to reduce the complexity of the optical recombination scheme while
improving the sensitivity of the interferometer.
Additional activities in the field of high angular resolution astrophysics also involve the study of innovating
Achromatic Phase Shifters (PhD work of D. Mawet). The latter are mandatory components in the field of
nulling interferometry (cf. GENIE) and phase coronagraphy. Indeed, in order to detect faint objects (cf. exoplanets, for instance) around a central bright target (cf. host star), one must attenuate it by all means. To do
this, the most efficient way is to “create” a destructive interference on the light coming from the blinding
star. This technique is known as “nulling” and is common to the two fields mentioned above; the first with
several telescopes, the second with only one aperture. How does it work? The incoming light from the
central object is divided in several beams over which one applies a differential phase shift. This operation
result in changing the sign of, for instance, one of the two beams by means of a so-called phase shifter.
Then, when we properly recombine the separate beams together, they simply subtract from each other!
Achromatic means that we can apply this process over a large spectral bandwidth (range of colours). This
quality is required for the detection and characterisation of exo-planets. Innovating APSs consist of
subwavelength structures, i.e. imprinted on a scale smaller than the wavelength of the incident light (1/10
microns for the infrared for instance). These structures are seen by the incident light as a homogeneous
medium with very specific and amazing properties one can play with to design flexible APSs. The
implementation on interferometers (DARWIN) and coronagraphs (Four Quadrant Coronagraph) of such
components is under study by our team. Some success has already been encountered. Indeed, the first
Achromatic Four Quadrant Phase Mask will soon be tested. The latter is not composed of subwavelength
structure which are very costly but directly profits from recent researches on this subject.
Publications
Papers in press or submitted :
Absil, O. : 2003, "GENIE: a ground-based precursor for the IRSI-Darwin mission", in "Astronomy with
High Contrast Imaging: From Planetary System to Active Galactic Nuclei", EAS publication series, in press.
Absil O, P. Gondoin, R. den Hartog, C. Erd, M. Fridlund, L. Labadie, N. Rando, V. Coudé du Foresto:
2003, "Candidate VLTI configurations for the GENIE nulling experiment", proceedings of "Scientific
Frontiers in Research on Extrasolar Planets", June 2002, Washington, to be published in ASP Conf. Series.
21
Absil O., P. Gondoin, R. den Hartog, C. Erd, M. Fridlund, N. Rando: 2003, "The GENIE nulling
experiment", proceedings of the "Semaine de l'Astrophysique Française", Paris, June 2002, to be published
by EDP Sciences.
Absil O, V. Coudé du Foresto: 2003, "Influence of optical path delay control on a ground-based nulling
interferometer", Proc. SPIE, vol. 4838, in press.
Absil O., A. Karlsson, L. Kaltenegger: 2003, "Inherent modulation: a fast chopping method for nulling
interferometry", Proc. SPIE, vol. 4852, in press.
Mawet D., C. Lenaerts, V. Moreau, Y. Renotte, D. Rouan, J. Surdej: 2003, "Achromatic Four Quadrant
Phase Mask using the Dispersion of Form Birefringence", Proc. of SPIE 2002, in press.
Mawet D., C. Lenaerts, V. Moreau, Y. Renotte, D. Rouan, J. Surdej: 2003, "Achromatic four quadrant phase
mask coronagraph using the dispersion of form birefringence", Astronomy with High Contrast Imaging,
EAS Publications Series, in press.
22
VI. Additional Topic
Research on evolved stars with debris disks
Greet DECIN, K.U. Leuven, has continued her research on stars for which infrared excesses discovered by
IRAS point toward the presence of dusty debris disks:
-
-
For the G-type main-sequence stars for which debris disks were discovered, abundance analyses were
made from spectra obtained with the CORALIE spectrograph on the Leonhard Euler Telescope at La
Silla Observatory. It turns out that on average the debris disk objects present a subsolar metallicity, i.e.
a trend which is opposite to that observed in G dwarfs for which planets have been detected.
For the K-giants it now appears that the IRAS excesses are due to genuine debris disks in at most a few
cases, and that for most objects they probably are due to illumination of interstellar cirrus.
Attendance by Greet DECIN of foreign conferences, meetings, …:
27 March. Interstellar and Circumstellar Matter Meeting, Amsterdam, NL
11-13 April. ‘Debris Disks and Planetary Formation: A Symposium in
Memory of Fred Gillett’, Tucson, Arizona, USA
26 June. Discussion meeting with Dr. C. Dominik, Amsterdam, NL
23
ANNEX 1
Ph.D Dissertations (IAP Themes)
a) at the KU Leuven
June 25, 2002
Katrien KOLENBERG
"A Spectroscopic Study of the Blazhko Effect in RR Lyrae"
October 4, 2002
Kristin REYNIERS
"Tidal perturbations of linear, isentropic oscillations in components of circular-orbit close binaries"
December 20, 2002
Maarten REYNIERS
"High Resolution Spectroscopy of Post-AGB Stars: AGB Nucleosynthesis and Dredge-up"
b) at Ulg
May 8, 2002
Geneviève PARMENTIER
Self-enrichment and formation of galactic halo globular clusters
December 16, 2002
Marc-Antoine DUPRET
"Non-radial non-adiabatic oscillations of near main sequence variable stars"
January 28, 2003
Elisa DI PIETRO
"Modèles cosmologiques de quintessence et supernovae de type Ia"
March 12, 2003
Marilyne BRIQUET
"An observational study of line-profile variable B stars"
24