BAG workshops - Département d'Astrophysique, Géophysique et ...

This TD includes the following Sections: ...... remaining period along with all expenses incurred by the bank for renovation of its branch at the demised premises.

part of the document

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:
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.
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...
Extract from the synthetic spectra the frequencies and splittings with their formal errors leading to an "observed" set of frequencies.
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 stars 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 INCLUDEPICTURE "http://www.astro.ulg.ac.be/PAI/gifs/beta.gif" \* MERGEFORMATINET 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 observations were collected with the FEROS spectrograph during 2001-2002, which brings the total number of spectra above 130, while the last lightcurve data from the SAT rounded 1200 in the year 2003. The time-series spectroscopy shows profound LPVs in the single-lined spectrum due to the pulsations in the ( Cephei and we find indications of three pulsation frequencies in the radial-velocity data. Because radial velocities (RVs) from spectral lines were strongly affected by line-profile variations (LPVs), a novel method was developed to measure the orbital RVs. By matching pairs of spectra with similar LPV patterns and cross-correlating them, it was possible to get RV differences across the full orbital phase. With a software routine designed by our Croatian collaborators, a Keplerian eccentric orbit was then iteratively optimised to fit the RV differences. This approach significantly reduced the influence of the LPVs on the orbital solution and resulted in an improved orbital period, a small, but significant, eccentricity (e=0.03), and stellar masses of 15 M( and 3 M( with corresponding radii of 8.3 R( and 2.1 R(, and temperatures of 25500 and 12500 K. The orbital and dimensional analysis has been concluded. Then the orbital imprint has been removed from the spectra and the light curves (with more out-of-eclipse observations added). We have attempted to detect the secondary spectrum and to identify the pulsation modes. Finally, an asteroseismological analysis has been performed in order to gain insight into the stellar structure and other physical properties of the pulsating star. A full dynamical analysis of the binary was also performed. We find stellar dimensions of 15 and 3 solar masses, radii of 8.4 and 2.1 solar radii and temperatures of 25500 and 12500 K for the bright B1III and faint B7-B9V components. The major limitation is the absence of a secondary spectrum. A search for line-profile variations in all lines in the wavelength region from H-alpha to H-epsilon indicated that about 30 lines contain significant pulsational information. It was demonstrated that by combining power spectra across more lines, the detection of oscillation frequencies was enhanced significantly. We are now performing a pulsational analysis of the 103 FEROS spectra with the purpose of identifying modes of two or all three known oscillation frequencies.

HD 129929 - We have gathered and analysed a timeseries of 1493 high-quality multicolour Geneva photometric data of the B3V ( Cep star HD 129929. The dataset has a time base of 21.2 years. The occurrence of a beating phenomenon is evident from the data. We find evidence for the presence of at least six frequencies, among which we see components of two frequency multiplets with an average spacing of ~0.0121 cd-1 which points towards very slow rotation. This result is in agreement with new spectroscopic data of the star and also with previously taken UV spectra. We provide the amplitudes of the six frequencies in all seven photometric filters. The metal content of the star is Z = 0.018 ± 0.004. We then performed a detailed seismic study of the ( Cep star HD 129929. Our analysis is based on the recent derivation of six pulsation frequencies. These frequencies are unambiguously identified from the seismic modelling and the photometric amplitudes to be the radial fundamental, the l = 1, p1 triplet, two consecutive components of the l = 2, g1 quintuplet. A non-adiabatic analysis allows us to constrain the metallicity of the star to Z INCLUDEPICTURE "http://www.astro.ulg.ac.be/PAI/gifs/epsilon2.gif" \* MERGEFORMATINET [0.016,0.022]. In addition, the fitting of three independent frequencies, two of which correspond to axisymmetric (m = 0) modes, allows us to constrain the core overshooting parameter to INCLUDEPICTURE "http://www.astro.ulg.ac.be/PAI/gifs/alpha.gif" \* MERGEFORMATINET OV = 0.10 ± 0.05, as well as the other global parameters of the star. Finally, from the observation of the l = 1 triplet and part of the l = 2 quintuplet, we derive constraints on the internal rotation of this star. This breakthrough was published in Science and in two A&A papers and constituted the topic of a documentary in the series Overleven and Matière Grise broadcasted by VRT and RTBF televisions in 2005.

3) B and SPB stars
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.
He and Si surface inhomogeneities of four B variable stars - We present ground-based multi-colour Geneva photometry and high-resolution spectra of four variable B-type stars: HD 105382, HD 131120, HD 138769 and HD 55522. All sets of data reveal monoperiodic stars. A comparison of moment variations of two spectral lines, one silicon line and one helium line, allows us to exclude the pulsation model as being the cause of the observed variability of the four stars. We therefore delete the four stars from the list of candidate of slowly pulsating B stars. We attribute the line-profile variations to non-homogeneous distributions of elements on the stellar surface and we derive abundance maps for both elements on the stellar surface by means of the Doppler Imaging technique. We confirm HD 131120 to be a He-weak star and we classify HD 105382, HD 138769 as new He-weak stars. HD 55522 has the solar helium abundance but the mean abundance value of He varies by 0.8 dex during the stellar rotation. For HD 131120 and HD 105382, helium is enhanced in regions of the stellar surface where silicon is depleted and depleted in regions where silicon is enhanced.
Mode identification for a sample of SPB stars - We obtained results of the mode identification for a sample of 7 bright southern slowly pulsating B stars showing one pulsation frequency in the 413 nm Si II profiles. We combined the results from (1) the method of photometric amplitudes; (2) the moment method; and (3) the amplitude and phase variation across the profile to search for the l and m values of the modes best fitting the data. It is the first time that the applicability of these techniques is tested to a sample of main-sequence g-mode pulsators. Combining the moment method with the amplitude and phase variations across the observed line profile gives an improvement in spectroscopic identification of low degree l g-mode pulsations. Using the variations of the higher order even moments < v4> and < v6> of the moment method solutions can also help. For HD 181558, HD 24587, HD 140873 and HD 177863, the photometric and spectroscopic results are compatible and point towards (l,m) = (1, +1) sectoral modes. For HD 215573, HD 53921 and HD 92287, the results are inconclusive.
Application of spectral disentangling to slowly pulsating B stars (SPB) in binaries - We want to investigate: (1) to which extend current disentangling codes can be used for systems containing a pulsating component, (2) if the results of the pulsation analysis can be improved by first subtracting the contribution of the non-pulsating components from the spectra. Our investigation is based on observed high-resolution spectra of HD 140873 and HD 123515 obtained with the CAT/CES combination at La Silla in 1996-1998, and on synthetic data. HD140873 and HD123515 are both non-eclipsing double-lined binaries in eccentric orbits of 39 and 26 days. The broad-lined primary of HD140873 is an apparently monoperiodic SPB, while the sharp-lined primary of HD123515 is a multiperiodic SPB prototype. The spectral disentangling seems to be working fine in the case of HD140873. After removal of the secondary from the data, we re-analyzed the pulsations of the primary, which leads to a better agreement in the temporal behavior of the two SiII profiles. For HD123515, spurious features appear in the disentangled component spectrum for the secondary. We suspect that these features are induced by the pulsations of the primary, which is supported by the tests we did so far with similar synthetic data sets. However, more tests on synthetic data are needed to understand under which conditions the disentangling of the component spectra is applicable to binaries with a SPB component. Presently, two IAP partners are involved in this study.
4) ( Scuti and ( Doradus stars
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.
Theoretical instability strips for ( Scuti and ( Doradus stars - New theoretical instability strips for ( Sct and ( Dor stars are presented. These results have been obtained taking into account the perturbation of the convective flux following the treatment of Gabriel (1996). For the first time, the red edge of the ( Sct instability strip for non-radial modes is obtained. The influence of this time-dependent convection (TDC) on the driving of the ( Dor gravity modes is investigated. The results obtained for different values of the mixing-length parameter ( are compared for the ( Dor models. A good agreement with observations is found for models with ( between 1.8 and 2.0.
( Doradus stars - We have reported on our results from a large photometric campaign on thirty five INCLUDEPICTURE "http://www.astro.ulg.ac.be/PAI/gifs/gamma.gif" \* MERGEFORMATINET 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 ( 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. We apply for the first time the time-dependent convection (TDC) treatment of Gabriel and Grigahcène et al. to the photometric mode identification in ( Doradus stars. We consider the influence of this treatment on the theoretical amplitude ratios and phase differences. Comparison with the observed amplitudes and phases of the stars gamma Dor, 9 Aurigae, HD 207223 = HR 8330, HD 12901 and 48501 is presented and enables us to identify the degree l of the pulsation modes for four of them. We also determine the mode stability for different models of these stars. We show that our TDC models agree better with observations than with frozen convection models. Finally, we compare the results obtained with different values of the mixing-length parameter alpha.
DG Leo: a triple system containing a ( Scuti star - DG Leo is a hierarchical triple with all three components situated in the ( Scuti instability strip. Previously, we showed that it consists of a close binary with two mild Am stars, and a INCLUDEPICTURE "http://www.astro.ulg.ac.be/PAI/gifs/delta.gif" \* MERGEFORMATINET Scuti type wide companion showing multi-mode line-profile variability. The system puts empirical constraints on the development of pulsations in stars of the same mass and age, but with different internal structure that provokes different chemical composition in the outer layers. In 2004, a detailed abundance analysis confirming the enhanced metallicity in the close binary and solar abundances in the wider component was performed and published.
5) Solar type stars
( Cen - Models of ( Cen A & B have been computed using constraints obtained from global properties as well as from seismological data. We have shown that seismological constraints 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.
6) Variable stars in clusters
Variable stars in star clusters share common ages, original chemical composition and distance, which strongly simplifies the comparison with theoretical models. We take advantage of this when studying pulsating variables in the globular cluster ( Centauri (though metal abundance is a free parameter in this case). This results from a collaboration between two of the IAP partners and colleagues in Rome (OAR), Germany (AIP) and Denmark (CUAO), and in a second project where we search for open clusters well suited for multi-site campaigns of ( Sct stars.
( Centauri - A photometric investigation is carried out on ( Centauri with the final purpose of detecting and studying variables (in particular SX Phe stars suitable for asteroseismology), and to study the complex evolution history of this cluster. The observational basis is FORS observations (Chile, Paranal) obtained at high angular resolution (seeing better than 0.3 arcseconds), about 5000 times series points from the Danish 1.5 meter (optical, La Silla), the 3.5 meter NTT (near-infrared, La Silla) and observations from the ESO archive (optical/near-infrared, WFI/2.2m, HST, VLT). Due to ( Cen's uniquely large spread in chemical abundances, 3-4 separate red giant branches have been discovered in the last 6 years. One of these branches deviates strongly from the bulk of the cluster stars and the origin for the stars in this branch is particularly puzzling as they appear to be chemically and kinematically different from the rest of the cluster stars. Based on optical (VLT and HST) and NTT (near-infrared) data, we suggest, by comparing observations with stellar evolutionary models, that this branch and a newly discovered sub-giant branch can be described altogether as a clump of the cluster's stars positioned 500 pc beyond ( Cen. If confirmed, this supports other indications of presence of a cluster tidal tail, typical for captured dwarf galaxies. Our separate study of deep hst-Acs photometry resu1ted in the detection of the largest known population ever of white dwarfs (WDs) exceeding 2000 such objects. We find this sample in agreement with predictions based on the ratio between WDs and Horizontal Branch evolutionary lifetimes.
NGC 1817 - With the Nordic Optical Telescope (NOT, Canary Islands), selected northern open star clusters are examined for their content of short-period variables of the types ( Scuti and ( Cephei, currently the most successful classes of variables applied in asteroseismic tests. Photometry of clusters with several of such variables inside convenient field-of-views is then followed up by spectroscopic studies, and photometric multi-site campaigns, which is particularly feasible on the northern hemisphere. The current cluster monitored with the NOT, NGC 1817, was a cluster already known to host 7 potential ( Scuti stars, and in collaboration between the two IAP partners in Brussels and Aarhus University (Denmark, IfA), 5 nights in December 2002, were used to collect time-series observations in B and V as well as uvby standard data. Preliminary results from the analysis of these observations announced the detection of 14 new variable stars in the cluster. This brings the total number of known variable stars in NGC 1817 up to 19, including 12 multi-periodic ( Scuti stars. In one case, a INCLUDEPICTURE "http://www.astro.ulg.ac.be/PAI/gifs/delta.gif" \* MERGEFORMATINET Scuti star is also member of an eclipsing binary system, which is valuable for obtaining precise, independent stellar parameters. Calibration of the broadband photometry is now almost finished and is used to confirm the location of the new variables inside the ( Scuti instability strip, while the standardisation of the uvby data is still in progress. The open cluster studies run in three stages on more clusters: 1) identification of clusters hosting several short-period variables, 2) through uvby photometry and spectroscopy derive physical stellar parameters required for selection of variables suitable for seismic analysis, and 3) a multi-site campaign on the cluster variables in order to reduce the power of alias frequencies in frequency analysis.
7) A and F stars
First results of Mercator observations - The Mercator telescope is a 1.2 meter telescope located on the Roque de los Muchachos observatory on La Palma, Spain. The scientific observations started in spring 2001. Since 2001, the telescope has been intensively used to observe pulsating B, A, and F main sequence stars. We have at present 31 data sets of A and F stars, containing mainly ( Doradus stars and 28 data sets of B stars. All data sets were subjected to an extensive frequency analysis, where objectivity was imposed by having each star independently analysed by two or three researchers. The frequency analysis was done with the PDM method and with the Lomb-Scargle method. We find that most stars are clearly multiperiodic. From these results, the most promising targets have been selected for long-term monitoring. Overview talks of the Mercator results will be presented at the JENAM 2005 Meeting in Liège.
8) Non-adiabatic analysis
We present an improved version of the method of photometric mode identification of Heynderickx et al.. Our new version is based on the inclusion of precise non-adiabatic eigenfunctions determined in the outer stellar atmosphere according to the formalism recently proposed by Dupret et al.. Our improved photometric mode identification technique is therefore no longer dependent on ad hoc parameters for the non-adiabatic effects. It contains the complete physical conditions of the outer atmosphere of the star, provided that rotation does not play a key role. We apply our method to the two slowly pulsating B stars HD 74560 and HD 138764 and to the ( Cephei star EN (16) Lac. Besides identifying the degree l of the pulsating stars, our method is also a tool for improving the knowledge of stellar interiors and atmospheres, by imposing constraints on parameters such as the metallicity and the mixing-length parameter ( (a procedure we label non-adiabatic asteroseismology).
9) Spectroscopic analysis
Spectroscopic analysis of pulsating stars - We implemented a new version of the moment method to identify modes of pulsating stars from high-resolution spectroscopy. This new version is generalised to rotating stars and is more appropriate to multiperiodic stars than any of the other methods available so far. We have applied the new method to several pulsating B stars and will continue to do so in the near future.
4. Position of the IAP Asteroseismology Network
4.1 Cutting edge research
We repeat that the Belgian Asteroseismology Group (BAG, http://www.asteroseismology.be) 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 2006 and lifetime of about two years. Several members of the BAG are involved in the development of these missions. Currently the BAG consists of 35 Belgian scientists. The example of the BAG has given rise to the creation of a similar network at the European level (ENEAS see below).
4.2 International role
The European Network of Excellence in AsteroSeismology (ENEAS) was created on 11 October 2002 during a kick-off meeting held in Leuven (Belgium) at the initiative of the Belgian Asteroseismology Group. The purpose of ENEAS is to provide an efficient coordination between the numerous, already existing European initiatives in asteroseismology and to achieve an effective integration of all European expertise in this research domain through numerous exchanges of the ENEAS scientists. Another prime goal of ENEAS is to prepare European scientists for the huge databases of seismic data of stars that will be delivered by European space missions, such as CoRoT, in the near future. Any information on ENEAS can be found at the ENEAS web page: HYPERLINK "http://www.eneas.info" http://www.eneas.info. This web page will gradually include more and more applications, such as basic information about ENEAS, databases of seismic observations, a database of analysis tools with user-guidelines, outreach material, asteroseismology courses etc. Besides this electronic communication channel, we will publish any ENEAS matters in the journal Communications in Asteroseismology under editorship of M. Breger (Vienna University). Presently, 256 scientists from 43 institutes are members of ENEAS.

4.3 Durability of the IAP

We hope it is clear from this report that the scientific pole on Asteroseismology has acquired the largest critical mass in Belgian astronomy. We have also shown that this has given rise to scientific results of the highest possible level as illustrated by the paper published in the prestigious journal Science. It is therefore evident that we request future funds to continue and intensify our activities and collaborations in the next 5 years.

5. Output

5.1 IAP Publications

During the current IAP, about 30 international refereed papers with common authors from the different Institutes have been published within the BAG. Below we only list ten of them.

Asteroseismology of HD 129929: core overshooting and nonrigid rotation   C. Aerts, A. Thoul, J. Daszynska, R. Scuflaire, C. Waelkens, M.-A. Dupret, E. Niemczura, A. Noels, 2003, Science, 300, 1926-1928

Asteroseismology of the INCLUDEPICTURE "http://www.astro.ulg.ac.be/PAI/gifs/beta.gif" \* MERGEFORMATINET Cephei star INCLUDEPICTURE "http://www.astro.ulg.ac.be/PAI/gifs/nu.gif" \* MERGEFORMATINET Eridani: Massive exploration of standard and non-standard stellar models to fit the oscillation data    M. Ausseloos, R. Scuflaire, A. Thoul, C. Aerts, 2004, Month. Not. R. Astron. Soc., 355, 352-358

Long-term multicolour photometry and high-resolution spectroscopy of the two INCLUDEPICTURE "http://www.astro.ulg.ac.be/PAI/gifs/gamma.gif" \* MERGEFORMATINET Doradus stars HD 12901 and HD 48501C. Aerts, J. Cuypers, P. De Cat, M.-A. Dupret, J. De Ridder, L. Eyer, R. Scuflaire, C. Waelkens, 2004, A&A, 415, 1079-1088.

Influence of non-adiabatic temperature variations on line profile variations of slowly rotating INCLUDEPICTURE "http://www.astro.ulg.ac.be/PAI/gifs/beta.gif" \* MERGEFORMATINET Cep stars and SPBs. I. Non-adiabatic eigenfunctions in the atmosphere of a pulsating starM.-A. Dupret, J. De Ridder, C. Neuforge, C. Aerts, R. Scuflaire, 2002, A&A, 385, 563-571

Seismic modelling of the INCLUDEPICTURE "http://www.astro.ulg.ac.be/PAI/gifs/beta.gif" \* MERGEFORMATINET Cep star EN (16) LacertaeA. Thoul, C. Aerts, M.-A. Dupret, R. Scuflaire, S.A. Korotin, I.A. Egorova, S.M. Andrievsky, H. Lehmann, M. Briquet, J. De Ridder, A. Noels, 2003, A&A, 406, 287-292

A study of bright slowly pulsating B stars. III. Mode identification for singly-periodic stars in spectroscopyP. De Cat, M. Briquet, J. Daszynska-Daszkiewicz, M.-A.Dupret, J. De Ridder, R. Scuflaire, C. Aerts, 2005, A&A, in press

A photometric mode identification method, including an improved non-adiabatic treatment of the atmosphere    M.-A. Dupret, J. De Ridder, P. De Cat, C. Aerts, R. Scuflaire, A. Noels and A. Thoul, 2003, A&A, 398, 677-685
Asteroseismology of the INCLUDEPICTURE "http://www.astro.ulg.ac.be/PAI/gifs/beta.gif" \* MERGEFORMATINET Cep star HD 129929. I. Observations, oscillation frequencies and stellar parameters.
C. Aerts, C. Waelkens, J. Daszynska-Daszkiewicz, M.-A. Dupret, A. Thoul, R. Scuflaire, K. Uytterhoeven, E. Niemczura, A. Noels, 2004, A&A, 415, 241-249.

Asteroseismology of the INCLUDEPICTURE "http://www.astro.ulg.ac.be/PAI/gifs/beta.gif" \* MERGEFORMATINET Cep star HD 129929. II. Seismic constraints on core overshooting, internal rotation and stellar parameters
M.-A. Dupret, A. Thoul, R. Scuflaire, C. Aerts, J. Daszynska-Daszkiewicz, P.-O. Bourge, C. Waelkens, A. Noels, 2004, A&A, 415, 251-257

The ( Scuti star XX Pyx is an ellipsoidal variable
C. Aerts, G. Handler, T. Arentoft, B. Vandenbussche, R. Medupe, C. Sterken, 2002, MNRAS 333 L35

5.2 Appeal of the IAP

- The BAG (http://www.asteroseismology.be) 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.

BAG workshops
15/10/2004: 7th BAG workshop, "Pulsations in binary and multiple stars", ORB/ROB
28/04/2004: 6th BAG workshop, "Solar-like oscillations", KU-Leuven
09/03/2004: Informal BAG meeting, KU-Leuven
19/12/2003: Informal BAG meeting, Nu Eri & HD129929, Univ. of Liège
03/10/2003: Informal BAG meeting, preparation of CoRoT Additional Programme Letters of Intent, KU-Leuven
05/09/2003: 5th BAG workshop, "Seismic modelling of ( Scuti stars", Univ. of Liège
13/06/2003: Informal BAG meeting, Asteroseismology of massive stars, KU-Leuven
13/05/2003: Informal BAG meeting, "BAG Hare and Hound exercice", KU-Leuven
28/03/2003: 4th BAG workshop, "Seismic modelling of ( Ceph stars", KU-Leuven
11/12/2001: 3rd BAG workshop, "Belgian involvement in CoRoT", Univ. of Liège
12/10/2000: 2nd BAG workshop, "Asteroseismic space missions", KU-Leuven
15/06/2000: 1st BAG workshop, "Goals and structure of the BAG", Univ. of Liège
- The example of the BAG has given rise to the creation of ENEAS (http://www.eneas.info), a similar network at European level.

- The important results published in Science and in two A&A papers constituted the topic of a documentary in the series Overleven and Matière Grise broadcasted by VRT and RTBF in 2005.

We request a guarantee to be able to continue and even intensify the existing fruitful collaboration within the BAG.

5.3 PhD and Postdoc training

- PhD defended in the framework of the BAG collaboration since 2002

- Seismic modelling of selected ( Cephei stars Mario Ausseloos - July 8, 2005
- Pulsating variables in stellar systems Lars Freyhammer- 2005
- Spectroscopic studies of selected ( Cephei stars in close binaries Katrien Uytterhoeven - September 29, 2004
- An observational study of line-profile variable B stars Maryline Briquet - March 12, 2003
- Non-radial non-adiabatic oscillations of near main sequence variable stars Marc-Antoine Dupret - December 16, 2002
- Tidal perturbations of linear, free oscillations in components of circular-orbit close binaries Tinne Reyniers - June 2002
- A spectroscopic study of the Blazhko effect in RR Lyrae Katrien Kolenberg - June 2002

- Ongoing BAG Phd studies

- Determination of fundamental parameters of OB star in the CoRoT field of view Karolien Lefever
- Classification of lightcurves from the CoRoT exoplanet field data Jonas Debosscher
- Asteroseismology of red giant stars Olga Moreira
- Asteroseismology of solar-like stars Andrea Miglio
- Rotation in ( Scuti stars and asteroseimology Gaëtane Lenain
- Photometric monitoring of open cluster Yacine Bouzid
- Asteroseismic studies of CoRoT targets Pierre-Olivier Bourge
- Spectroscopic analysis of CoRoT targets Michaël Gillon
- Scientific calibration of the CoRoT instruments Rachel Drummond

- Postdoc training
- Anwesh MazumdarKatholieke Universiteit Leuven
- Caroline BarbanKatholieke Universiteit Leuven
- Coralie Neiner
Katholieke Universiteit Leuven
- Joris De RidderKatholieke Universiteit Leuven
- Maryline BriquetKatholieke Universiteit Leuven
- Sylvie Theado
University of Liège
- Josefina MontalbanUniversity of Liège5.4 New research teams

All the Belgian asteroseismologists are already included in the BAG. It concerns about 35 people from four different Institutes. New researchers (PhD students, postdocs) in Asteroseismology are automatically enrolled in the BAG and are welcome to attend the biannual BAG Workshops.
II. Reseach Results: Stellar and Galactic Evolution (mostly ROB and KU Leuven, with a participation form Liège)

Part A : presentation from ROB

1. Stellar Evolution

Within the framework of stellar evolution our main objective is to study the final stages of evolution of intermediate mass stars, i.e. the evolution from the post-asymptotic giant branch (AGB) stage through the planetary nebula (PN) stage. This evolution is still poorly understood, mainly because of a complex interplay among various physical processes between the star and nebula. However, it makes these objects excellent laboratories of astrophysical processes.

During this first part of the IUAP we have concentrated on the study of circumstellar shells. Among other objects, we have studied in detail the very interesting multipolar post-AGB star IRAS 16594-4656. Dr. Toshiya Ueta came to the Observatory on an IUAP grant. He is specialized in the study of circumstellar shells. For the modeling of dust shells around post-AGB stars we used his 2-dimensional axisymmetric dust radiative transfer code 2-Dust (Ueta & Meixner 2003, ApJ, 586,1338). The goal is to understand the energetics of the thermal emission within the shells and the properties of dust grains. Ueta has been continuing to improve the code through (1) parallelization which reduced the execution time by 50% and (2) the inclusion of better treatments of dust grains in collaboration with R. Sczerba from Poland. The latter modification is a required step to incorporate non-equilibrium heating of very small dust grains. The 2-Dust code was used to compute a radiative transfer model of the post-AGB star HD 56126, which is one of the best-studied 21 micron proto-planetary nebulae. The results indicate that TiC nanocrystals are probably not the carrier of the 21 micron feature (Ueta et al. 2004, ApJ, 614, 371). The 2-Dust code was used by Mieke De Vlieger, graduate student at the K.U. Leuven, to construct a model for the multipolar post-AGB star IRAS 16594-4656 (Van de Steene & van Hoof ,2004, ASPC, 313, 96). Ueta was co-promotor and the modeling effort resulted in an undergraduate thesis. After additional reduction and analysis of mid-infrared images, this thesis has been reformulated for a refereed publication (Ueta et al. 2005, in preparation). To gain further insight into the shell structure of this object HST polarization images were retrieved and reanalyzed (Ueta et al. 2005, AJ, 129, 1625). From our spectroscopic near infrared observations with SOFI on the NTT we deduced that H2 is shock excited and that the spectrum also showed [Fe II] in emission, typical of shocks (Van de Steene & van Hoof, 2003, A&A, 406, 773). This B-type post-AGB star gives us the unique opportunity to study wind-nebula interaction, yet uncompromised by ionization of the circumstellar shell. We obtained the high-resolution near infrared spectra with Gemini-South to gain further insight in the winds structuring this object. Images in H2 were also retrieved from the HST archive and reduced to help to interpret the spectroscopic data. The H2 emission is spatially resolved and originates mainly at the edge of the lobes where the fast post-AGB wind impinges on previously ejected AGB material. [Fe II] comes from a different region; it is spatially unresolved and originates in shocks in the stellar wind or a circumstellar disk. There are indications that a precessing jet carved out the multipolar nebula and it became clear from our observations that this jet must be collimated.

Detecting structure developing shells would provide crucial clues to our understanding how the circumstellar shells are shaped. To investigate the critical phases of structure formation in the circumstellar shells of evolved stars, we analyzed imaging polarimetry data obtained with NICMOS polarizers on board the Hubble Space Telescope. By separating dust-scattered, linearly polarized starlight from unpolarized direct starlight we can study the optically thin circumstellar shells of post-AGB stars. This unique technique allows us to probe faint reflection nebulae around the bright central star, which can be buried under the point-spread function of the central star in conventional imaging. These images have revealed the circumstellar dust distribution in unprecedented detail via polarized intensity maps, providing a basis for understanding the three-dimensional structure of these dust shells (Ueta et al., 2005, AJ 129, 1625).

As these observations successfully revealed the 3-dimensional structure of the circumstellar shells of post-AGB stars (especially optically thin shells), observing proposals using NACO/VLT and TIMMI2/ESO3.6 have been submitted and accepted. A total of 4 nights of observing time was obtained. Near-IR coronographic imaging polarimetry with NACO has been performed in December 2004, while mid-IR imaging with TIMMI2 was performed in January 2005. For the NACO observations we selected objects which are likely developing the axisymmetric structure for the first time in their mass loss history. Coronographic imaging polarimetry with NACO allows (1) high spatial resolution probing of circumstellar environment with significantly reduced PSF effects and (2) separation of dust-scattered light off the shell (polarized component) from the direct star light (unpolarized component). The observations with TIMMI2 are in collaboration with Hans Van Winckel (K.U.Leuven). The objective is to understand how circumstellar shells of evolved stars assume the axisymmetric structure during the late AGB phase by directly probing the dust distribution via thermal mid-IR data. Well-resolved mid-IR images show structures that provide direct clues to trace the mass loss history during the late AGB Phase. Even marginally resolved images yield an upper limit for the dust-shell inner radius, which is critical for constraining dust radiative transfer models.

Griet Van de Steene (ROB) was co-promotor for the research project of Thomas Vielvoye, a master student at the K.U.Leuven. He determined the spectral types and estimated the stellar temperature of a sample of post-AGB for which we had obtained echelle spectra. Objects which are in common were identified. As Ueta had left the Observatory mid 2004, Dr. Peter van Hoof came to the Observatory on an IUAP grant in the beginning of 2005. In close collaboration with Hans Van Winckel (K.U. Leuven) Peter van Hoof will concentrate on the spectroscopic analysis and determine the surface chemical abundances of these post-AGB stars.

2. Galactic Evolution

Planetary Nebulae (PNe) are bright emission line objects, observable out to very large distances. Several PNe in many other galaxies have been detected. They are excellent probes of the chemical enrichment history of a galaxy. In collaboration with Herwig Dejonghe and an undergraduate student Christophe Praet, we analysed [O III], H± and continuum images of the Sculptor Group spiral galaxy NGC 55 obtained with the WFI instrument at the 2.2-m telescope of ESO. We identified 21 new planetary nebula candidates. We constructed the [O III]»5007ú Planetary Nebula Luminosity Function (PNLF) and determined a most likely distance of 2.30 ± 0.35 Mpc. The
distance to NGC 55 is a bit larger than previously determined distances, which means that the Sculptor group is further away from the Local Group than previously thought. The PNLF distance to NGC 55 is comparable to the PNLF distance of NGC 300 Soffner et al. (1996), adding support to the suggestion that these galaxies form a bound pair. There doesn't seem to be a shortage of planetary nebula candidates in this metal poor galaxy (Van de Steene et al., 2005, submitted)

Networking

A joint observing proposal (ROB - KULeuven) has been submitted to ESO
Toshiya Ueta (ROB) was co-promotor of the undergraduate thesis of Mieke De Vlieger (K.U.Leuven) and Griet Van de Steene (ROB) of the master research project of Thomas Vielvoye (K.U.Leuven)
Seminars about this research were given at the ROB and at K.U.Leuven

The added value of the collaboration between the various partners of the network in the context of post-AGB star research is the exchange of expertise and data to expand the research, and improved national and international contacts.

Position of the IAP Network

There are several issues related to post-AGB star research which ROB and KULeuven have started to be addressed jointly in the framework of the IUAP network, but there are still a lot of open questions that need to be solved over the next decade.

- The rate at which the central star heats up after it has left the AGB is intimately linked with the mass loss rate of the star. The mass loss causes the envelope to shrink, while the luminosity of the star remains constant, which implies that the effective temperature at the surface has to rise. Given the large uncertainties in the mass loss processes, the rate at which the central star heats up is equally uncertain. Theory is currently at an impasse and observations of a broad range of post-AGB stars are needed to deepen our understanding and constrain future theories. The same is true for the study of the chemical enrichment. Chemical enrichment occurs during the AGB phase, when the star undergoes thermal pulses. One of the most important results of these dredge-ups is that material from the interior, that has undergone thermonuclear processing, is mixed to the surface of the star where it can be observed. This gives us a unique opportunity to observe the end products of these reactions and thereby test models of the stellar interior (Van Winckel 2003). The most dramatic change in the surface composition will be for so-called s-process elements which are formed by slow neutron capture onto iron-group elements. In order to test the predictions from stellar evolution models, it is necessary to obtain a statistically viable sample of reliable abundance determinations of post-AGB stars. Currently no unified model for chemical enrichment exists (Van Winckel 2003) and a broad range of observational data on a variety of post-AGB stars are needed to test and develop theoretical models.

In close collaboration with KU Leuven Peter van Hoof (ROB) will determine surface chemical abundances of some post-AGB stars. Next, we will further analyse the hotter objects which clearly show a P-Cygni type H± profile typical of heavy mass loss, with the stellar atmosphere code Phoenix in an international collaboration. This is a state-of-the-art code capable of calculating spherically symmetric, wind-blanketed models in non local thermodynamic equilibrium (NLTE) described in Aufdenberg et al. (2002). Darko Jevremovic (University of Oklahoma) agreed to collaborate on this project by producing the Phoenix models. Jason Aufdenberg (National Optical Astronomy Observatory) agreed to act as an adviser; he is the main author of the wind module in Phoenix. Darko Jevremovic will iteratively refine the models until adequate fits to all stellar absorption and emission lines are obtained. In order to do this, it will be necessary to vary the abundances of each of the elements that are observed in the spectrum. Hence we will obtain a more accurate abundance analysis for each of these objects as well as the wind and mass loss parameters.

- What has been the mass loss history of post-AGB stars on the AGB ? Much insight into this issue can be gained from observations of nebulae around post-AGB stars and PNe with ESAs forthcoming Herschel far-IR satellite and with the ALMA sub-mm array. In both cases, a strong collaboration between the various actors of the IUAP network will place us in a strong position to apply successfully for observing time on these new facilities.

- What is the main mechanism of the shaping of post-AGB stars: binaries with disks and/or magnetic fields ? To answer this question we need to probe further the inner regions close to the star. To this end we will need the very high spatial resolution provided by interferometric measurements with VLTI.

Part B : presentation from KU Leuven

Research results

The research of the teams involved in the network concerns stellar evolution in its early and late stages. The tools used, with complementary expertise of the different partners, are optical and infrared spectroscopy, as well as the emerging opportunities of high-angular-resolution observations. The main synergies identified in the project concerned the study of late stages of stellar evolution, with their impact on the understanding on globular clusters (Liege) and on circumstellar media (Leuven and KSB/ORB). The link with the study of young stars goes through the similar diagnostic tools for studying their circumstellar environment.

In the field of young and main-sequence stars, the research carried out in the framework of this IAP culminated in the PhD thesis A study of the occurrence and time evolution of circumstellar debris disks and their relation with planetary systems by G. Decin (2003). The observational starting point of this research was constituted by several ISOPHOT programmes, the data analysis of which was a painful exercise, which benefited from the coordinated efforts with colleagues from KSB/ORB. An important result was that the timescale on which the so-called Vega phenomenon (the occurrence of debris disks around main-sequence stars) is substantially longer that was derived from earlier results, which mostly were based on data in clusters in which it is hard to discriminate genuine debris disks from the remnant disks of the star formation process. The longer timescale has now been confirmed by extensive observational programmes with NASAs Spitzer infrared satellite, and G. Decins results have been widely discussed in this context. The part of the programme devoted to K giants with infrared excesses has shown that most such objects identified as evolved debris-disk objects are in fact normal giants projected on galactic cirrus clouds, but that at least one genuine debris-disk K giant exists, in agreement with the timescale of the phenomenon as derived from main-sequence stars. Finally, a photospheric study of debris-disk stars has shown that contrary to typical planet-harbouring objects debris-disk stars are not particularly metal-rich.

In the field of galactic evolution, a new research project involving a PhD student (E. Vanhollebeke) engaged on the project was set up in late 2003. For the theoretical part in this work, a galaxy model is used which generates from a set of input parameters a set of stars for a given sky position. At the moment, this model is only calibrated for the galactic disk and halo; the goal is to restrain the possibilities for the input parameters on the Galactic Bulge (GB), so that its formation history becomes more transparent. To achieve this goal, we compare the output of the model with observations of fields in the GB (OGLE-II and 2MASS data. The observational part consists of the analysis of the near-IR spectra for OH/IR stars in the Galactic Center region. This analysis indicates that the variable amount of water and dust in these stars has a large impact on the observed CaI and NaI lines. For the highest mass-loss rates (10^-4 Msun/yr) the dust has the same effect on the CaI lines as water. The determination of the equivalent line widths of these stars is therefore not possible and no metallicity determinations based on these lines can be done. Together with the observations of the OH/IR stars, many M giants of the Galactic Center region were observed. We are currently reducing the data for these M giants with the goal to obtain their metallicity. The metallicity of the M giants is a crucial parameter for the models mentioned above, and hence its knowledge is useful in order to derive the star formation history in this part of our Galaxy. This research is part of the extensive study of stellar populations in the inner Milky Way which originated from the ISOGAL survey.

In the framework of the study of the late evolutionary stages of low- and intermediate-type stars from spectra diagnostics, one focus of our group remained on post-AGB stars, as outlined in the project description. This research was carried out by researchers financed in the framework of other programmes. Some highlights were the detection of discrete mass-loss episodes from the Red Rectangle from HST images, the confirmation that all post-AGB stars with near-infrared excesses are binaries, the identification of the putative Li-line in post-AGB stars as a Cesium line, and the detection of heavy s-process elements in low-mass post-AGB stars. A homogeneous comparison with the results of these objects reveals that the relation between the third dredge-up efficiency and the neutron nucleosynthesis efficiency found for the 21 mum objects, is further strengthened. On the other hand, a detailed comparison with the predictions of the latest AGB models indicates that the observed spread in nucleosynthesis efficiency is certainly intrinsic, and proves that different 13C pockets are needed for stars with comparable mass and metallicity to explain their abundances.

Preparation of the Herschel Central Programme

Thanks to a substantial investment in hardware and software development, Belgium has access to 20% of the guaranteed time with the PACS instrument for the Herschel Observatory mission. This programme is coordinated in Leuven, where the PACS co-PI resides. The IAP has served as the nucleus of a science team which aims at preparing the optimal scientific return from this guaranteed time.

A major fraction of the guaranteed time is devoted to a global mass loss key programme, in which besides the IAP partners K.U.Leuven, ULg and KSB/ROB also ULB takes part. The science will address the circumstellar environments of both high-mass and low-mass stars, with emphasis on spatial and spectral diagnostics of mass-loss processes in a variety of objects, with the final aim to obtain a detailed picture of the causes and evolutionary consequences of outflows during the late stages of stellar evolution. Spectral diagnostics concern both dust and gas. For the latter, coordination is now under way with the HIFI team, where we rely on the expertise of L. Decin and S. Hony, who was recently integrated in the team as a IAP post-doctoral researcher.

A second Herschel guaranteed-time key project concerns debris-disk stars and their progenitors. The aim of this programme is to map the closest debris disks at the wavelengths at which their termal emission peaks, and to explore new dust diagnostics in the far infrared.

L. Decin continues her work on the modeling of the photospheres of cool giants, also with the purpose of providing accurate calibrators of ground-based (VISIR, MIDI) and spaceborne (ISO, Spitzer, Herschel, MIRI) instruments. After achieving the final calibration of the ISO-SWS spectrometer, this work has now also proven essential for the Spitzer instruments. In addition, it has shown that many cool giants have extended atmospheres, the modeling of which now proves to be an important ingredient to understand the mass-loss processes in these stars.

The three open-time Spitzer science proposals which our group introduced at the PI level (one on AGB stars in the Magellanic Clouds, one on mineralogy of circumstellar media of evolved stars, and one on binary post-AGB stars) were all successful, and their results are presently being analysed.

Networking and position of the IAP

As a medium-sized institute involved in a variety of scientific research projects, networking is for us a necessary condition for success. In the framework of this workpackage the networks to which our group belongs are
the IAP project
the Herschel-PACS and HIFI consortia and their national subgroups
scientific consortia for other space projects (Spitzer, MIRI)
long-standing scientific collaborations with foreign researchers

Currently our institute is staffed by 3 full-time professors, 18 post-doctoral researchers, and 10 PhD students; among these 1 post-doctoral researcher and 1 PhD student are directly financed by the IAP network, where it should be pointed out that until 2005 only 1 PhD student was. It is therefore not appropriate to disconnect the IAP networking from the global one, but it deserves to be stressed that the large majority of our staff carry out their research in collaboration with colleagues from the other IAP institutes.

The major added value we see for this particular IAP network is the flexibility it provides with respect of engaging researchers in the fields where a need is felt. Other financial resources are often linked to a particular project or profile, and the IAP has enabled us more than once to equilibrate our research projects. In this context, the IAP programme is absolutely instrumental in saveguarding the long-term stability of a research team, without neglecting the necessary competitive environment which is needed for guaranteeing long-term quality.

Output and future prospects

At K.U.Leuven since 2002, eleven PhD theses were defended, all in subjects relevant for the IAP. One of these (Greet Decin) was employed within the project.

Besides with the current partners, several collaborations also involved the astronomy group of ULB. We would welcome this group, which with K.U.Leuven and KSB/ORB is involved in the construction of the HERMES spectrograph for the Mercator Telescope) to join the current network, certainly so for the workpackage on stellar evolution and nucleosynthesis.
III. Massive Stars and High Energy Astrophysics (Liège, ROB, KU Leuven)

Research Results
In the field of massive star research, one of our main objectives was to achieve a better understanding of the non-thermal radio emission observed from a subset of these objects. This phenomenon has been known for over twenty years, but many aspects were so far not understood. For instance, the production of a non-thermal radio emission requires the acceleration of electrons to relativistic velocities. One important question was whether this phenomenon is restricted to massive binary systems where the shock arising in the wind interaction zone provides a powerful site for particle acceleration, or whether relativistic particles can also be produced by the hydrodynamic instabilities that exist in the winds of single massive stars. Another important question was whether or not the relativistic electrons also produce a spectral signature in the X-ray or gamma-ray domain. If that were the case, it would allow an independent estimate of the magnetic field of the star, a parameter that is extremely difficult to evaluate for massive stars.
For this specific project, the hot star group of the Royal Observatory and the high-energy astrophysics group of the Liège University joined their efforts to obtain a multi wavelength observational description as well as a theoretical description of the phenomenon. Indeed, both partners have rather complementary expertises in the field of massive star research. The ROB group has expertise in radio observations as well as in theoretical modelling of stellar winds of single stars. On the other hand, the Liège group is active in optical and X-ray spectroscopy, gamma-ray observations and modelling of colliding wind systems.
On the observational side, we have investigated six non-thermal radio emitters of spectral type O using XMM-Newton X-ray spectroscopy, VLA radio observations, optical spectroscopy and INTEGRAL observations. Four of our targets were believed to be single (9 Sgr, HD168112, Cyg OB2 #8a, Cyg OB2 #9), whereas the other two are multiple systems (HD167971, Cyg OB2 #5). Our observations revealed that all stars display a rather hard (probably thermal) and often variable X-ray emission, but failed to reveal a power-law hard X-ray tail due to inverse Compton scattering of stellar UV photons. Instead, the hard X-ray component probably arises in a colliding wind interaction. In two cases (Cyg OB2 #8a and 9 Sgr) of presumably single stars, our optical monitoring revealed for the first time the spectroscopic signature of binarity. The VLA observations revealed recurrent variations of the flux level and the radio spectral index. In the case of Cyg OB2 #8a this modulation is related to the orbital period. For Cyg OB2 #9 and HD168112, the combination of our own and archival VLA data revealed a period in the radio fluxes. The radio variability therefore suggests that these stars are also binary systems seen under a low inclination (thus preventing us from seeing a Doppler shift of optical spectral lines). Finally, the analysis of the INTEGRAL data is currently going on. On the theoretical side, we have developed a model for the non-thermal radio emission from single hot stars, in terms of synchrotron radiation from relativistic electrons accelerated in wind-embedded shocks (using the results of time-dependent hydrodynamical simulations). The model has been applied to several stars of our sample and it turned out that it cannot explain the observations. This indicates that the observed non-thermal radio emission cannot be ascribed to shocks in the wind. This conclusion therefore supports the hypothesis that non-thermal emission is due to colliding stellar winds in a binary system.
All these results have been published in refereed journals (see the list of publications) and are also at the core of two PhD theses (Sven van Loo at ROB in April 2005, Michaël De Becker at ULg in November-December 2005).

Another important question in this field was the determination of the fundamental parameters of massive stars. Here, we have investigated a large number of O and WR-type binary systems. Using high resolution FEROS spectroscopy reduced with a revised version (developed at ROB) of the FEROS software package, the Liège group has established new accurate orbital solutions. Whenever possible, we have complemented these results by photometric data allowing us to derive absolute masses and radii for stars of different spectral types and evolutionary stages. For instance, this allowed us to establish the properties of a sample of stars in two very young open clusters (NGC6231 and IC1805). We also showed that WR20a consists of two WN6ha stars in a 3.7-day period binary system and having masses of about 80 MSun each, thus making WR20a the most massive early-type star with well-established masses.
In follow-up analyses of the optical and X-ray spectra of massive binaries, we have studied the wind interactions using various methods such as tomographic analyses of prominent optical emission lines and hydrodynamic simulations of the wind collision and the resulting X-ray emission. Our results concern early-type binaries over a wide range of wind and stellar parameters and contribute therefore significantly to a better description of the phenomenon
Again, these results have been published in refereed journals (see the list of publications) and some of them are also at the core of the PhD thesis of Hugues Sana (ULg, June 2005).

We also studied structure in the stellar winds of single O-type stars, both observationally and theoretically. Millimetre and radio continuum observations of ¶ Pup and µ Ori show that the material in the wind is not smoothly distributed, but is clumped. As the fluxes at different wavelengths come from different geometric regions in the wind, we were able to measure how the clumping decreases with distance in the wind. For the theoretical study of clumping, we developed a powerful method to study the hydrodynamical evolution of instability-generated structure in the outer winds of hot stars. This so-called pseudo-planar moving periodic box method allows us to follow wind structure out to very large distances. The code allows the theoretical interpretation of the observational clumping results and it was also used to provide input for the modelling of non-thermal radio emitters.

The various partners of our network have also investigated the spectroscopic and photometric variability of massive supergiants (some of them related to the Luminous Blue Variable - LBV phenomenon). This was done both in the optical (spectroscopy and photometry) and in the X-ray domain. Special attention was paid to the small group of Of?p stars that display spectacular recurrent spectral changes in the optical, but have rather normal X-ray spectra.
Recently (April 2005), the Liège and Leuven teams have started collaborating on asteroseismology of O-type stars. The star HD93521 (O9.5V) known to display non-radial pulsations was monitored simultaneously in photometry with the Mercator telescope by the KUL team and in spectroscopy at the Observatoire de Haute Provence by the Liège group. The data are being analysed and should provide unprecedented information on the properties of one of the few O-stars showing a clear signature of pulsations.

Finally, we have investigated the surroundings of massive stars, in two very different situations: at the beginning of their life and during evolved stages. In the former case, our XMM observations of very young open clusters reveal a wealth of moderately X-ray bright low-mass pre-main sequence stars. These objects allowed us to study the star formation history of these clusters and provide therefore clues on the still controversial issue of massive stars formation. It appears that low-mass stars seem to form first at a rather slow rate. The star formation activity slowly increases and culminates at the time the massive stars form. The formation of the massive objects then apparently stops the formation of the lower mass objects. Concerning the environment of more evolved massive stars, we studied a sample of high excitation nebulae in the LMC and SMC that display an extremely rare feature: nebular He II emission, deriving quantitative constraints on the far UV luminosity of the WR stars at the centre of these nebulae. The latter results were obtained in the framework of the PhD thesis work of Yaël Nazé (ULg, March 2004).

Networking
Major Joint Activities:
Many joint (Liège ROB) proposals on the XMM-Newton and INTEGRAL satellites as well as on the Very Large Array radio observatory.
Organization of the workshop on Massive stars and high-energy emission from OB associations in the framework of the JENAM 2005 in Liège (Liège and ROB).
Ronny Blomme (ROB) was appointed as a member of the thesis jury of Michaël De Becker (ULg).
Joint observing campaign on asteroseismology of HD93521 (Liège and Leuven).
The added value of the collaboration between the various partners of the network in the context of massive stars is clearly related to the multi-wavelength approach that allows an unprecedented description of many phenomena, and the possibility to combine the results of observations and theoretical models to get a deep understanding of their physics.
The coordination of these activities was mainly done by e-mail and through several meetings either dedicated (mainly between the Liège and ROB groups) or in the framework of other activities (like the FNRS contact group meetings).

Position of the IAP Network
In the framework of this IAP Network, we have been able to address several issues related to massive stars that are considered by many astronomers in the field as belonging to the top ten questions. For instance, we have contributed significantly to the understanding of the non-thermal radio emission of massive stars, to the determination of fundamental parameters of early-type stars and to formulating constraints on their formation mechanisms. Some of these results will certainly have an impact in a broader astrophysical context as the link between massive stars and gamma-ray bursts as well as the importance of Population III massive stars for the formation of super-massive black holes become more and more clear.
However, this is not the end of the story. There are still a lot of open questions that need to be solved over the next decade.
What are the distances and luminosities of massive stars? With its unprecedented sensitivity and accuracy, ESAs GAIA mission (to be launched around 2011-2012) will provide the distances of a huge number of stars in our Galaxy, including for the first time a significant number of early-type stars of all spectral types and luminosity classes. A Belgian consortium (including all current partners of the IAP) has been set up to address several specific aspects in the data handling of the massive stars.
What is the mass loss history of evolved massive stars? Much insight into this issue can be gained from observations of ejecta nebulae around WR stars with ESAs forthcoming Herschel far-IR satellite and with the ALMA sub-mm array. In both cases, a strong collaboration between the various actors of the IAP network will place us in a strong position to apply successfully for observing time on these new facilities.
What does the wind of a massive star look like? Due to their large opacity in the infrared domain, the stellar winds of the nearest Wolf-Rayet stars should be resolvable through interferometric observations with the VLTI. We plan also to use the VLTI to look for long period eccentric early-type binary systems seen under low orbital inclinations. In particular, this would be relevant for those non-thermal radio emitters for which our spectroscopic surveys failed to reveal evidence for the multiplicity. The ULg and ROB teams plan to do such observations together.
Where does the X-ray emission from single massive stars arise? High-resolution X-ray spectra of a few O-stars taken so far yield contradictory results. More data as well as hydrodynamical simulations are needed to clarify this issue. Again, the expertise of the various IAP partners is needed to achieve this goal.
We know that various types of structure can exist in the stellar wind of a single massive star: small-scale, stochastic clumping, large-scale Corotating Interaction Regions, disks, polar outflows. For any given star, however, it is not at all clear which types of structure are really present, and which dominate in any given geometrical region of the wind. Considerable observational material is already available, but a consistent theoretical interpretation of all these data is still lacking.

International Role (4.2B)
VLA/VLBA proposals with Raman K. Prinja (University College London) and Sean M. Dougherty (NRC Canada).
XMM-Newton and INTEGRAL proposals led by IAP teams in collaboration with various international partners from Europe (Brimingham, Leeds, Moscow,) and other countries (USA, Argentina,).
The IAP network allows the Belgian team to reach the critical mass, both in terms of knowledge and manpower, needed to play a leading role in these collaborations.

PhD and postdoc training
PhDs in the field of massive stars from 2001 until end of 2005: Pierre Royer (Liège, now KU Leuven), Yaël Nazé (Liège), Sven Van Loo (ROB), Hugues Sana and Michaël De Becker (Liège) (none financed by IAP).
Added value to PhDs: knowing a larger number of collaborators (made possible through the IAP) makes it easier for them to find a post-doc position.
IV. Extragalactic Astrophysics and ILMT (Liège, ROB and Leuven)

Research Results :

During the past years, the Liège (Institute of Astrophysics and Geophysics, IAGL) and the Uccle (Royal Observatory of Belgium, ROB) teams have been 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).

Moreover, the Liège (IAGL) and Leuven (KULeuven) teams are involved in COSMOGRAIL, an international collaboration also involving teams from Switzerland, the United Kingdom, Uzbekistan and India. The aim of this ambitious international project is to determine the main cosmological parameters from the photometric monitoring of a large number of multiply imaged quasars. This project involves four ground-based telescopes (including Mercator run by the KULeuven team) as well as observations obtained with the Hubble Space Telescope.

IVa. Extragalactic Astrophysics

Gravitational lensing perturbs our view of the distant Universe and affects our physical understanding of various classes of extragalactic objects. The great interest in gravitational lensing comes from the fact that this phenomenon can be used as an astrophysical and cosmological tool. Indeed, gravitational lensing may help in deriving (i) the distance scale of the Universe, via the determination of the Hubble constant H0 based upon the measurement of the time delay (t between the observed lightcurves of multiply imaged quasars, (ii) the values of other cosmological parameters ((0 and (0), (iii) the mass distribution M(r) of the lens, (iv) (0 and (0 extinction law in the deflector usually located at high redshift, (v) the nature and distribution of luminous and dark matter in the Universe, (vi) the size and structure of quasars, (vii) the size of absorbing intergalactic gas clouds and (viii) upper limits on the density of a cosmological population of massive compact objects.

One of the most promising applications of the gravitational lensing phenomenon is the determination of the main cosmological parameters H0, (0 and (0 from the measurement of the time delay between the different images of multiply imaged quasars.

The classical measurements of these cosmological parameters usually rely on the use of standard candles (i.e. light sources whose intrinsic luminosity is supposed to be known and whose distance can then be derived from a measurement of their apparent luminosity). However, these distance measurements rely on a number of assumptions and on the correction of sometimes poorly known systematic errors. The most useful standard candles are Type Ia Supernovae, which can be observed to large distances. However, the same data analyzed by different groups still lead to values which may differ by more 20%. Other measurements, based on the cosmic microwave background, have claimed very high accuracies. Unfortunately, they cannot alone provide an independent measurement of H0 or other parameters, and need some input from other techniques.

In view of these uncertainties and possible systematic errors, it appears desirable to have a completely independent determination of H0 and, if possible, the other cosmological parameters. Gravitationally lensed quasars provide such an independent method, through the measurement of the time delay between different images of the same quasar.

Up to now, the time delays have been determined in about ten gravitationally lensed quasars, four of them by our group in the framework of the PhD thesis of Ingunn Burud. The derived values of H0 are on average about 20% lower than the most generally accepted value. However, the error bars are still too large to draw any firm conclusion.

The time delay method has its own uncertainties and systematic errors, but they are of a completely different origin from those of the classical methods and can be reduced in two ways.

First, the time delays should be known with better accuracy. This accuracy improvement can be realized through the regular monitoring of a significant number of targets with telescopes of good optical and photometric quality. This is why we have set up the COSMOGRAIL collaboration (COSmological Monitoring of GRAvItational Lenses, Web page: http://www.cosmograil.org).

The observations are regularly carried out at three telescopes: the 1.2m Swiss Euler telescope at La Silla (Chile), the 1.2m Mercator telescope from KULeuven at La Palma (Canary Islands) and the 1.5m telescope at Maidanak Observatory (Uzbekistan). Observations are also scheduled at the 2m Robotic Telecope of the Liverpool University (also at La Palma). The COSMOGRAIL program on the Mercator telescope is embedded in the science plan of the Mercator telescope which ensures the detailed monitoring of the systems the whole year through. A detailed web-log was developed to ensure good coordination of the different sites. Members of the COSMOGRAIL consortium include from the IUAP institutes: L. Le Guillou, H. Van Winckel and C. Waelkens (Leuven), P. Magain and S. Sohy (Liège).

The aim of the project is to measure the time delays in at least 20 gravitational lens systems with 2 to 3% accuracy. For the northern hemisphere, 15 lenses are being monitored with Mercator with measurements 2-3 times a week of all observable systems. The whole COSMOGRAIL sample presently contains 22 sources.

In order to improve the determination of H0, the models of the lensing galaxies should also be improved. This can be done through several ways. First, the geometry of the system should be known with the best possible accuracy. We are presently measuring the missing lensing galaxy redshifts on the basis of VLT spectra. The positions of the quasar images and of the lensing galaxy/galaxies are also measured from a careful processing of the HST images, which are available for all the systems. The images are deconvolved through the use of our MCS algorithm. This allows not only to improve the accuracy of the measurement of the image positions, but also to detect fainter components, such as arcs or Einstein rings, which are very useful for constraining the mass distribution in the systems (see the figure below).

HST image of the gravitational lens H1413+117 (left) and its improvement by the MCS algorithm (right). The lensing galaxy and arc structures are completely masked by the complicated Point Spread Function of the HST on the original image (left) and can only be detected after deconvolution (right).

Once the Hubble constant will be known with sufficient accuracy, the gravitational lens systems will become extremely powerful tools for the study of the dark matter distribution in the lensing galaxies.

Due to the arcsec scale (or less) of the angular separation between the multiple images of lensed QSOs, the Hubble Space Telescope (HST) is badly needed to confirm the nature of the lens candidates, usually first identified by means of ground-based observations. This is well illustrated for the case of the quadruply imaged quasar 1RXS J1131-1231 that has been discovered by our team and extensively studied with HST (see the picture below). This system is composed of four macro-lensed images of a quasar surrounded by an optical Chwolson-Einstein ring. Observations of this interesting target have also been carried out with the ESO Very Large Telescope (VLT), with the Very Large Array (VLA) and with the Chandra X-ray Observatory. The redshift of the lensed quasar is z=0.65, corresponding to a very near cosmic mirage.
Collaborative work on this exciting target is taking place between IAGL, ROB, ESO, CFHT, University of Kiev, Imperial College of Science Technology and Medicine, University of Hawaii.

Composite HST color image of the new gravitational lens system RXS J1131-1231

Multiply imaged QSOs provide general constraints on the mass distribution of the lensing galaxies. For example, if the value of the Hubble constant H0 and the lens and source redshifts are known, the total mass can be derived from the angular separation between the lensed QSO images. This is the simplest and most direct astrophysical application of gravitational lensing. If a time delay is also measured, the lensing mass can be obtained independently of the cosmological parameters H0, (0, (0 and the source redshift. The Hubble Space Telescope plays a crucial role in detecting the main lenses, which are faint, extended, high redshift objects located between bright and angularly close (~1 arcsec) images of the background quasars. Careful subtraction of the HST Point Spread Function and/or deconvolution is often mandatory. Based upon direct imagery with the ACS camera onboard HST, it was easy to detect the lens galaxy for the quadruply imaged quasar 1RXS J1131-1231 A-D (see the image, above).

Our teams have also participated to the photometric monitoring and the lightcurve analysis of several multiply imaged quasars among which the Einstein Cross 2237+0305 and UM673. The data of UM673 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 have allowed to detect microlensing signatures on the light-curve of the bright component. Several independent methods (MCS, General and image subtraction) for the analysis of the direct CCD images have been used.

Nakos et al. (Uccle) have 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.

Multiply imaged quasars also deserve very special investigations to determine the extinction law in the lensing galaxies. Indeed, when the lines-of-sight corresponding to the different images probe different dust optical depths in the lens, a differential reddening is observed between the lensed images. Until now, only Galactic parametric curves have been fitted from photometric data but high quality spectrophotometry should allow to directly determine the extinction law at high redshift and compare it with that observed in the Milky Way, in the Magellanic Clouds and in a few local galaxies. Studies of the extinction law among multiply imaged quasars, in general, have been reported in the PhD thesis of Jean.

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 anti-coincidences 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 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 cosmological unlikeness of these quasar pairs are irrelevant.

An efficient algorithm to deconvolve the spectra of very nearby quasars has been 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.

Review papers, as well as popular articles, on the subject of gravitational lensing have been published. Didactical experiments illustrating the formation of gravitational lens systems have been presented at international conferences and during seminars. Several optical lens simulators made of plexiglass have been produced by our team and used to simulate the formation of multiply imaged quasars by a foreground lens galaxy. Such didactictal experiments enable one to reproduce all image configurations (cf. double or quadruple lensed images, Einstein ring, giant luminous arcs, arclets, etc.) that have been observed with the Hubble Space Telescope. One of these simulators is being used in the 'Cosmology' exhibition organized at the National Air and Space Museum in Washington from 2000 until 2015.

A non exhaustive, although quite complete, bibliography dedicated to theoretical and observational studies of gravitational lens systems in the form of a public database (totaling more than 3000 titles) as well as a database summarizing the main observational and physical parameters of multiply imaged sources, including a set of color images of most of these cosmic mirages, are available on the web at the following URL address HYPERLINK http://vela.astro.ulg.ac.be/grav_lens/grav_lens.html http://vela.astro.ulg.ac.be/grav_lens/. This database is very frequently used by scientists from the astronomical community at large. More than 40.000 entries have been registered.

Teams from IAGL and from ROB are part of the XMM-LSS international Consortium in which astronomers from 15 different institutes are joining their efforts to produce a wide X-ray survey for studies of large scale structures (hereafter LSS) and active galactic nuclei (AGN/QSOs) at high galactic latitude in the Universe. The PI of the XMM-LSS project is Dr. M. Pierre (CEA, Saclay, France).
The XMM-LSS survey characteristics are the following : we presently (GT, AO-1 AO-3) have covered a 5 deg2 area and reached a sensitivity of at least 5 10-15 erg. cm-2.s-1 for point-like sources and 10-14 erg.cm-2.s-1 for typical cluster emission in the [0.5-2] keV band. Our goal is to cover a total area of 10 deg2. The XMM-LSS survey mainly consists of 10 ks XMM/EPIC pointings separated by 20 arcmin offsets. The survey area surrounds two deep XMM surveys based on guaranteed time: the XMM_SSC/Subaru Deep Survey (80 ks exposures in 1 deg2) and the XMM Medium Deep Survey (XMDS; 20 ks exposures in 2 deg2) also corresponding to the VIRMOS-DESCART Deep Survey [deep], the latter being a collaboration between several instrumental teams: XMM-OM (Liège), XMM-EPIC (IASF-MILANO), XMM-SSC (Saclay), CFHTLS (Saclay, IAP) and VIRMOS (LAM, IASF-MILANO, OAB). This area is also being observed by the associated DESCART-VIRMOS Deep Survey [wide], the Spitzer Wide Area Infrared Extragalactic (SWIRE) SIRTF Legacy Survey, the Galex ultraviolet survey and the NOAO deep survey; the 8.75 deg2 UKIDSS survey is centered on the Subaru Deep Survey and the CTIO R-z' imaging covers a region corresponding to the VVDS [wide] and [deep] surveys. A very detailed description of the XMM-LSS project and consortium activities are accessible via the URL HYPERLINK "http://vela.astro.ulg.ac.be/themes/spatial/xmm/LSS/" http://vela.astro.ulg.ac.be/themes/spatial/xmm/LSS/. This web page is maintained and entirely managed by the Liège team.

Assuming the current favoured cosmological values for INCLUDEPICTURE "http://vela.astro.ulg.ac.be/images/math/Lambda.gif" \* MERGEFORMATINET CDM, the entire cluster/group population will be detected out to z = 0.5 and the total number of clusters will be of the order of 150 with 0 < z < 1 (about half of them below z < 0.7). The XMM-LSS survey will also be ideal to probe the behaviour of the bright end of the X-ray luminosity function beyond z > 1 : a new exciting territory.
At the low X-ray flux achieved by the XMM-LSS survey, there are approximately 300 X-ray sources per square degree, among which typically : 15-20 are galaxy clusters, about 200 AGN and QSOs (100 QSOs/AGN with z < 1) and the remainder stars and nearby galaxies. The surface density of QSOs/AGN in our proposed survey is almost an order of magnitude larger than those expected in the on-going (colour biased, z < 2.5, ) optical surveys carried out over large sky areas (SDSS, 2dF, etc.). Compared to optical surveys, the completeness of X-ray selected QSOs/AGN is also known to be much better defined.
The high sensitivity and good point-spread function of XMM has opened a new era for X-ray LSS studies. Some 1000 times more sensitive than the REFLEX survey - the largest cluster survey over a single area to date - the XMM-LSS survey has been designed to probe the large scale distribution of galaxy clusters out to z ~ 1 and of QSOs much further out. This will provide unprecedented insights onto LSS formation and, thus, cosmology. We will be able to probe the nature and amount of dark matter, the initial fluctuation spectrum and other fundamental cosmological parameters.

The primary science goals of the entire XMM-LSS survey are to :
- Map the LSS as outlined by galaxy clusters and groups out to z = 1. This will reveal the topology of the spatial distribution of deep potential wells at truly cosmological distances.
- Compute the correlation function of clusters of galaxies in two redshift bins 0 < z < 0.5, 0.5 LCGM¯M-RÖT¨Z±]Å]#_õÿp#
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