Michaël De Becker (Groupe d'AstroPhysique des Hautes Energies)

1. ARC Meeting, Colonster Long baseline interferometry applied to the study of massive stars: current observations and prospects for VSI Michaël De Becker (Groupe d'AstroPhysique des Hautes Energies)

2. ARC Meeting, Colonster Science topics related to massive stars likely to benefit from high angular resolution imaging Observations with current facilities Prospects for observations with next generation instruments : VLTI-Spectro-Imager (VSI) Concluding remarks Outline

3. ARC Meeting, Colonster Angular resolution ~ mas (for baselines of ~ 100 m in the near IR) But: O-type and WR-type stars are typically at distances of a few kpc → stellar diameters ~ a fraction of mas Science topics

4. ARC Meeting, Colonster Science topics Angular resolution ~ mas (for baselines of ~ 100 m in the near IR) But: O-type and WR-type stars are typically at distances of a few kpc → stellar diameters ~ a fraction of mas IR radiation ~ density tracer of stellar winds (continuum and emission lines) But: quick decrease of the wind density with radial distance → increasing intensity contrast

5. ARC Meeting, Colonster Science topics Angular resolution ~ mas (for baselines of ~ 100 m in the near IR) But: O-type and WR-type stars are typically at distances of a few kpc → stellar diameters ~ a fraction of mas IR radiation ~ density tracer of stellar winds (continuum and emission lines) But: quick decrease of the wind density with radial distance → increasing intensity contrast → investigating individual massive stars or their stellar winds is not easy with present interferometric facilities

6. ARC Meeting, Colonster Science topics What about multiple systems? 1 AU at 1 kpc → angular separation of 1 mas

7. ARC Meeting, Colonster Science topics What about multiple systems? 1 AU at 1 kpc → angular separation of 1 mas Ang. res.: a few mas Lin. sep.: a few AU Orb. period: a few years ↓ ↓

8. ARC Meeting, Colonster Science topics What about multiple systems? 1 AU at 1 kpc → angular separation of 1 mas Typically, current long baseline interferometric facilities with instruments working in the infrared domain could resolve binary systems with periods of at least a few years, provided they are located at distances of the order of a few kpc. However, other factors should be considered such as the inclination, or the eccentricity of the system.

9. ARC Meeting, Colonster Science topics What can we envisage in this context? • Multiplicity studies of massive stars: Interferometry is a complementary technique w.r.t. usual spectroscopic techniques (see e.g. low inclination angle of the orbital plane... )

10. ARC Meeting, Colonster Science topics What can we envisage in this context? • Multiplicity studies of massive stars: Interferometry is a complementary technique w.r.t. usual spectroscopic techniques (see e.g. low inclination angle of the orbital plane... ) • Nothing else?... Investigate wind-wind interaction regions in colliding-wind binaries, and related physical processes... « We have never really seen such an interaction region! »

11. ARC Meeting, Colonster Science topics What can we envisage in this context? • Multiplicity studies of massive stars: Interferometry is a complementary technique w.r.t. usual spectroscopic techniques (see e.g. low inclination angle of the orbital plane... ) • Nothing else?... Investigate wind-wind interaction regions in colliding-wind binaries, and related physical processes... « We have never really seen such an interaction region! »

12. ARC Meeting, Colonster Science topics What can we envisage in this context? • Multiplicity studies of massive stars: Interferometry is a complementary technique w.r.t. usual spectroscopic techniques (see e.g. low inclination angle of the orbital plane... ) • Nothing else?... Investigate wind-wind interaction regions in colliding-wind binaries, and related physical processes... « We have never really seen such an interaction region! »

13. ARC Meeting, Colonster Current observations • Observation campaigns led by the GAPHE: « Interferometric observations of the triple system and non-thermal radio emitter HD167971 » (in collaboration with AEOS) - massive triple system - VLTI : 3 UTs and AMBER - 2 observations executed with a time interval of about 3 months - orbital elements are needed to investigate processes related to colliding-winds: i.e. particle acceleration and non-thermal emission processes

14. ARC Meeting, Colonster Current observations • Observation campaigns led by the GAPHE: «Multiplicity investigation of two Wolf-Rayet stars with VISA  » • Project accepted in the context of the Belgian Guaranteed Time on VISA (observing run in July 2009) • Instrumentation used : 3 ATs with AMBER • First objectives: resolve the systems, and then determine the orbital elements • Targets : WR106 and WR112 (both WC-type) • Physics investigated later on: - WR112 in a non-thermal emitter (part. acceleration...) - WR stars known to be dust makers : the colliding-wind region of WC-type stars is known to constitute an efficient nucleation site for dust particles

15. ARC Meeting, Colonster Prospects for VSI • VLTI-Spectro-Imager (VSI) : second generation instrument designed to combine) 6 beams (first light in 2015?) → many baselines observed simultaneously → image reconstruction possible!! (see Olivier Absil's talk) • In the context of the actitivites of the Science Group of the VSI consortium, science topics related to massive stars have been explored • A list of Wolf-Rayet stars is included in the target list of the main scientific programme of the instrument

16. ARC Meeting, Colonster Prospects for VSI Example of image reconstruction: dust making WR star Synthetic images of dust making WR stars and associated reconstructed images assuming 6 beams, for 2 different inclinations of the system (0 or 60 degrees) • VSI is expected to improve considerably our view of such systems, and to discover other « pinwheel » nebulae close to WR binaries • Such observations will improve our understanding of the physics of dust production is these environments

17. ARC Meeting, Colonster Concluding remarks • Considering the capabilities of present interferometric facilities, science topics related to the study of massive stars have clearly been identified • Observation campaigns have been initiated by the GAPHE to study massive binaries (O and WR-type) with the VLTI (collaborations with AEOS) • Next generation instruments such as VSI are very promising notably for studies related to massive stars. Science topics related to such targets are included in the main science programme prepared by the Science Group of the VSI consortium

18. ARC Meeting, Colonster Concluding remarks • Our group is taking part to an international effort to initiate a dialogue between the « interferometric community » and the « massive star community » The Interferometric View on Hot Stars, Vina del Mar, Chile (ESO conference), 2-6 March 2009 Massive Stars Meeting, Fourth CHARA meeting, Nice, France, 19-20 March 2009