04/03/2011ARC Meeting, CSL Long baseline interferometry applied to the study of colliding-wind massive binaries: current status and prospects for the near future Michaël De Becker (Groupe d'AstroPhysique des Hautes Energies)

04/03/2011ARC Meeting, CSL Outline Why is long baseline interferometry interesting for us? Why are colliding-wind binaries important in stellar astrophysics? Observations with current facilities Concluding remarks

04/03/2011ARC Meeting, CSL Why long baseline interferometry? 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

04/03/2011ARC Meeting, CSL Why long baseline interferometry? 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 Not yet very performant for the study of individual O and WR stars.

04/03/2011ARC Meeting, CSL Why long baseline interferometry? What about multiple systems? 1 AU at 1 kpc → angular separation of 1 mas

04/03/2011ARC Meeting, CSL Why long baseline interferometry? 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 ↓ ↓

04/03/2011ARC Meeting, CSL Why long baseline interferometry? 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.

04/03/2011ARC Meeting, CSL Why long baseline interferometry? So far, massive binaries have been identified using 1. Spectroscopy : generally for short separations (up to a few AU), biased due to the inclination of the orbit w.r.t the line of sight 2. Speckle : larger separations (from a few 10 AU up to ~ 1000 AU) 3. AO assisted imaging : much larger separations (more than a few 100 AU) Multiplicity investigations of massive stars are very important, but this is not an easy task !

04/03/2011ARC Meeting, CSL Why long baseline interferometry? Multiplicity investigations of massive stars are very important, but this is not an easy task ! Long baseline interferometry fills a gap in the exploration of binary systems, as it is likely to detect companions with separations of the order of a few AU up to several tens of AU. Interferometry is therefore a complementary tool with respect to other techniques!

04/03/2011ARC Meeting, CSL Why long baseline interferometry? Multiplicity investigations of massive stars are very important, but this is not an easy task ! Long baseline interferometry fills a gap in the exploration of binary systems, as it is likely to detect companions with separations of the order of a few AU up to several tens of AU. Interferometry is therefore a complementary tool with respect to other techniques! Complementarity in the orbital parameter space investigated Complementarity of the information obtained through different techniques (spectroscopy vs interferometry)

04/03/2011ARC Meeting, CSL Why colliding-wind massive binaries?

04/03/2011ARC Meeting, CSL Why colliding-wind massive binaries? Thermal X-ray emission Post-shock plasma temperature up to several 10 MK, with significant phase-locked variations (Stevens et al. 1992, ApJ, 386, 265; Pittard & Stevens 1997, MNRAS, 292, 298)

04/03/2011ARC Meeting, CSL Why colliding-wind massive binaries? Thermal X-ray emission Post-shock plasma temperature up to several 10 MK, with significant phase-locked variations (Stevens et al. 1992, ApJ, 386, 265; Pittard & Stevens 1997, MNRAS, 292, 298) Particle acceleration Synchrotron radiation detected in the radio domain; potential non-thermal radiation investigated in X-rays and gamma-rays in order to study the particle acceleration process in CWB (Pittard & Dougherty 2006, MNRAS, 372, 801; De Becker 2007, A&ARv, 14, 171)

04/03/2011ARC Meeting, CSL Why colliding-wind massive binaries? Thermal X-ray emission Post-shock plasma temperature up to several 10 MK, with significant phase-locked variations (Stevens et al. 1992, ApJ, 386, 265; Pittard & Stevens 1997, MNRAS, 292, 298) Particle acceleration Synchrotron radiation detected in the radio domain; potential non-thermal radiation investigated in X-rays and gamma-rays in order to study the particle acceleration process in CWB (Pittard & Dougherty 2006, MNRAS, 372, 801; De Becker 2007, A&ARv, 14, 171) Dust production In the case of WC-type WR binaries, the wind-wind interaction region can act as a nucleation site for dust particles (Williams et al. 1985, MNRAS, 215, 23; Williams et al. 1994, MNRAS, 266, 247)

04/03/2011ARC Meeting, CSL Observations Observation campaigns: « Interferometric observations of the triple system and non-thermal radio emitter HD » (in collaboration with AEOS) - massive triple system - VLTI : 3 UTs and AMBER - 2 observations executed with a time interval of about 2 months - orbital elements are needed to investigate processes related to colliding-winds: i.e. particle acceleration and non-thermal emission processes

04/03/2011ARC Meeting, CSL Observations Observation campaigns: « Interferometric observations of the triple system and non-thermal radio emitter HD » (in collaboration with AEOS) The system is resolved by the VLTI at two epochs separated by ~ 2 months The flux ratio is determined (~ 0.80) The relative position of the stars changed slightly, but significantly, during this short time interval, suggesting a quite eccentric orbit. A monitoring is necessary to derive orbital elements.

04/03/2011ARC Meeting, CSL Observations Observation campaigns: «Absolute mass determination of high mass stars » - Project in collaboration between Grenoble, Amsterdam and Liège in progress at ESO - Instruments : AMBER, PIONIER, spectroscopy... - Targets : massive binaries (O-type)... and binary candidates - Aims : (1) determine absolute masses of stars using interferometry and spectroscopy in complementarity (2) detect companions in the case of suspected long period binaries

04/03/2011ARC Meeting, CSL Observations Observation campaigns: «Absolute mass determination of high mass stars » Important results in the context of the physics of CWBs : - resolution of a companion in the case of 9 Sgr - resolution of a companion in the case of HD93250 (important in the case of CWBs accelerating particles!) - Project in collaboration between Grenoble, Amsterdam and Liège in progress at ESO - Instruments : AMBER, PIONIER, spectroscopy... - Targets : massive binaries (O-type)... and binary candidates - Aims : (1) determine absolute masses of stars using interferometry and spectroscopy in complementarity (2) detect companions in the case of suspected long period binaries

04/03/2011ARC Meeting, CSL Observations Observation campaigns: «Multiplicity investigation of a Wolf-Rayet star with VISA » - DDT approved project on VISA (observing runs in July 2011) - Instrumentation used : 3 ATs with AMBER - First objectives: resolve the systems, and then determine the orbital elements - Target : WR106 (WC-type, dense stellar wind) - Physics investigated later on: WR star known to be dust maker : the colliding-wind region of WC-type stars is known to constitute an efficient nucleation site for dust particles

04/03/2011ARC Meeting, CSL Observations Prospects for the near future: « Imaging dust producing Wolf-Rayet binaries with PIONIER » Study of the physics of dust formation in WC-type binaries, using the PIONIER instrument (combination of 4 beams, increasing the uv coverage)

04/03/2011ARC Meeting, CSL Observations Prospects for the near future: « Imaging dust producing Wolf-Rayet binaries with PIONIER » Study of the physics of dust formation in WC-type binaries, using the PIONIER instrument (combination of 4 beams, increasing the uv coverage)

04/03/2011ARC Meeting, CSL 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 to study massive binaries (O and WR-type) with the VLTI (collaborations between GAPHE and AEOS) First results are encouraging. The feasibility has clearly been demonstrated. Other projects just started, extending the collaboration to other teams (Grenoble, Amsterdam, OHP...).