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  1. Multiplicity among embedded protostars Gaspard Duchêne (Grenoble) J. Bouvier, S. Bontemps, P. André, F. Motte, A. Djupvik, A. Ghez Multiplicity in Star Formation - Toronto - 16-18 May 2007

  2. General background • Multiplicity well studied for ages  106 yrs Large excess in some young populations Scaled MF from VB surveys Apparent dependence on environment T Tauri stars open clusters field Multiplicity in Star Formation - Toronto - 16-18 May 2007

  3. General background • Interpretation still ambiguous: Scaled MF from VB surveys ? Multiplicity in Star Formation - Toronto - 16-18 May 2007

  4. General background • Interpretation still ambiguous: Tracer of different initial states ? Scaled MF from VB surveys  Physics of core fragmentation Higher cloud mass Multiplicity in Star Formation - Toronto - 16-18 May 2007

  5. General background • Interpretation still ambiguous: Tracer of different initial states ? Scaled MF from VB surveys  Physics of core fragmentation Denser clusters Tracer of a different early evolution ? Stellar dynamics Multiplicity in Star Formation - Toronto - 16-18 May 2007

  6. General background • Need to survey even younger systems: • Embedded protostars ! Class 0 age ~ 104 yrs, radio Scaled MF from VB surveys ? Class I age ~ 105 yrs, IR Reipurth (2000) 80-85% MF Multiplicity in Star Formation - Toronto - 16-18 May 2007

  7. This work : basic presentation • Objective: survey of protostars with deep, high resolution, NIR imaging • Several SFRs • Taurus vs. Orion • Focus on • Class I • Flat Spectrum (FS) FS Class I Kaas et al. (2004) Multiplicity in Star Formation - Toronto - 16-18 May 2007

  8. This work : basic presentation • Observations: • Seeing-limited: CFHT-IR (0.6”) JHK • Diffraction-limited: VLT-NACO (0.07”) HKL’ CFHT-IR VLT-NACO ~7 mag ~7 mag 1’’ 10’’ 0.1’’ 1’’ 10’’ Duchene et al. (2007) Duchene et al. (2004) Multiplicity in Star Formation - Toronto - 16-18 May 2007

  9. Additional sample • When available, we also added older HST/NICMOS images to our survey • Somewhat poorer resolution (0.15’’) • Higher PSF stability • Higher sensitivity (fainter targets) 0.24’’ Padgett et al. (1999) Multiplicity in Star Formation - Toronto - 16-18 May 2007

  10. This work : sample • Overview of our sample: Multiplicity in Star Formation - Toronto - 16-18 May 2007

  11. This work : sample • Sample represents ~40% of all known Class Is and FSs in each cloud • Magnitude bias • Population distributed in all clouds • Not densely clustered (except in Serpens) • Serpens and Orion: higher luminosities Multiplicity in Star Formation - Toronto - 16-18 May 2007

  12. New tight systems IRAS 04361+2547 ? VLT-NACO Ks HST-NICMOS H Terebey et al. (1998) 0.31’’ Duchene et al. (2007) Multiplicity in Star Formation - Toronto - 16-18 May 2007

  13. Results : multiplicity rates • 110-1400 AU: 27 +/- 6 % (Tau+Oph) • 14-1400 AU: 45 +/- 8 % (Tau+Oph) • 45-1400 AU: 30 +/- 6 % (all clouds) • consistent with Reipurth et al. (2004) • Factor ~1.5 excess over field stars • No cloud-to-cloud difference • First evidence for high early MF in Orion ! Multiplicity in Star Formation - Toronto - 16-18 May 2007

  14. Results : multiplicity rates • Dependence on evolutionary stage? NO! • Class I vs. FS sources: • No significant difference • Objects with extended envelope: • Supposedly younger than other ClassI objects • Seeing-limited observations suggested a trend… • … but diffraction-limited observations proved otherwise Multiplicity in Star Formation - Toronto - 16-18 May 2007

  15. Results : other properties • Masses unknown from luminosity and IR fluxes • Need HR spectroscopy for mass ratios • High-order multiples: 5 triples overall • Not more than found among T Tauri stars or, probably, field stars • No unstable multiple system • Already destroyed or never existed Multiplicity in Star Formation - Toronto - 16-18 May 2007

  16. Results: other properties • Same MF in all clouds but differences in the distribution of separations Orion is different from other clouds at the 2.7  level (99.3%) Taurus All Orion companions Needs confirmation with larger samples Ophiuchus Duchene et al. (2007) Multiplicity in Star Formation - Toronto - 16-18 May 2007

  17. Overview and implications • High multiplicity rate of Class I and FS sources in all clouds • Even in the Orion molecular cloud ! • No many-star systems left by ~105 yrs • Consistent with quasi-universal scenario • Small-scale physics dominates fragmentation and/or early dynamical evolution Multiplicity in Star Formation - Toronto - 16-18 May 2007