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

Multiplicity in Star Formation - Toronto - 16-18 May 2007 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

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

Multiplicity in Star Formation - Toronto - 16-18 May 2007 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

Multiplicity in Star Formation - Toronto - 16-18 May 2007 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

Multiplicity in Star Formation - Toronto - 16-18 May 2007 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

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

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. (2004) Duchene et al. (2007) Multiplicity in Star Formation - Toronto - 16-18 May 2007

Multiplicity in Star Formation - Toronto - 16-18 May 2007 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

Multiplicity in Star Formation - Toronto - 16-18 May 2007 This work : sample Overview of our sample: CFHT-IR VLT-NACO Class I FS Taurus 12 10 11 5 Ophiuchus 16 25 Serpens - 2 6 Orion 4 8 Multiplicity in Star Formation - Toronto - 16-18 May 2007

Multiplicity in Star Formation - Toronto - 16-18 May 2007 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

Multiplicity in Star Formation - Toronto - 16-18 May 2007 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

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

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

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

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

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