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 May 2007

2. 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 May 2007

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

4. 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 May 2007

5. 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 May 2007

6. 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 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 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. (2004)
Duchene et al. (2007)
Multiplicity in Star Formation - Toronto May 2007

9. 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 May 2007

10. 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 May 2007

11. 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 May 2007

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

13. Results : multiplicity rates
AU: 27 +/- 6 % (Tau+Oph)
AU: 45 +/- 8 % (Tau+Oph)
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 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 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 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 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 May 2007