1. Jes Jørgensen (Leiden), Sebastien Maret (CESR,Grenoble)
Submm Survey of Low-mass Protostars: Tracing the physical and chemical structure and evolution
Jes Jørgensen (Leiden), Sebastien Maret (CESR,Grenoble)
E. van Dishoeck, E. Caux, C. Ceccarelli, F. Schöier, M.Hogerheijde, A. Tielens
Other surveys being carried out in Texas, Manchester, ….
DUSTY 2004 meeting, Paris, Oct

2. This study
Establish the physical and chemical structure of a sample of ~ 20 low-mass protostars (class 0/I); using single-dish obs. (JCMT, IRAM, Onsala), mm interferometry and detailed radiative transfer modeling.
Relation between physical and chemical properties?
Diagnostics of different protostellar components?
Can chemistry be used to trace the protostellar evolution?

3. Approach SCUBA obs. + Rad. transfer model. Dust continuum emission
CS, SO
HCO+, N2H+
HCN, HNC, CN
DCN, DCO+
H2CO, CH3OH
SO2, SiO, H2S, CH3CN (~ 16 species, 40 lines)
Dust continuum emission
Physical structure
Molecular excitation
Chemical structure
Single-dish obs. + Monte Carlo model.
Detailed chemical model
Interferometry: small scale structure

4. Physical structure from dust emission
Ice evaporation
Freeze-out
Joergensen et al. 2002

5. Outer envelope: CO freeze-out

6. Example: modeling of CO lines toward L723
- Adopt n(r) and T(r) from continuum: constrain abundances
- Overall philosophy: use simplest possible abundance models (constant, jump, drop) and add complexities only if needed (‘retrieval’ method)
- ‘Forward’ modeling also being pursued; consistent picture

7. CO depletion: constant abundance
“Canonical” CO abundance (Lacy et al. 1994)
CO freezes out at low temp. ( 35 K)
Objects with high envelope masses (younger?) show significantly higher degree of CO depletion

8. “Drop” abundance model
nde
Tev
Constant
Drop

9. - Drop abundance much better fit to J=1-0 to 3-2
L723:
Constant abundance model
“Drop” abundance model
- Drop abundance much better fit to J=1-0 to 3-2

10. Abundance
Pre-stellar core:
Low temperature
Depletion toward center
...but not edge
Protostellar core:
Central heating ~ temperature gradient
Thermal desorption toward center
...outside (low T): depletion/no depletion regions as in pre-stellar stages
Is this an evolutionary sequence?
Can chemistry constrain timescales? ~105 yr?

11. HCO+ and N2H+ abundances
Correlation HCO+ with CO
Anticorrelation N2H+ with CO
- Empirical chemical network
- Freeze-out of CO leads to
very high deuteration ratios
Jørgensen et al. 2004

12. Chemical structure confirmed by interferometry
 450 m cont.
 N2H+
 C18O
Jørgensen 2004

13. Inner envelope: Ice evaporation

14. Inner envelope chemistry
Evaporation of ices other than CO
Evaporated ices and complex organics around solar-mass star
IRAS
Hot CH3OH gas
Tex~80 K
JCMT
CH3OH data can only be fitted if abundance jumps by factor of
in inner region at T=90 K radius
Ceccarelli et al. 2000, Schöier et al. 2002, Maret et al. 2004

15. Example: CH3OH jump abundance structureXJ
Jump
Freeze-out

16. Chemical richness low-mass YSOs
IRAS 16293
JCMT survey
Cazaux et al.
2003
Caux et al.,
In prep
Line density similar to that in high-mass YSOs
Which molecules are first generation evaporated ices, and which
are second generation produced in gas-phase?
- How are molecules liberated? Passive heating or shocks?

17. Starting to image the hot cores
CH3CN
HCOOCH3
Kuan et al. 2004, SMA
Schöier et al. 2004, OVRO
Bottinelli et al. 2004, PdB
Chemical differentiation found on small scales

18. Conclusions
A quantitative framework for the interpretation of the physical and chemical structure of protostars has been established on scales of AU
Outer envelope: chemistry controlled by CO freeze-out
- Depletion related to thermal/dynamical evolution=> t?
- Effect on other key species, e.g., HCO+ and N2H+
Inner envelope: chemistry controlled by evaporation ices
- Ices released by passive heating and/or shocks
- Small-scale structure (<1000 AU) important (disks, holes,..)

19. Future: Herschel and ALMA
Water observations
Main ice freezing-out and evaporating
Herschel HIFI, PACS => key program
Submilimeter interferometry
Direct imaging radial structure chemistry and physics
SMA, PdB, CARMA, ALMA: need multi-line
Deep mid-infrared studies
Warm dust inner envelope, outflow cavities
Spitzer, ground-based 8-m class
Detailed modeling
Chemical structure (forward modeling)
Coupling with dynamics (Lee et al. 2004)

20. H2O and HDO HDO 464 GHz JCMT H2O 557 GHz SWAS
IRAS 16293
H2O abundance jumps by factor of ~10?
HDO abundance jumps by factor of >100?
Stark et al. 2004
Parise et a. 2004

21. ISO water observations
Herschel will improve on ISO by orders of magnitude in
spatial and spectral resolution and sensitivity
Nisini et al. 1999
Ceccarelli et al. 1998