Submm Survey of Low-mass Protostars: Tracing the physical and chemical structure and evolution

1. 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. 28 2004

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. SCUBA obs. + Rad. transfer model. Single-dish obs. + Monte Carlo model. Approach • CO • 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 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. “Canonical” CO abundance (Lacy et al. 1994) CO depletion: constant abundance 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. 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 L483:  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 16293-2422 Hot CH3OH gas JCMT Tex~80 K • CH3OH data can only be fitted if abundance jumps by factor of • 20-100 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 structure XJ 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 300-10000 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