Paola Caselli INAF - Osservatorio Astrofisico di Arcetri

1. Molecole complesse in regioni di formazione stellare Paola Caselli INAF - Osservatorio Astrofisico di Arcetri Gas phase and surface chemistry (basic concepts)  From cold gas to protoplanetary disks: - pre-stellar cloud cores - protostellar (hot) cores - protoplanetary disks  Summary

2. Interstellar Molecules New molecules ! CH2CHCHO (propenal) CH3CH2CHO (propanal) (Hollis et al. 2004) Ehrenfreund & Charnley 2000, ARA&A, 38, 427 137 molecules have been detected in space (205 including isotopomers, 50 in comets)

3. Examples of gas phase chemistry H3+ O OH+ H2 H2O+ H2 H3O+ e e e H2O O OH O O2

4. Surface Chemistry (i.e. the chemistry on the surface of dust grains)

5. TYPES OF SURFACE REACTIONS REACTANTS: MAINLY MOBILEATOMS AND RADICALS A + B AB association H + H H2 H + X XH (X = O, C, N, CO, etc.) Accretion WHICH CONVERTS O  OH  H2O C CH  CH2  CH3  CH4 N  NH  NH2  NH3 CO  HCO  H2CO  H3CO  CH3OH 10/[Tk1/2 n(H2)] days Diffusion + Reaction tqt(H) 10-5-10-3 s Watson & Salpeter 1972; Allen & Robinson 1977; Pickes & Williams 1977; Tielens & Hagen 1982; d’Hendecourt et al. 1985; Hasegawa et al. 1992

6. Star formation

7. Pre-stellar cores

8. Pre-stellar cores: chemical properties C17O(1-0) CO disappears from gas phase at R < 7000 AU Caselli et al. 1999 N2D+(2-1) Ward-Thompson et al. 1999 N2 does not freeze-out as fast as CO N2H+ well traces the core nucleus D-fractionation increases towards the core center.

9. In pre-stellar cores: high degree of deuterium fractionation and molecular freeze out (Bacmann et al. 2003; Crapsi et al. 2004) H3+ + HD  H2D+ + H2 + E (Watson 1976) H2D+ + N2 (CO)  N2D+ (DCO+) + H2 H2D+ / H3+increases if the abundance of gas phase neutral species decreases (Dalgarno & Lepp 1984) 1. [H2D+] ~ [H3+] 2. CNO-bearing molecules are almost completely ( 98%) frozen within R Caselli et al. 2003, A&A, 403, L37

10. Summary on pre-stellar cores CO,HCO+ Vastel et al. 2004 H3+ N2,N2H+ H2D+ D2H+ D2H+ H2D+ D3+ e- H+ H2 2,500 AU 7,000 AU Roberts et al. 2003, 2004 Walmsley et al. 2004 15,000 AU Within the “molecular hole” (r ~ 2500 AU), dust grains are probably covered by thick iced mantles, which boost grain coagulation and where complex molecules form.

11. After protostellar birth: Van Dishoeck 2004, ARA&A

12. Hot Cores Around massive stars: D  20,000 AU; n(H2)  107 cm-3 ; T  100 K Around low-mass stars: D  300 AU; n(H2)  106 cm-3 ; T  50 K Chemical Properties: H-rich complex N-bearing and O-bearing molecules: CH3CN, CH2CHCN, CH3CH2CN, CH3OCH3, HCOOCH3, C2H5OH.. (e.g. Blake et al. 1987; Cazaux et al. 2003) Chemical differentiation (e.g. Wright et al. 1996) Orion KL

13. The Orion (N-rich) Hot Core and (O-rich) Compact Ridge Boonman et al. 2003 Hot Core Compact Ridge

14. Mostly simple saturated species The Orion Hot Core and Compact Ridge (Caselli, Hasegawa & Herbst 1993) Compact Ridge O N G R A I N S U R F A C E S 20 K 40 K Mostly complex N-bearing species Hot core

15. Best agreement with observations

16. Compact Ridge after mantle evaporation CH3OH CH3OCH3

17. Protoplanetary Disks

18. UV Chemical Structure of PPDs surface intermediate midplane Surface layer : n~104-5cm-3, T>50K Photochemistry Intermediate: n~106-7cm-3, T>40K Dense cloud chemistry Midplane: n>107cm-3, T<20K Freeze-out Aikawa et al. 2002; Markwick & Charnley 2003

19. Low molecular abundances Freeze-out@ cold dense region High CN/HCN ratio Photochemistry@ disk surface Molecular Abundances of PPD (Dutrey et al. 1997) DCO+ (van Dishoeck et al. 2003) and H2D+ (Ceccarelli et al. 2004) detected.

20. SUMMARY Pre-stellar cores: gas phase: CO, HCO+, HC3N, N2H+, NH3, N2D+, H2D+,D2H+ solid phase: formation of simple ices (H2O, CO,H2CO,CH3OH) Protostellar cores: saturation of complex species on surface Hot Cores: CH3CN,HCOOCH3, complex saturated molecules PP Disks: CO, CN, HCN, N2H+, HCO+, DCO+, H2D+ complex species ? Not yet detected.. A L M A