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Ruud Visser Leiden Observatory Ewine van Dishoeck, Steve Doty, Kees Dullemond, Jes Jørgensen, Christian Brinch, Michiel Hogerheijde, John Black November.

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Presentation on theme: "Ruud Visser Leiden Observatory Ewine van Dishoeck, Steve Doty, Kees Dullemond, Jes Jørgensen, Christian Brinch, Michiel Hogerheijde, John Black November."— Presentation transcript:

1 Ruud Visser Leiden Observatory Ewine van Dishoeck, Steve Doty, Kees Dullemond, Jes Jørgensen, Christian Brinch, Michiel Hogerheijde, John Black November 2, 2009 Chemical evolution from cores to disks

2 Low-mass star formation Evolution of gas and dust Herbst & van Dishoeck (2009)

3 Main features of this study One model from pre-stellar core to circumstellar disk Two-dimensional, axisymmetric Study chemical evolution  Goal in itself  Chemistry affects physics: temperature, MRI,...  Diagnostic tool

4 Motivation How do size and mass of disk evolve? When is the disk first formed? How does matter flow from envelope to disk? Explain observed cometary abundances Existing models  treat only the envelope or only the disk, or both in 1D  often approximate temperature

5 Comets: a view of the past Error bars indicate spread between sources Dotted line: hypothetical one-to-one relationship Comets in general similar to ISM, but individual differences exist Bockelée-Morvan et al. (2000, 2004), Schöier et al. (2002) CH 3 OH H 2 CO CO HCOOH HNC HCN

6 Analytical star formation model in 2D Fast to run, high resolution, easy to change initial conditions Cloud mass, rotation rate, sound speed,... Density & velocity: inside-out collapse Shu (1977), Terebey, Shu & Cassen (1984) Dust temperature (important!) from full radiative transfer RADMC: Dullemond & Dominik 2004 Physics compare well with hydrodynamical models Yorke & Bodenheimer 1999, Brinch et al. 2008a,b Density profiles compare well with observations Jørgensen et al Visser et al. (2009), Visser & Dullemond (subm.), Visser et al. (in prep.)

7 From one to two dimensions Visser & Dullemond (subm.) streamlines disk surface Previous collapse models treated disk as completely flat Include vertical structure: accretion occurs further out

8 Where does material go to? Start of collapse End of collapse into star/ outflow Inside-out collapse gives a layered disk Visser et al. (2009)

9 Infall trajectories Need to solve chemistry dynamically: compute n, T along many trajectories Many different trajectories Jump in n, T upon entering disk Visser et al. (2009), Visser et al. (in prep.) entering disk

10 Chemical evolution along one trajectory A:volatiles evaporate (e.g. CO, N 2 ) B:intermediates evaporate (e.g. CH 4, NO) C: other ices evaporate (e.g. H 2 O, NH 3, CH 3 OH) photodissociation of many species D: some species reformed Visser et al. (in prep.) disk surface outflow wall infall trajectory

11 Chemical zones: CO gas/ice Red: CO remains adsorbed (pristine!) Green: CO desorbs and re-adsorbs Start of collapse End of collapse Pink: CO desorbs and remains desorbed Blue: multiple desorption/adsorption Visser et al. (2009) into star/ outflow

12 Chemical evolution of water 1.Always frozen 2.Evaporates, photodissociated, reformed, freezes out 3.Evaporates, photodissociated, reformed 4.Evaporates, photodissociated 5.Evaporates 6.Evaporates, freezes out, evaporates 7.Evaporates, freezes out Visser et al. (in prep.) H 2 O ice H2OH2O O H2OH2O Before collapse: water frozen out onto cold dust

13 Chemical evolution of water 1.Always frozen 2.Evaporates, photodissociated, reformed, freezes out 3.Evaporates, photodissociated, reformed 4.Evaporates, photodissociated 5.Evaporates 6.Evaporates, freezes out, evaporates 7.Evaporates, freezes out Visser et al. (in prep.) Before collapse: water frozen out onto cold dust

14 Chemical evolution of water 1.Always frozen 2.Evaporates, photodissociated, reformed, freezes out 3.Evaporates, photodissociated, reformed 4.Evaporates, photodissociated 5.Evaporates 6.Evaporates, freezes out, evaporates 7.Evaporates, freezes out Comet-forming zone Visser et al. (in prep.) Before collapse: water frozen out onto cold dust

15 Implications for comets Dotted line: hypothetical one-to-one relationship Many model abundances differ from cometary abundances Suggestive of mixing or grain- surface chemistry? CH 3 OH H 2 CO CO HCOOH HNC HCN Visser et al. (in prep.) grain-surface chemistry

16 Another application of our model: dust Carbonaceous material  Graphite (small-scale limit: PAHs)  Hydrogenated amorphous carbon  Diamonds Silicates  Amorphous (olivine, pyroxene,...)  Crystalline (forsterite, enstatite,...) Ices  H 2 O, CO, CO 2, CH 3 OH, NH 3,...

17 From crystalline to amorphous and back 0–2% crystalline 1–30% crystallineup to 50% crystalline

18 Dust processing ISM: 1% crystalline; disks: 1–30% crystalline Crystallization by thermal annealing requires 800 K  Works for material accreting close to the star Crystalline silicates observed down to 150 K and in comets formed in 100–200 K regions How can we explain these cold crystalline silicates?

19 Disk evolution model Inside-out collapse with rotation Dust accreting in hot inner region is crystallized Disk spreads out to conserve angular momentum Crystalline material transported to colder areas Dullemond, Apai & Walch (2006), Visser & Dullemond (subm.)

20 Crystalline fractions Visser & Dullemond (subm.) time Black: 2006 model Red: new model 3.2 Myr 1.0 Myr 0.3 Myr obs. Model results in good agreement with observed range!

21 Observations Model Silicate dust  Partially crystalline  Partially amorphous Chemical composition  Generally similar to ISM  Individual differences Silicate dust  Partially crystalline  Partially amorphous Chemical composition  Outer disk unprocessed  Inner disk processed Implications for comets Cometary material is of mixed origins

22 Caveats Gas temperature  Gas-phase production of water  Increase inner-disk scale height Shape of stellar spectrum  Allow photodissociation of H 2, CO, N 2 Trapping of volatiles in water ice  Increase ice abundances of CO, N 2, O 2,... Mixing  Chemical zones in disk more diffuse Crystallinity paradox?

23 Future work Compute line profiles  Compare with observations by SMA, JCMT, IRAM 30m,...  Analyse water data from Herschel (WISH key program)  Make predictions for ALMA Add grain-surface chemistry  Formation of complex organics Add isotope-selective CO photodissociation  New model: Visser, van Dishoeck & Black (2009)

24 Conclusions First model to go from pre-stellar cores to circumstellar disks in 2D Important to do collapse and disk formation in 2D Disk is divided into zones with different chemical histories  Outer part pristine, inner part processed Cometary material is of mixed origins


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