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Chemistry in low-mass star forming regions: ALMA ’ s contribution

Chemistry in low-mass star forming regions: ALMA ’ s contribution. Yuri Aikawa (Kobe Univ.). Collaborators: Hideko Nomura (Kobe Univ.) Hiroshi Koyama (Kobe Univ.) Valentine Wakelam (Obs de Bordeaux) Robbin Garrod (OSU)

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Chemistry in low-mass star forming regions: ALMA ’ s contribution

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  1. Chemistry in low-mass star forming regions: ALMA’s contribution Yuri Aikawa (Kobe Univ.) Collaborators: Hideko Nomura (Kobe Univ.) Hiroshi Koyama (Kobe Univ.) Valentine Wakelam (Obs de Bordeaux) Robbin Garrod (OSU) Paola Caselli (Arcetri) Eric Herbst (OSU)

  2. Contents • Chemical fractionation in prestellar • cores and molecular clouds • 2. From prestellar cores to • protostellar cores • 3. Protoplanetary disks • … talk by Guilloteau

  3. Chemical Fractionation in Prestellar Cores L1544 N2H+ CCS dust peak Ohashi et al. (1999) Depletion of C-bearing species - destruction of early-phase species (CS,CCS,..) in the gas phase - CO freezes-out onto grains tfreeze~ several105 (104 cm-3/nH) yr cf.tcont~ several 105 (104 cm-3/nH)1/2 yr non-depletion of N2H+ and NH3 - depletion of CO, which is the main reactant of N2H+ - slow formation of N2 Tafalla e al (2002 & talk) Aikawa et al. (2001; 2005) see also Maret et al. (2006)

  4. Deuterium enrichment in Prestellar Cores High molecular D/H ratios D2CO/H2CO=0.01-0.1 (Bacmann et al. 2003) N2D+/N2H+=0.2 cf. Elemental abundance: D/H ~ 10-5 @L1544(Caselli et al. 2003) … talk by Lis

  5. Mechanism of Deuterium Enrichment Exothermic exchange reactions H3+ + HD  H2D+ + H2 + △E1 L1544 HD2+andD3+ are produced subsequently CO depletion enhances H2D+ / H3+ H2D+ + e  H2 + D H2D+ + CO  HD + HCO+ gray: dust solid: H2D+ Vastel et al. (2006) Propagation by ion-molecule reactions in the gas phase H2D+ + X  XD+ + H2 Deuteration on grain surfaces Hydrogenation with abundant D atoms (originates in H2D+ + e  H2 + D) Exchange reactions of CH3OH on grain surfaces (Nagaoka et al. 2005) CH3OH + D CH2DOH + H, CH2 DOH + D CD2HOH + H, … If the core is heated … H2D+decreases rapidly H2D+ + H2 H3+ + HD … 104sec @T=50K, n(H2)=106cm-3 Other species (without direct exchange) survive to be observed in protostellar cores

  6. Variation among Cores L1544 L492 L1521B 10000 AU 10000 AU Dynamical evolution Chemical evolution Low D/H ratio Low D/H ratio High D/H ratio CCS central peak CCS central peak CCS central hole No depletion Small depletion? Significant depletion No NH3, N2H+ Central NH3, N2H+ Central NH3, N2H+ CCS No infall InfallInfall (Hirota & Yamamoto 2006, Crapsi et al. 2006, Aikawa et al. 2005, Tafalla & Santiago 2004, Lee at el 2003, Aikawa et al. 2001)

  7. Clumps and chemical differentiation in clouds H13CO+ CH3OH 15000 AU • Intensity distribution varies with species • Small clumps (~2000AU, 0.02Msun) inside cores • Gravitationally unbound • Correlation with physical condition is not yet found TMC-1C Talk by Takakuwa

  8. Chemical Fractionation: current: Depletion of CO and non-depletion of N-species Line survey towards CO-depleted cores (Tafalla et al. 2006) future: Deep look at the freeze-out region Statistics - correlation betweenphysical evolution chemical signature - difference between clouds Small clumpy structures - smallest size of clumps ? - correlation with physical structure ? Deuterium Enrichment: current: High D/H ratio towards prestellar/protostellar cores Spatial distribution of H2D+and HD2+ in prestellar cores future: H2D+and HD2+ observation by interferometer indicator of cores right before star-formation constraints on chemical reaction network Summary on Prestellar Cores

  9. From prestellar cores toprotostellar cores heating by accretion and a protostar compressional heating > cooling (by radiation) cold prestellar cores 1D radiation hydrodynamics Masunaga & Inutsuka (2000) temperature [K] log density [g cm-3] log r [AU] log r [AU]

  10. From prestellar cores toprotostellar cores heating by accretion and a protostar compressional heating > cooling (by radiation) cold prestellar cores 1D radiation hydrodynamics Masunaga & Inutsuka (2000) temperature [K] log density [g cm-3] log r [AU] log r [AU]

  11. From prestellar cores toprotostellar cores heating by accretion and a protostar compressional heating > cooling (by radiation) cold prestellar cores 1D radiation hydrodynamics Masunaga & Inutsuka (2000) temperature [K] log density [g cm-3] log r [AU] log r [AU]

  12. From prestellar cores toprotostellar cores heating by accretion and a protostar compressional heating > cooling (by radiation) cold prestellar cores As the core gets warmer… - Sublimation of ice - CO: 20 K - H2O: 160K - large organic molecules: 100K

  13. CO sublimates at 20 K Lee et al. (2004) CO -5 CS H2CO HCN log n(i)/nH -10 NH3 N2H+ HCO+ -15 -3 -2 -1 log r [pc] • - CO lines become observable again ! • CO kills N2H+ and NH3 • benefits CS and HCO+ CO sublimation freeze-out

  14. CO sublimates at 20 K • - CO lines become observable again ! • CO kills N2H+ and NH3 • benefits CS and HCO+ Sublimation radius R20K R100K prestellar ~1013cm-3 ~10 AU 1st core several 10 AU a fewAU 2nd core ~100 AU ~10 AU 9*104 yrs protostar several 103AU 100AU t=9x104yr second core t=0 CO sublimation larger organic species (ex. CH3OH) first core n ~1013 cm-3 t = -770yr Aikawa et al. (in prep) based on Masunaga & Inutsuka (2000)

  15. Complex Species in Low-mass Cores HCOOH (line contour) Remijan & Hollis (2006) - Detection of complex species toward IRAS 16293-2422, NGC1333… (talks by van Dishoeck and Sakai) - Abundances varies among cores - Some species are confined, some are extended - No evident dependence on CH3OH abundance - HCOOH/CH3OH is higher than in high-mass hot core Bottinelli et al. (2006) SMA observation of IRAS 16293-2422(Kuan et al. 2004)

  16. Complex Species in Low-mass Cores hydrogenation grain/ice surface grain/ice surface reaction between heavy species - How are they formed ? Molecules freeze-out on grains Grain-surface reactions e.g. CO  CH3OH (Watanabe & Kouchi 2002) grain-surface reactions during warm-up(Garrod & Herbst 2006) Gas-phase reactions of sublimates ex. CH3OH2+ + H2CO  HC(OH)OCH3+ + H2 inefficient(Horn et al. 2004) break-up in the recombination (Geppert et al. 2006)

  17. Calculation from a Prestellar to Protostellar Core Physical model of core contraction and protostar formation (Masunaga & Inutsuka 2000) Chemical model of gas & grain-surface reactions (Garrod & Herbst 2006) +  Distribution of gas and ice at each evolutionary stage Short warm-up phase: ~Rwarm/vinfall T > 20 K … 104yr T > 100K … 102yr 9 x 104yr after 2nd collapse Aikawa et al. in prep

  18. Calculation from a Prestellar to Protostellar Core Physical model of core contraction and protostar formation (Masunaga & Inutsuka 2000) Chemical model of gas & grain-surface reactions (Garrod & Herbst 2006) +  Distribution of gas and ice at each evolutionary stage Short warm-up phase: ~Rwarm/vinfall T > 20 K … 104yr T > 100K … 102yr gas phase 9 x 104yr after 2nd collapse ice mantle Aikawa et al. in prep

  19. Calculation from a Prestellar to Protostellar Core - Spatial Distribution CH3CN, HCOOH … extends to 1000 AU CH3OH, CH3OCH3 … sharp rise at 100 AU - Formation mechanism CH3OCH3 … formed from CH3OH via gas-phase reaction other species … combination of gas-phase and grain-surface reactions - The abundances are smaller than observed in IRAS16293-2422, NGC1333… gas phase 9 x 104yr after 2nd collapse ice mantle Aikawa et al. in prep

  20. Summary on protostellar cores As the core temperature rises… - heavy-element species migrate and react on grain surfaces - ice sublimates - sublimates react with each other in the gas phase  formation of larger molecules or destrcution current challenges: Interferometric observation of IRAS 16293-2422 - spatial distribution varies with species …why ? Observation of other low-mass YSOs (Talk by Sakai) - when the complex molecules become abundant ? - Difference between low-mass hot cores and high-mass hot cores Fully dynamical model with gas-phase and grain-surface reactions

  21. ALMA’s contribution on protostellar core High sensitivity detection of weak lines of complex species: 18.5hr@Nobeyama-45m vs 4 min@ALMA - How complex the interstellar molecules can be ? - More statistics

  22. ALMA’s contribution on protostellar core 2 x 104 high density warm slower infall Z [AU] complex species in disk (?) -2 x 104 -4 x 104 2 x 104 4 x 104 -2 x 104 x-y [AU] High spatial resolution - Derive molecular abundance without beam dilution - Spherical symmetry ? – NO! magnetic fields and rotation outflow, disk & envelope - Spatial distribution  formation mechanism - connection to disks and planetary systems Matsumoto & Tomisaka (2004)

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