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Chemical Models of High Mass Young Stellar Objects

Great Barriers in High Mass Star Formation. Chemical Models of High Mass Young Stellar Objects. H. Nomura 1 and T.J. Millar 2 Kyoto Univ. Japan, 2. Queen’s Univ. Belfast, UK. §1 Introduction. Mm/sub-mm Obs. of Mol. Lines. Orion KL, SMA. (Beuther et al. 2005, 2006). CH 3 OH. CH 3 OCH 3.

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Chemical Models of High Mass Young Stellar Objects

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  1. Great Barriers in High Mass Star Formation Chemical Models of High Mass Young Stellar Objects • H. Nomura1 and T.J. Millar2 • Kyoto Univ. Japan, 2. Queen’s Univ. Belfast, UK

  2. §1 Introduction

  3. Mm/sub-mm Obs. of Mol. Lines Orion KL, SMA (Beuther et al. 2005, 2006) CH3OH CH3OCH3 SO2 13CH3CN IRc6 I SMA1 HC n Compact Ridge IRDC18223-3, SMA CH3OH Unidentified lines (Fallscheer et al. 2009)

  4. Infrared Obs. of Molecular Lines Small hydrogenated, saturated molecules AFGL 2591 by ISO Orion KL by ISO C2H2 n5 HCN n2 (Lerate et al. 2006) (Lahuis & van Dishoeck 2000) Orion KL by Herschel/HIFI NGC7538IRS1 by IRTF/TEXES (Knez et al. 2009) (Crockett et al. 2010)

  5. Origin of Abundant Molecules in HC H CH3OH ★ ☆ O CO H2O S H2S X(M, hot core)~10-103 X(M, dark cloud) M: NH3, H2S, CH3OH, (CH3)2O etc. Young Stellar Evolution protostellar &outflow(shock) star-formation prestellar freeze out & grain surface reactions evaporation of icy mantles evaporation of icy mantles +subsequent gas-phase reactions abundant complex molecules

  6. Obs. of Icy Mantle Molecules W33A by ISO O H2O N NH3 CO CH3OH H O CO N L1498 by IRAM Obs. Dust continuum H CO (Caselli+ 1999, Tafalla+ 2004, …) SVS 4-5 by Spitzer CH3OH & NH3 (Gibb et al. 2000) (Bottinelli et al. 2010) Hydrogenated, saturated molecules in ice (e.g., Spitzer: Boogert+ 2008, Pontpiddan+ 2008, Oberg+ 2008, AKARI: Aikawa+ 2009)

  7. Grain surface chemistry Surface reactions in laboratory H CO grain surface (Charnley 1997, 2001, 2005) (e.g., Watanabe & Kouchi 2008) Amino acids? ... High mass YSOs are good targets for test

  8. Hot Core Mol. in Various Objects H2S SMA IRAS 16293-2422 Starburst galaxies IRAM NGC253 (Cazaux et al. 2003) (Minh et al. 2007) CMZ of Galactic Center CH3OH C2H3CN (e.g., Requena-Torres+ 2008) Nearby extragalaxies NGC253, NGC4945, M82, IC342, Marrei2, NGC6946 ~500AU SMA (e.g., Martin et al. 2006, 2008) Grain surface chemistry seems universal (Kuan et al. 2004)

  9. §2 Hot Core Chemistry

  10. Hot Core Chemistry – Cold & Hot Protostellar Prestellar Grain surface T~10K C, O, N, S, CO, … Gas-phase reactions T>100K thermal evaporation from grains H grain surface H2O H3O+ destroy molecules CH4, C2H2carbon-chain mol. NH3 HCN, HC3N, CH3CN, … Hydrogenated, saturated molecules CH4, H2O, NH3, H2S, CH3OH, … H2S SO, SO2, … CH3OH CH3OCH3, HCOOCH3, … (Charnley+ 1992, Millar+ 1997, …) grain surface

  11. Hot Core Chemistry – Warm CH3OH2++H2CO HCOOCH3 : inefficient (Horn et al. 2004) Surface reactions in laboratory Grain surface T~40K CH3, HCO, … CH3O grain surface unsaturated molecules CH3OCH3, HCOOCH3, … UV UV (e.g., Hasegawa+ 1992, Garrod+ 2006, 2008, …) (Oberg et al. 2009) Thermal history & UV photons in star forming cores?

  12. §3 Physical and Chemical Models of High Mass YSOs

  13. Physical & Chemical Models of YSOs Physical structure (Tdust, Tgas, rgas, vgas) radiative transfer T, hydrodynamics r, v + constraint Chemical reaction network gas-phase, grain surface, gas-grain interaction + ⇔ Line radiative transfer comparison with obs. UV Tgas vgas Tdust Thermal evaporation Mobility on grains Get rid of activation barrier of reactions Transport molecules & dust grains UV + + ★ grain surface

  14. Chemical Structure of YSOs Mantle mol. r ★ CH3OH H2CO H2O HCN HCOOCH3 CH3CN 104yr r [pc] H2O, CH3OH H2O, CH3OH NH3, CO2 Tdust NH3, CO2 H2S, O2 Tdust H2S O2 CH3OH H2CO HCOOCH3 HCN CH3CN 104yr r [pc] Molecules are abundant at cloud center (Nomura & Millar 2004)

  15. Effect of vinfall on low mass YSO chem. CH3OH CH3OCH3:tgas-phase chem > tinfall tgas-phase chem~104-5yr, tinfall~103yr (~300AU/1km) Another pathway to unsaturated molecule formation? physical model radiative hydrodynamic simulation t [yr] t [yr] Warm grain surface reactions respond to formation of unsaturated molecules? (Aikawa+ 2008)

  16. Dependence on warm-up time High mass:tstar<105yr Low mass:tstar>107yr T [K] T [K] Short (5x104yr) Long (1x106yr) HCOOH (ice) HCOOH (ice) HCOOH (gas) HCOOH (gas) t [yr] t [yr] gas-phase reaction grain surface reaction HCOOHformation (Garrod + 2008) Abundances of unsaturated molecules in gas & ice Grain surface chemistry & Stellar evolution time ?

  17. Chemical Structure of Young Disks surface CH3OH H2O H O CO NH3 N (e.g., Markwick+2002, Aikawa+ 2002, Bergin+ 2007) outer disk CN, C2H HCN, H2CO, etc. UV,X-rays accretion near midplane inner disk dust dust (Walsh, Millar, HN 2010, in press) CO R<10AU Photo- dissociate CO R<300AU Frozen- out Warm grain surface reactions during accretion?

  18. Chemical Structure of Young Disks NH3, no motion (low mass star) (Heinzellar, HN, Walsh, Millar 2010, in prep.) Photo- evaporation? NH3, vertical motion (low mass star) (Okamoto+ 2009) Transport of mol. from disk midplane to surface layer Diagnose high mass disk chemistry & physics by ALMA

  19. §4 Summary Hot Core Chemistry Grain surface reactions + desorption from grains + gas-phase reactions Grain surface chemistry seems universal Physical & chemical models of high (& low) mass YSOs Certain molecules are abundant near central star Role of warm surface chemistry? Dependence on warm-up time Stellar evolution, accretion velocity in disks Diagnose physics & chemistry of YSOs by ALMA __

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