Chemical Models of High Mass Young Stellar

Objects

Great Barriers in High Mass Star Formation

H. Nomura1 and T.J. Millar2

1. Kyoto Univ. Japan, 2. Queen’s Univ. Belfast, UK

§1 Introduction

IHC SMA1

n

IRc6

CompactRidge

(Beuther et al. 2005, 2006)CH3OH CH3OCH3 SO2

13CH3CN

Orion KL, SMA

Mm/sub-mm Obs. of Mol. Lines

Unidentifiedlines

(Fallscheer et al. 2009)

IRDC18223-3, SMA

CH3OH

AFGL 2591 by ISO

C2H2 5 HCN 2

(Knez et al. 2009)

Infrared Obs. of Molecular Lines

(Lahuis & van Dishoeck 2000)NGC7538IRS1 by IRTF/TEXES

Orion KL by ISO

(Lerate et al. 2006)

Small hydrogenated, saturated molecules

(Crockett et al. 2010)

Orion KL by Herschel/HIFI

Origin of Abundant Molecules in HC

☆★

evaporation of icy mantles+ subsequent gas-phase

reactions abundant complex molecules

prestellar

star-formation

protostellar&outflow(shock

)

freeze out & grain surface reactions

evaporation of icy mantles

Young Stellar Evolution

X(M, hot core)~10-103 X(M, dark cloud)

M: NH3, H2S, CH3OH, (CH3)2O etc.

O H CO

SH2O

CH3OH

H2S

Obs. of Icy Mantle Molecules

W33A by ISO

(Gibb et al. 2000)Hydrogenated, saturated molecules in ice

(e.g., Spitzer: Boogert+ 2008, Pontpiddan+ 2008, Oberg+ 2008, AKARI: Aikawa+ 2009)

Obs.

O H CO

N

O H2O

CO CH3OHN NH3

H

(Bottinelli et al. 2010)

CH3OH & NH3

Dust continuum

CO

(Caselli+ 1999, Tafalla+ 2004, …)

L1498 by IRAM

SVS 4-5 by Spitzer

Grain surface chemistry(e

.g., W

ata

nabe &

Kouch

i 2008)

(Ch

arn

ley 1

997,

2001, 2005)grain surface

COH

...Amino acids?

Surface reactions in laboratory

High mass YSOs are good targets for test

Hot Core Mol. in Various Objects

(Cazaux et al. 2003)

~500AU

CH3OH C2H3CN

(Kuan et al. 2004)

SMA

SMA

H2S

Starburst galaxies

(Minh et al. 2007)

(e.g., Martin et al. 2006, 2008)

NGC253

CMZ of Galactic Center(e.g., Requena-Torres+ 2008)Nearby extragalaxiesNGC253, NGC4945, M82, IC342, Marrei2, NGC6946

Grain surface chemistry seems universal

IRAS 16293-2422

IRAM

§2 Hot Core

Chemistry

Hot Core Chemistry – Cold & Hot

grain surface

C, O, N, S, CO, …H

Hydrogenated, saturated molecules

CH4, H2O, NH3, H2S, CH3OH, …

grain surface

(Charnley+ 1992, Millar+ 1997, …)

H2O H3O+ destroy molecules

NH3 HCN, HC3N, CH3CN, …

CH4, C2H2 carbon-chain mol.

H2S SO, SO2, …CH3OH CH3OCH3, HCOOCH3, …

Prestellar

ProtostellarGrain surface

T~10K Gas-phase reactionsT>100K

thermal evaporation from

grains

Hot Core Chemistry – Warm

unsaturated moleculesCH3OCH3, HCOOCH3, …

Thermal history & UV photons in star forming cores?(Oberg et al. 2009)

CH3, HCO, … CH3O

grain surface

(e.g., Hasegawa+ 1992,Garrod+ 2006, 2008, …)

Surface reactions in laboratoryGrain surfaceT~40K

(Horn et al. 2004)

UV

CH3OH2++H2CO HCOOCH3 : inefficient

UV

§3 Physical and

Chemical Models of High Mass

YSOs

Physical & Chemical Models of YSOs

Line radiative transfer comparison with obs.⇔

Chemical reaction network +

radiative transfer T, hydrodynamics , vPhysical structure (Tdust, Tgas, gas, vgas)

gas-phase, grain surface, gas-grain interaction+ co

nst

rain

t

grain surface+ +

Get rid of activation

barrier of reactions ★

Tdust Tgas vgas

Transport molecules & dust grains

Thermal evaporation

Mobility on grains

UV

UV

Chemical Structure of YSOs

Molecules are abundant at cloud center

CH3OH

H2CO

HCN

CH3CN

HCOOCH3

r [pc]

104yr

CH3OHH2CO

HCN

CH3CN

HCOOCH3

r [pc]

104yr

r★

(Nomura & Millar 2004)

Mantle mol.

H2O

H2O, CH3OHNH3, CO2

H2S, O2

H2O, CH3OH

NH3, CO2

H2S O2

Tdust

Tdust

Effect of vinfall on low mass YSO chem.

(Aikawa+ 2008)

CH3OH CH3OCH3 : gas-phase chem > infallgas-phase chem ~104-5yr, infall ~103yr (~300AU/1km)

Warm grain surface reactions respond to formation of unsaturated molecules?

physical model radiative hydrodynamic simulation

Another pathway to unsaturated molecule formation?

t [yr] t [yr]

Dependence on warm-up time

High mass: star<105yr Low mass: star>107yr

gas-phase reaction grain surface reaction

HCOOH formation(Garrod + 2008)

HCOOH (ice)HCOOH (gas)

Short(5x104yr)

t [yr]

T [K]

Abundances of unsaturated molecules in gas & ice

Grain surface chemistry & Stellar evolution time ?

HCOOH (ice)

HCOOH (gas)

Long(1x106yr)

t [yr]

T [K]

UV,X-rays

Chemical Structure of Young Disks

inner diskH2O CH3OH

NH3 dust

near midplaneO H

CON dust

outer diskCN, C2H

HCN, H2CO, etc.

surface(e.g., Markwick+2002, Aikawa+ 2002, Bergin+ 2007)

COR<300AU

COR<10AU

(Walsh, Millar, HN 2010, in press)

Photo-dissociate

Frozen-out

accretion

Warm grain surface reactions during accretion?

Chemical Structure of Young Disks

(Hein

zella

r, H

N,

Wals

h,

Mill

ar

20

10

, in

p

rep

.)

(Oka

moto

+ 2

009)

NH3, no motion(low mass star)

NH3, vertical motion(low mass star)

Photo-evaporation?

Transport of mol. from disk midplane to surface layer

Diagnose high mass disk chemistry & physics by ALMA

§4 Summary

Hot Core ChemistryGrain 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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