Chemical and Physical Structures
of Massive Star Forming Regions
Hideko Nomura, Tom Millar (UMIST)
ABSTRUCT
We have made self-consistent models of the
density and temperature profiles, and then
investigated the hot core chemistry after
grain mantle evaporation due to heating by
an embedded luminous object, taking into
account the different binding energies of
the mantle molecules. We find that the
resulting column densities are consistent
with most of those observed toward
G34.26+0.15 at a time around 104 yrs after
the central star formation. We have also
investigated the dependence of the density
profile on the chemical structures which
suggests an observational possibility of
constraining density profiles of hot cores
from determination of the source sizes of
line emission from desorbed molecules.
Chemical Network
211 species, 2190 reactions
Initial Condition
(evaporation of mantle molecules)
Physical & Chemical Properties of Hot Cores
7
-3
Size < 0.1pc, T ~100-300 K, nH ~ 10 cm
IR source, Outflow, Inflow
<-> Massive Star Formation
X(M, hot core)~10-103 X(M, dark cloud)
M: NH3, H2S, CH3OH, (CH3)2O etc.
(Kean
2000)
★
YSO
3
Ri=νiexp(-Ei/Td), τi ~1/ Ri~10 yr ->Td,i
Origin of Abundant Molecules in Hot Cores
prestellar star-formation
protostellar
H2O, CH3OH
NH3, CO2
evaporation of
freeze out & grain
icy mantle
surface reaction
evaporation of icy mantle
+ subsequent gas-phase reaction
-> complex molecules
H2S
CH4, CO
(from Hasegawa & Herbst 1993)
MODEL FOR G34.3+0.15
PHYSICAL MODEL
Molecular Column Densities
Density & Temperature Profiles
Density Profile
SED & Radial Profile of Radiation Flux
Central Star: L=5×105Ls
V
G31.41
CHEMICAL MODEL
INTRODUCTION
rcore =0.05pc
~1pc



0
Comparison with Obs.
N mol (t)   ds  dr 2π r n(r)
 x mol (r, t)exp( r /Δ
2
Time Evolution
t ~104yr
2
beam
)/ π
2
beam
Obs. of G34.3
Calculation
(3×104 - 3×105yr)
Core + Envelope Model
nH(r)25= n-20/(1+r/rcore)-1.5
NH=10 cm
(Hatchell et al. 2000)
Dust Temperature
Heating Source: Central Star
Local Radiative Equilibrium


4  dν κ ν Bν (T)   dν κ ν  I ν dφ dμ
0
0
Reemission
=
Absorption
Radiative Transfer Eq.
I ν  ρκ ν (Bν  I ν )
Gas Temperature
Thermal Equilibrium
G+L-L= 0 -> Tgas(r)
G : photoelectric heating on dust by FUV
L : heating & cooling by collision
between gas and dust particles
L : cooling by line excitations
Obs. from Macdonald et al. ’96,
Consistent with obs. of
SED for rcore= 0.05pc
GENERAL MODELS
- Dependence of Density Profile Density & Temperature
Profiles
Radial Profiles of
Molecular Abundances
Destruction of parent mol. & Hatchell et al. ’00, Ikeda et al. ’01
Consistent with obs. of
creation of daughter mol.
most mol. around t ~104yr
@ t ~104 -105 yr
OUTFLOW REGION
Outflow
(v~10km/s, NH=1024cm-2)
Hot core
(t =104yr, NH=1025cm-2)
SUMMARY
Chemical and Physical Structure
of Hot Core G34.3+0.15
Radiative transfer calculation
-> dust & gas temperature
+ Chemical calculation
(inc. temp. dependent dust evap.)
->
Calculated Nmol: consistent with obs.
@ ~104 yrs after the star formation.
Dependence of Density Profile
on Chemical Structure
-> observational possibility of
constraining
density profiles of hot cores
from source sizes of line emission
Chemical Model for Outflow Region
Density profiles <->
Temperature profiles
cf. kn n, r
r-p ->T∝r(p+1)/(4-n)
-> Obs. of dramatic changes
in mol. abundance due to
dust evaporation possibility
constrain density profiles
of hot cores
Destruction of some molecules
in inner hot region
Advection of molecules
to outer region