Modeling
and Observations: 50
"Confronting astrochemical models and observations"
Henning, Herbst, Semenov
a)
First detected species (1937-41, CH, CN, CH+, visual)
b) First species
found with radio-telescopes
(196?, OH)
c) First chemical
models (Bates & Spitzer 1951, Herbst &
Klemperer 1973)
d) Cloud models/disk
models & observations (antenna/interferometer)
e) Dynamical effects
& observations
f) Recent progress
& predictions for the future?
a) Chemical
processes in space:
- basic facts: cold, high
vacuum, a lot of H2, long times (t >> 1 year)
- bond formation, destruction, and rearrangement
- gas phase (ion-molecule, neutral-neutral, photo, CRP, RA,
DR, ...)
- gas-grain interactions (accretion, desorption,
PAHs)
- catalytic reactions on dust surfaces (H2)
- isotope fractionation (or in another section?)
b) Astrochemical
databases:
- (history of)
UMIST, OSU, Meudon, ...
- some facts concerning Measured/Estimated/Theoretical rates
- scaling of the
rate constants to the room/10K temperatures
- rate uncertainties
c) Initial
abundances:
- "low/high
metals"
- molecular abundances
- hints from observations?
d) Numerical solvers?:
- Dense/Sparse
formalism, DVODE, LSODE, DVODPK, Limex, etc.
- accuracy, convergence, computational speed
a) First atoms &
molecules:
- recombination at z~1000, protons, e-, He, Li+
- major routes to form H2 without dust
- the role of "heavy" elements
b) Formation of
primordial "clouds":
- first concentrations toward dark matter halos?
- heating & cooling at high z: C/CO/H2O?
- dynamical aspects?
a) A small
introduction:
- ISM as a
multi-phase entity
- distinct components of ISM
- different regimes of chemistry
b) Diffuse &
translucent clouds:
- importance of photoprocesses (PDR,
shell/layered-like structure?)
- importance of clumpiness
- a CH(+) puzzle
- chemical content & evolution (age)
- various observable tracers
c) Dense clouds:
- dynamical evolution (contraction, stability, turbulence, amb. diffusion)
- freeze out
(depletion)
- importance of surface chemistry
- deuterium fractionation
- various observable tracers
d) Hot cores:
- release of surface materials
- rapid neutral-neutral chemistry
- slow heat-up phase & build up of complex molecules on
the surfaces
- various observable tracers
e) Large-scale
fractal structures in the Milky Way?
- GMC formation and
evolution (timescales, composition)
- Fractal
properties
- Dynamics, shocks?
a) Physical
structure:
- temperature gradients
- accretion heating
- flaring
- turbulence
- dust evolution
b) Line radiative transfer:
- critical densities
- non-LTE/LTE zones in disks
- radiatively coupled regions
- accurate approximate LRT approaches
c) Reconstruction of
disk parameters:
- emission lines = chemistry & excitation conditions
- Boltzmann diagram
(hyperfine components)
- minimization techniques (beam convolution vs. u,v-space)
- kinematics (first-order maps, P-V diagrams)
- T(r,z) => CO isotopes, NH3
- rho(r,z) => continuum, CS, etc.
- photo => CN/HCN/HNC, C2H
- ionization => HCO+, N2H+,
- deuterium frac. => DCO+, DCN
e) Chemical modeling:
- layered structure
- initial abundances?
- high-energy radiation (X-rays, UV, CRP)
- surface reactions & stochastic regime
- turbulence/global flows
- ?
Herbst, Henning, Semenov (5
pages)
a) Molecular clouds:
- bistability, hypersensitivity
- uncertainty as a function of molecular complexity
- typical error bars for observed species
- most problematic reactions
b) Circumstellar disks:
- typical error bars for observed species
- most problematic reactions