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Astronomy
Observational, not experimental
Photos of objects
Spectrum
A non-equilibrium gas
 Gas
emitting spectrum has a very low density,
exposed to a range of radiation fields and particles
 Populations of levels, ionization, spectrum,
determined by many micro-physical processes
 Not characterized by a single temperature
H, He rich, some O, C, N, Fe etc
30
Atomic Number
25
20
15
10
5
0
1
1000
106
n(Z) / n(Si)
109
1012
Solar corona
 Collisional
 kT
equilibrium
~ iP
Fe XII
102
Stellar SED
Flux F
101
H0
He0
T = 40,000 K
*
100
10-1
10-2
500
1000
Wavelength (A)
1500
2000
Photoionization Equilibrium
 energetic
radiation interacts
with surrounding gas
– photoionization
 photoelectrons
heat free
electrons
 electrons excite heavy
elements
– collisionally excited line
cooling
 free
electrons recombine
– recombination lines
Cloudy
 Follows
the detailed microphysics, with most
processes treated at elementary level
 All stages of ionization of the lightest 30
elements, 100+ molecules
 2.7 K ≤ T ≤ 1010 K
 10-10 ≤ n ≤ 1015 cm-3
 Continuously maintained
 Fully open source, at www.nublado.org
- log fractional ionization
Temperature
10000
1000
100
0
1
C+2
He0
H+
He
2
+
C0
H0
molecular fractional
100
CO
10-1
H2
H2O
10-2
CH
10-3
OH
10-4
H2O
1.5e+17
1.6e+17
1.7e+17
1.8e+17
Depth (cm)
Ferland, G.J., 2003, ARA&A, 41, 517
1.9e+17
2.0e+17
1000
L
100
[O III]
[O II] H
[S III]
[O III]
[O III]
[Ne II]
[C II]
10
[N II]
Br
-2
-1
F (erg cm s )
P
1
0.1
0.01
0.001
0.1
1
10
Wavelength (microns)
100
1000
Cloudy on the web www.nublado.org
Some databases
 Originally
home-grown internal database,
hardwired into code
– Moving to all data external to code
 Collisional
ionization, Voronov 97, Dere 09
 RR & DR, Badnell web site, our data
 Chemistry largely based on UMIST
 H2 internal structure, lines, Meudon databases
 Heavy molecules, internal structure, lines,
Leiden LAMDA database
Collisional radiative cooling – Fe VII
Astronomy
Observational, not experimental
Photos of objects
Spectrum