Radiative Transfer Flashcards
(31 cards)
What is Jy?
Janksy
It is a unit of spectral flux density, designed for the low energies of radio astronomy.
1Jy = 10^-26 W m^-2 Hz^-1
What is the integral for Energy?
dE = Iν dA dt dΩ dν
E: energy
Iv: intensity at a specific frequency
A: area
t: time
Ω: solid angle
ν: frequency
What is the integral for intensity?
dI = Iν dν
I: intensity
Iv: intensity at a specific frequency
ν: frequency
What is the integral for flux?
dF = Iν dΩ dν
F: flux
Iv: intensity at a specific frequency
Ω: solid angle
ν: frequency
What is the integral for luminosity?
dL = Iν dA dΩ dν
L: luminosity
Iv: intensity at a specific frequency
A: area
Ω: solid angle
ν: frequency
What is av?
Absorption coefficeint
m^-1
what is jv?
Emmission coeffficeint
W m^-3 Hz^-1 sterad^-1
What is τv?
Optical depth
What do different values of τv mean?
τ ≥ 1 optically thick (opaque)
τ «_space;1 optically thin (transparent)
What is the general radiative transfer equation?
Iν = I0 exp(-τv) +Sv(1-exp(-τv))
What is Sv?
Source function
= jv / av
What happens to the radiative transfer equation if the medium is optically thin?
τv «_space;1
exp(-τv) ≈ 1 - τ
What happens to the radiative transfer equation if the source is emmits thermally?
Sv = jv / av = B(v,T)
B(v,t): Plank’s black body function.
What happens to Plank’s black body function at low frequencies?
(exp(-hv/kT) -1) ≈ hv/kT
What is the equation for dust’s optical depth?
τv = kv NH μ mp
τv: optical depth
NH: column density of H atoms
μ: mean molecular weight
mp: mass of proton
What happens to the radiative transfer equation if there is no background source?
I0 = 0
What happens to the radiative transfer equation if the medium is optically thick?
exp(-τv) ≈ 0
What is the Lynman Series?
Hydrogen lines.
N=1 upwards
UV
What is the Balmer Series?
Hydrogen lines.
N=2 upwards
Visable
Halpha is N=2 and N=3
What is the Paschen Series?
Hydrogen lines.
N=3 upwards
IR
Where is Bremstrahlung Radiation found?
Local group: HII regions (cm and microwave)
Extragalactic: galaxy clusters (X-rays)
Where is Synchrotron Radiation found?
Local group: SN remnants (radio, IR, visible, x-ray), Diffuse ionised gas (radio).
Extragalactic: Galaxy jets (radio, X-ray)
What is Bremstrahlung Radiation?
Radiation which is emitted when an electron is accelerated by nuclei, through the Coulomb force.
What is the E field in Bremstrahlung?
E = (q |a| sinθ ) / (4 π ε₀ r c^2)
E: E field strength
q: charge
a: acceleration of charge
θ: angle between the direction of movement and the observer.
r: distance from charge
