Section 4: Stellar atmospheres Flashcards
(24 cards)
What is the equation for absorption intensity through a medium?
dIλ/dz=-κλρIλ
What is the equation for scattering intensity through a medium?
dIλ/dz=-σλρIλ
What is the equation for emission intensity through a medium?
dIλ/dz=ελρ
What is the equation for the mean free path of a photon?
l=1/κλρ
What is the optical depth?
dτλ=κλρdz
What is the ratio of I(Z) and I(0)?
I(Z)/I(0)=e-κρz
What are Bound-Bound transitions?
Energy level transitions
What are Bound-Free absorptions?
Ionisation
What are the types of line broadening?
Natural
Doppler
Pressure
What is natural broadening?
Comes from the uncertainty principle
ΔEΔt=ℏ
What is Doppler broadening?
Comes from the motion of the absorbing atom
What is the equation for doppler shift?
Δλ/λ=v/c
What is the most probable speed for an atom?
Vprob=sqrt(2kBT/m)
What is pressure broadening?
Comes from uncertainty principle
Δt decrease and so ΔE increases
What is Kramer’s law?
κ α ρT-7/2
What are the types of scattering?
Rayleigh-elastic
Compton-inelastic
Thompson-elastic
What is the Radiative Transfer Equation?
dIλ/dτ=Iλ-Sλ
What is local thermal equilibirum?
For a region, the temperature is constant and the Maxwell-Boltzmann distribution is followed
How are emission lines explained using LTE?
Hot gas, not dense enough for pure black body
How are absorption lines explained using LTE?
Dense black body emitter, with cold gas in front of it
What is the equation for radiation pressure?
Prad=4σ/3c T4
Where does radiation pressure come from?
Photons carry momentum and reflect off of a surface
What is the intensity of a black body emitter?
I=σT4/π
What is Limb darkening?
A star is hotter towards its core and so the edges have lower intensities and redder wavlengths
