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(2) Stars > Stellar Atmospheres Part 1 > Flashcards

Stellar Atmospheres Part 1 Flashcards

1
Q

What is it called when something transitions between energy states?

A

Bound-bound transitions.

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2
Q

What are the 4 quantum numbers?

A

n, l, s, mz

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3
Q

What is the quantum state m a function of?

A

m = m(n, l, s, mz)

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4
Q

What is the equation for Nm, the particle density at level m?

A

Nm = N1/g1 * gm*exp(Em/kT)

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5
Q

What is the partition function U(T)?

A

U(T) = sum from m=1 to inf of gm*exp(_em/kT)

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6
Q

How do we incorporate the partition function into the equation for Nm?

A 
-Change Nm to N and add a 
sum infront of the exponential
-Sub in U(T)
-Rearrange for N1
-Sub back into equation for Nm
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7
Q

How do electrons create absorption lines?

A

Free electrons can have range of kinetic energies, so bound free transitions produce continuous opacity (absorption)

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8
Q

What is needed to ionise an atom from a given level.

A

A minimum photon energy.

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9
Q

What does the Saha equation give?

A

The distribution of atoms in different stages of ionisation.

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10
Q

What is the equation for the energy difference between ground state and free electron having velocity u?

A

ΔE = χ1 + 1/2 * m(e)*(v^2), where χ1 is the ionization potential and the second part is the KE of electron.

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11
Q

What is the difference between the Saha and the Boltzmann equation?

A

Saha gives the ionisation equilibrium, whereas Boltzman gives the excitation equilibrium.

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12
Q

What is the equation for the statistical weight of an electron, ge?

A

ge = 2dx1dx2dx3dp1dp2dp3/h^3, where dx1dx2dx3 = 1/Ne (Ne = electron density)

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13
Q

What does the Saha equation show?

A

The number of electrons which are completely disassociated with its original atom and now travelling freely through a star.

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14
Q

What does the Boltzmann equation show?

A

Used to calculate the distribution of a specific ion/atom over the available energy levels.

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15
Q

What are the layers of the sun?

A

Core, radiative zone, interface layer, convective zone, surface.

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16
Q

What is the equation for energy in terms of radiation transfer?

A

Intensityareatimewavelengthangle subtended by detector.

17
Q

What is the equation for intensity I(λ)?

A

I(λ) = B(T) = 2hc^2/λ^5 * 1/(exp(hc/λkT)-1)

18
Q

What is the integral equation for the flux?

A

F = integral of I(λ)*cosθ dΩ

19
Q

What is the equation for the absorption of intensity dI(λ)?

A

dI(λ) = -κ(λ)*I(λ) dz, where κ(λ) is the absorption coefficient and dz is the path length.

20
Q

What is the equation for the scattering of intensity dI(λ)?

A

dI(λ) = -σ(λ)*I(λ) dz, where σ(λ) is the scattering coefficient

21
Q

What is the equation for the emission of intensity, dI(λ)?

A

dI(λ) = ε(λ) dz, where ε(λ) is the emission coefficient. ε(λ) = κ(λ)*B(T)

22
Q

How is emission related to absorption?

A

dI(λ)emission = -dI(λ)absorption

23
Q

What is the energy of a photon released when a BB transition occurs equal to?

A

hv = Em-En

24
Q

What are the absorption lines in stellar spectra?

A

They show bb transitions.

25
Q

What is the equation for ΔE, the uncertainty principle in natural broadening? What does this mean?

A

ΔE ~ h/(2π*Δt). The energy levels are ‘fuzzy’.

26
Q

What do fuzzy energy levels mean?

A

Atoms can absorb photons with slightly different energy.

27
Q

What is the equation for Δλ?

A

Δλ = λ^2/2πcΔt

28
Q

What is the equation for velocity distribution of atoms (Maxwell-Boltzmann)?

A

v = sqrt(2kT/m)

29
Q

What is the equation for dopller shift?

A

Δλ/λ = v/c

30
Q

What is the difference between natural broadening and doppler broadening?

A

Natural is due to the fuzziness of the energy, whereas doppler is due to the doppler shifted frequencies.

31
Q

What is pressure/collisional broadening?

A

Interaction between particles.

32
Q

What do wide/narrow absorption lines represent on Flux-wavelength graphs?

A
  • Wider lines = main-sequence: small radius, high pressure

- Narrower lines = supergiant: large radius, low pressure

33
Q

How does the rotation of the star effect the absorption lines?

A

There is a constant Doppler shift along stripes parallel to the projected rotation axis. Faster the rotation, the broader the absorption lines.

34
Q

What is bound-free transition and what is the equation for hv?

A

Produces continuous absorption. Ionisation: produces ‘absorption edges’ at ionisation points.
hv = E(inf)-En + 1/2 * mv^2

35
Q

What does a graph of κ/ρ againt wavelength look like for different temperatures?

A

Linearly upwards with shard ‘ionisation edges’. Ionisation edges go further down for lower temperature.

36
Q

What is the equation for hv for free-free absorption?

A

hv = 1/2me(v2^2-v1^2)

37
Q

How do we get the total absorption coefficient?

A

κ = κ(bb)+κ(bf)+κ(ff)

38
Q

What kind of transitions are continuous absorption and line absorption?

A
  • Continuous: bf and ff transitions

- Line: bb transitions

(2) Stars (12 decks)

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