6.1

Question 1

Galactic Maps (Coordinates)

Answer 1

• l: galactic longitude (0-360 degrees)
• b: galactic latitude (-90 to +90 degrees)

Question 2

Star Light Attenuation

and what MW consists of

Answer 2

Star light is attenuated by interstellar dust.
MW consists of:
- stars
- Gas
- Dust

Question 3

Mean Number Densities of Stars

Answer 3

N(S) in stars/10⁶ pc³ for different spectral types.

not relevant unless we want to include table 1 on page 40 of notes

Question 4

Typical Stellar Parameters

Answer 4

• effective temperature (T_eff)
• luminosity (L/L_⊙)
• mass (M/M_⊙)

for different spectral types

Question 5

Stellar Mass Distribution

percentage per type

Answer 5

In the solar neighbourhood :

• ≈ 30% are G and K main sequence stars
• ≈ 30% M main sequence stars
• ≈ 30% white dwarfs

Question 6

Stellar Luminosity in Solar Neighbourhood

Answer 6

Dominated by:

• few higher mass stars
• red giants

Question 7

Sun’s Position

in regards to MW

Answer 7

The sun is near the mid-plane of the galactic disk.

Question 8

Star Distribution Perpendicular to Disk

how is it determined?

Answer 8

Determined by measuring fall-off of distribution for different stellar types.

it seems to have taken two subsequent bullet points as one being the reason for the next, not sure if thats correct

Question 9

Star Number Counts N(m)

Answer 9

N(m): number of stars brighter than apparent magnitude m.

Question 10

Distance Calculation for Stars

formula

Answer 10

d = 10^{0.2 · (m - M + 5)}

• d is the distance
• m is apparent magnitude
• M is absolute magnitude

Question 11

Star Counts Vertical to MW-Disk

Answer 11

N(m, S) shows deficit with respect to N(m) for m > m₀, depending on stellar type S. (because MW disk is thin)

Question 12

Vertical Distributions of Stars

Answer 12

N(z, S) = N(0, S) e^(-|z|/β)

with

• β disk scale height
• N(0,S) density in midplane

-> exponential falloff in the vertical direction

Question 13

Vertical Scale Heights and Surface Density

Answer 13

β_S [pc] and Σ_S [stars/pc^2] for different stellar types.

once again not relevant unless we include table 3 on p. 42

Question 14

Interstellar Extinction and Reddening

Answer 14

Caused by interstellar dust. Affects:

• apparent magnitudes (A_λ)
• colors of stars

Question 15

Extinction Curves

Interstellar; numerical value asked

Answer 15

• Approximation: A_V = 3.1 · E (B-V)
• Average for galactic plane A_V ≈ 1.5 mag/kpc

Question 16

Dust and Gas in MW

Answer 16

• mass of dust ≈ 0.005 of the mass of gas
• dust composed of:
  – silicates
  – carbon-rich particles

maybe another card for composition gas mostly: H and He - yes or add it here if its not too much