3: STARS IN GALAXIES Flashcards
What is the order of MS stars and how are they ordered?
Ordered by decreasing temperature.
O, B, A, F, G, K, M
How do the top end of the MS stars (O, B) differ from the lower end (M) stars?
O and B are massive, hot, blue, high luminosity stars and M stars are cool, red, low luminosity stars.
What shape does the spectra roughly match?
A black body
What is the average temperature for O, G, and M stars?
> 30, 000 K
6000 K
< or = to 3000 K
What does B-V equal for the bluest stars compared to the reddest?
B-V = -0.3
B-V = -1.5
How are colours expressed?
Difference in their magnitudes in wavelength bands
In which star are the Balmer lines weakest/strongest and why?
Balmer lines aren’t that strong in O stars as the hydrogen is almost all ionised. Balmer lines max in A stars.
What causes Balmer lines?
The transitions between the first exited state and higher energy states of the electron
What causes weakness in Balmer lines?
Reducing the temperature.
What are the most important lines in G stars? (4)
The sodium D lines, the magnesium b feature, the G band of the CH radical, and the H and K lines of singly ionised calcium, CaII.
Define the 4000 A break.
The combined effect of the Balmer limit and the CaII and K lines sharply cutting off the spectrum
What is the 4000 A break a key feature of?
Intermediate temperature stars
How are luminosity and mass related?
L proportional to M to the power of alpha
What values do alpha take for M < 0.5 solar masses, M > 0.5 solar masses, and M > or = to 10 solar masses?
Alpha = 3
Alpha = 4
Alpha = 2
Define relationship for main sequence lifetime.
τms ∝ M/L ∝ M^(1-α)
Do high mass stars have a long lifetime?
No
Are main sequence stars the most important in generating light?
No, red giants are most important in some instances (e.g. in ellipticals)
Why are red giants luminous despite their low temperature?
Because they are big bois.
How is stellar population determined?
SFH and IMF
What is the Salpeter mass function relationship?
dN/dM ∝ M^(-2.35)
Why are older stellar populations redder?
Colour of overall stellar population becomes redder as we replace blue MS stars by red giants
What are Balmer lines also indicative of?
Age
In stellar populations with no recent SF, what dominates total light?
The red giants
How do old stars shed their outer layers and what does this affect?
Via stellar winds or the production of planetary nebulae or spectacularly in Type I or Type II supernovae. The processed material is returned to the ISM to be incorporated into the next generation of SF, producing stars of higher Z.
What do heavier elements effect?
Atoms/ions of metals absorb photons, so heavier elements absorb more light.
Where on the spectrum does absorption mainly occur? How does this affect appearance/metallicity?
The blue end of the spectrum. Stars with higher Z look redder than those of low Z
Lower mass galaxies have a lower escape velocity, so it’s easier for heavier elements to be lost via galactic winds. What does this mean for ellipticals?
There’s a correlation between Z and M for E galaxies
What colour is the disk/arms of a spiral and the colour of a bulge?
Disk/arms are blue
Bulge is yellow
What kind of stars occur in the disk/arms and what occurs in the bulge?
Population I stars in the disc/arms
Population II stars are in the bulge
Is Population II older than Population II?
Yes
Where are the older stars in the Galaxy?
Outer parts of the Galaxy
How are population II stars in the inner parts dispersed on Gyr timescales?
Gravitational interactions
How does the LF differ from IMF?
Translation between MS luminosity and stellar mass (via models of stellar structure)
What do clusters have an advantage over?
They have better sampling of very faint objects.
