Main Sequence Stars Flashcards
What is flux?
The amount of light received per unit area at a given distance from a star
What is apparent magnitude?
The brightness of an object as it appears from Earth (depends on both luminosity and distance)
What is absolute magnitude?
The brightness and object would have if it were at 10pc (depends only on intrinsic luminosity)
What is the principle distinguishing feature of stars?
Stellar temperature
Put spectral types in descending temperature order
O B A F G K M R N S
Describe B stars
•11000-30000K
•most of H ionised so only very weak H lines
Describe A stars
•7500-11000K
•ideal excitation conditions, strongest H lines
Describe G stars
•5200-5900K
•too cool, little excited H, so only weak H lines because electrons mostly in ground state
Why are spectral lines in fainter stars broader?
•temperature fixed for a given spectral class
•therefore brighter star must be bigger, meaning the absorbing atoms further from star where the density and pressure is lower, narrower lines
What are Mall classifications?
•Ia=bright supergiants
•II=bright giants
•IV=subgiants
•Ib=supergiants
•III=giants
•V=dwarfs
What did spectral classification provide?
A way to link the observable features to physical characteristics of stars
What defines the main sequence?
Mass
•more mass means more gravitational pressure means more hydrogen needs to be fused into helium to increase thermal pressure to maintain hydrostatic equilibrium
What is the main sequence turnoff?
When older star clusters no longer have any high mass stars left
