Spectral Classes Flashcards
What is the Balmer Series?
A set of lines that represent the visible part of the emission/absorption spectrum of hydrogen
For a hydrogen absorption line to occur in the visible part of a star’s spectrum, what excitation level must electrons in the hydrogen atom already be in?
n = 2
How do hydrogen atoms in the n = 2 excitation level occur?
High temperatures, where collisions between atoms give the electrons extra energy
What happens to the excitation level if the temperature is too high?
The majority of the electrons will reach the n = 3 level
So there are no Balmer transitions
What is the density of the Balmer lines dependent on?
The temperature of the star
What is the order of the spectral classes?
O, B, A, F, G, K, M
What do astronomers do for the particular intensity of the Balmer lines for which two temperatures are possible?
Look at the absorption lines of other atoms and molecules
What spectrum is used for the Balmer series?
Spectrum of Hydrogen
What is the diagram of absolute magnitude against temperature called?
Hertzsprung-Russell
What are the three categories of stars?
White Dwarfs, Main Sequence, Red Giants/Supergiants
What spectral classes do White Dwarfs occupy?
half of O
all of B
a bit of A
What spectral classes do Main Sequence occupy?
half of O → all of M
What spectral classes do Red Giants/Red Supergiants occupy?
a bit of G → all of M
What is the absolute magnitude of White Dwarfs?
5 → 15
What is the absolute magnitude of the Main Sequence?
-10 → 15
