Classification Of Stars Flashcards
Define a black body.
A black body is one that absorbs all radiation that falls on it; as a result it is also able to emit radiation at all wavelengths.
What is Wien’s Displacement Law?
Temperature of the body multiplied by the peak wavelength emitted by that body is equal to a constant. (λmaxT=2.90x10^-3mK)
What is Stefan’s Law?
The total energy radiated per unit time per unit surface area of a black body is proportional to the absolute temperature of the body to the fourth power. (E=σT^4)
Define luminosity.
Luminosity is the total energy emitted by a body per second.
Define apparent magnitude.
The apparent magnitude (m) of a body is a measure of is brightness as seen from Earth.
What is Pogson’s equation?
m = -2.5log(I) + K
Define absolute magnitude.
The absolute magnitude (M) of a body is a measure of its brightness after adjusting for distance. It is defined as the apparent magnitude the body would have if it were placed 10 parsecs from Earth.
What equation relates apparent and absolute magnitude?
m-M=5log(d/10)
How are stars classified and on what basis?
Stars are split into 7 classes (O B A F G K M) and this is based on the relative intensities of the absorption lines in their spectra.
Describe the surface temperature, colour and origin of prominent absorption lines in a type O star.
28,000K-50,000K; blue and ionised helium.
Describe the surface temperature, colour and origin of prominent absorption lines in a type B star.
10,000K-28,000K; blue-white and neutral helium and hydrogen.
Describe the surface temperature, colour and origin of prominent absorption lines in a type A star.
7,500K-10,000K; white and hydrogen.
Describe the surface temperature, colour and origin of prominent absorption lines in a type F star.
6,000K-7,500K; yellow-white and Ca+ and ionised metals.
Describe the surface temperature, colour and origin of prominent absorption lines in a type G star.
5,000K-6,000K; yellow and Ca+ and neutral metals.
Describe the surface temperature, colour and origin of prominent absorption lines in a type K star.
3,500K-5,000K; orange-red and molecules, Ca and neutral metals.
Describe the surface temperature, colour and origin of prominent absorption lines in a type M star.
2,500K-3,500K; red and molecules and Ca.
Why do only certain stars show prominent hydrogen absorption lines?
For hydrogen to absorb visible light (Balmer series) the hydrogen’s electron must start in the n=2 excitement level. If it starts in a higher level then it emits infrared or longer wavelengths, in a lower level it emits UV or shorter wavelengths. Ionised hydrogen cannot produce absorption lines as it has no electrons.
