how bright a star appears from earth (not really very useful)
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absolute magnitude is
appartent magnitude of a star if it were 10 parsecs away
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describe abs. magnitude scale
-10 to +15, more negative, brighter, more positive dimmer (difference of 1 magnitude corresponds to ~ 2.5 times brighter)
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Spectral classes
O B A F G K M
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OBAFGKM -------> this direction is _________ temperature
decreasing, i.e O is hottest, and M is coolest
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Colours from OBAFGKM
blue, blue white, white, yellow white, yellow orange, red
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1 AU distance
this is the mean distance between the earth and the sun. 1 AU ≈ 1.5 × 10^11m
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1 pc distance
this unit of distance is derived from the parallax method of measuring stellar distances. 1 pc = 2 × 10^5 AU
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5 stages of star lifecycle
1. Protostar 2. Pre main sequence star. 3. Main sequence star. 4. Post main sequence star. 5. Death of star
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Protostar Formation (3)
(1) Within interstellar gas clouds, there are random fluctuations of particle density. (2) Grav. attraction between these atoms results in even greater density. (3) This attracts even more atoms. If this becomes big enough, may produce protostar.
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Energy in a protostar (3)
(1) as atoms in proto star become closer, they lose GPE. (2) this loss balanced by gain in KE (=rise in temp) (3) density of cloud sufficiently low for infrared to pass through it hence thermal E radiated.
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Pre Main sequence (3)
(1) As grav. collapse of proto star continues, becomes opaque to infrared. Thermal E trapped. Star heats up. (2) Heating increases internal pressure, resisting grav contraction. (3) Heat causes proto star to radiate heat/light weakly. This = PMS star
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Main sequence star (2)
(1) PMS continues to increase in T. T becomes sufficient to start fusion of H. Then it's MS. (2) if protostar too small ~
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Equilibrium in Main sequence (2)
(1) E radiated by star balances E produced in fusion - so T is constant. (2) radiation pressure otwards balances grav pressure trying to collapse star. Size constant.
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Post main sequence 1-3
(1) H used up. Eqbm broken. Core now mainly consists of He. (2) Core contracts reducing GE and increasing T. This increases rate of E output from core. (3) Increase in E output causes expansion. Then outer layers cool as expands. Red giant produced.
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Post main sequence con't 4-6
(4) core of red giant continues contracting, increasing T even further. (5) Fusion of He occurs, producing Be, C, O etc. (6) He burning maintains red giant in stable state for 10-20% of time spent in MS.
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Death more massive ___________ liftetime
shorter lifteime
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Death of core > 3 solar masses (main sequence mass > 15 solar masses)
bcauses black hole
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death mass
planetary nebula (sheds its outer layers of gas, eventually small hot and dense star white dwarf formed, this cools gradually and may eventaully porduce black warf
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death core mass 1.4 - 3 solar masses
Fusion of carbon, then neon, oxygen, silicon, which leads to Fe being produced, etc. Supernova, forming nebula
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Other cards in this set
Card 2
Front
apparent magnitude is
Back
how bright a star appears from earth (not really very useful)
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