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33 Cards in this Set
- Front
- Back
fundamental properties of stars
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distance
luminosity (intrinsic brightness) (total power) temperature |
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nearest star
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proxima centauri
3 star system |
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100 billion stars
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milky way galaxy
90% Hydrogen (atomic & molecular) 9% Helium 1% everything else (Carbon, Oxygen, Iron, dust ….) |
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100 billion gallexies
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universe
10^22 stars |
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trigonometric parallax
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objects closer to us appear to move more.....(d=1/p)
....distance (in parsecs)=1/parallax (arcsecs) most accurate for distance |
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parsec
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the distance at )which 1-arcsec subtends 1 A.U.....
1 pc = 3.26 Light-years =3x10^16m Typical separation between stars in galaxies is 1 parsec. |
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ways stars move
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In addition to Parallax
(Apparent motion) transverse component (proper motion) and line of sight component (dopler) |
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hipparchos (satellites)
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yielded accurate distances to over
120,000 stars. |
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inverse square law
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d1=1
d2=4 d3=9 Increasing a star’s distance by 3 means our eye receives 1/9th as much light. |
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luminosity function
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stars like sun, relatively common
high curve, low luminosity common low curve, high luminosity rare |
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black body
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stars emit light like a black body; temperature gives off color
|
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photometry
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measures relative brightness by a series of filters....
Cool star emits more green photons; Hot star emits more UV and violet photons. |
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color lies
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If there is a lot of dust between the star and us, the star will appear redder in color than it
actually is. |
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spectral classification of stars
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obafgkm (+like that 4 brown dwarfs)
hot 2 cool, type and # of absorption lines change |
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balmer absorption line
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electron absorbs a photon of the correct quantized energy and jumps from the n=2 level to a higher level
|
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brown dwarfs
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failed stars;
to small; glow because of kevin-hemholtz contraction; peak wavelength in infared |
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determining the radii of stars1
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measure stellar diameter
not very effective |
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radii of stars 2
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interferometers 2 combine light from tons of telescopes to make higher res,
|
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radii of stars 3
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ellipse by moon
5% of stars |
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radii of stars 4
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stephen's law:
(Energy Flux=F = (o w tail)*T^4 Luminosity of a Star (L): L =4pi R^2 x(o w tail)*T^4 |
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stellar radii
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factor of 60,000
sun is med-low giants, super, dwarfs |
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Hertzsprung-russell diagram
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luminosity l
l ________ surface temp. * main sequence stars |
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luminosity class
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The width of spectral lines
can be used to define luminosity classes * mass and age |
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spectroscopic parallax
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find distance;
find mag and class; use spectral line 2 find lum. use inverse square * can see several thousand parsecs |
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stellar masses
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binary pairs;
visual binaries; spectroscopic binaries; eclipsing |
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visual binaries
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keplers 3 law
most accurate for finding masses |
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radius
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depends on mass
|
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star life age
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Stars more massive than the Sun live much shorter lives.
Stars less than the Sun live much longer lives. |
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reflection nebulae
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The bluish haze is
evidence of dust in the cloud....Starlight is scattered and reflected by these small grains... The grain size ~500 nm...i.e equal to wavelength of visible light... Scatter blue more efficiently than red |
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dark clouds
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very cold
T = 10 - 100 K Temperature low enough for hydrogen to form molecules 10^4 -10^9 particles/cm3 (atoms, molecules & dust) Compared to <HII> gas ~ 10 3 atom/cm3 ; density air in this room ~10^19 atoms/cm3) |
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dust clouds
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makes stars appear redder
NOT a Doppler shift |
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dust is a catalyst
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1. molecules form on surface
2. shield 3. coolant |
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star formation
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Star formation happens when part of a dust
cloud begins to contract under its own gravitational force; as it collapses, the center becomes hotter and hotter until nuclear fusion begins in the core. |