AST MARCH 26.docx

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30 Mar 2012
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AST251 MARCH 26, 2012
LECTURE 11
INTRO
- DEPEND ON WHAT WE CAN SEE, WHAT WE SEE NOT BE REP OF ENTIRE PPLANETS THIS CALLED
SELECTION BIAS
Main sequ
- Most of time on main sequence
- Burn h in he ,
- Main sequence all related mass, surface temp, lum and shorter the lifetime,
- More fuel to burn live shorter
- G is the sun,
- Bottom 3 low lumoinoaity cool stars
- Top 3 high lum hot stars .1 percent or million times more luminous then the sun
Properties
- Life time Is op big stars die quicly very small stars live almost forevcer 100s of billions of years
- Ob die to quick, life on earth 100 my to develop
- 3 percent on a and f
- So low mass region long life times many stars in these categories, sun is a g star know one planet
around g star
Stars cooler
- Luminosity temp goes down
- Bottom line is less lum stars habitable zone closer to the sun, such to support liquid water
- Earth quite in inner edge of habitable zone, venus and mercry in and mars on outer this is g
- Fir k mercury good
- For m mercury would be too far away
- Mmons of Jupiter show same face tidal locking, closer planet is to star more likely tidally locked
on side always faces star another doesn’t, whether good for life or not is unknown
Much cooler
- Lower mass, brown dwardfs, so small not heat up in center to start nuclear burning, just h balls
larger versions of Jupiter circles brown dwarfs below .08 solar masses no chance for life
Lower surface temp less lum
Binary stars
- Sun exceptional is that its alone,
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- Most stars come in pairs one star and another
- Both stars orbit common center fo mass elipses
- 60 percent of stars do this,
- Images of them Sirius brightes star in sky has companion star orbis around it, but exhausted all
senergy and is white dwarf origninally more mass but dies quicker
Eclipsing
- system edge on, on passes front then behind,
- in front blocks some light from behind so total lum goes down alittle and then back up and
behind drops light variation another way to find if two close to sepearte with telescopes
- that is how we know
- so close outer layers tocuh each other
planets and them
- knowpolanets orbits
- systems of 3 bodies unstable 2 bodies close and 3rd body far like tatoine
- or planet orbits one star and other is far away
- if same separation It is unstable and planet kicked out within short number f orbits
- know 3 systems planet size of Saturn orbiting binary star
- finding in binary harder then 1 bc take into account motion both stars and one planet
- orbit planet unstable
- so focus on indi stars
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