Stars III. Stellar Evolution

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StarsIII. Stellar Evolution
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????

• ?????????????????????????,???????????
• Sections 4.2.1, 4.2.2,4.2.3 (?????????????Chandra
  ????),
• 4.4.2(???????????), 4.4.3,4.5(???????)

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Three kinds of timescales

• The nuclear timescale
• how long it takes the reservoir of nuclear
  energy in the star to be released. (see last
  section) main sequence
• Kelvin-Helmholtz timescale (or thermal timescale)
• how long it takes for thermal energy produced
  in the center of the star to work its way out via
  energy transport or how long the energy release
  lasts from gravitational contraction. (see last
  section)
• The free-fall timescale (or dynamical timescale)
• how quickly the star mechanically adjusts to
  changes.

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In units of 106 years
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Free-fall timescale
Maoz p.32
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Post-MS evolution
The formation and subsequent collapse of
condensations in the ISM, the contraction of
protostars towards the MS will be discussed in
Section IV.
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Evolutionary paths in the HRD up to the point
where He burning sets in. The shade of the line
segments indicates the time spent in the
corresponding phases. MS (1-3)
life-times 1.0MT 9.0E9 yrs 2.2MT 5.0E8
yrs 15MT 1E7 yrs GB (5-6) life-times 1.0MT
1.0E9 yrs 2.2MT 3.8E7 yrs 15MT 1.5E6 yrs
(6-10)
Iben 1967, ARAA
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Schematically Overview
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(No Transcript)
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The evolutionary end points of stars with
differentmasses shown as a function of central
density
BH
?????
?????
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Red giant phase
?????,???????????,???????????,??????????(pp?CNO),
??????????????,?????,??????????????????????????Ha
yashi??????
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Horizontal branch
He??
????, He????,He??????????????? ???,He???,He
flash, 40???????,????????????????????????????,???
,???,????,???runaway.
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AGB (asymptotic giant branch ) phase
???He?????,??C-O?,???He?????H????,
C-O???????,????,????,????,??????,??????
Hayashi??????, ?????????????????,????????,???????,
?????????
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????????

• gt10M????????
• ???Fe??,???????,???????
• ?????Eddington??,??????????????HR?????????,???????
  ??,???????,??????,???,????????????,???,????
• ????????,?????????????????????,??????????????

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??????????????????C??,??He??. ???C?????,O??,C????,
He?????? ????????
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?????????1)?????,2)???????????
??Fe???,????????,??????,????,?Fe?????Chandrasehkar
??(1.46M)?,????
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???????????Maoz p.83 a. ????????(neutronization)
b. ??????????,?????????,Fe???????(photodisintegra
tion)? ????????, , ??????????,????????????,??
???????????,??,??????,???????????????????????????
1015g cm-3? ?????????????????????
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?????????????????????????,
???????
??????????
?????????????????????(???????????1057?,??30MeV),?
?????????,??????????
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????????
????
SN 1987A???????????,20????30MeV
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A note ????
Maoz, p.97

• ??????????(??)
• ???????????

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stellar evolution Summary
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Homework Textbook of D. Maoz, P.108, 1, 9,10