Stellar Evolution Life Cycle of Stars

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Stellar EvolutionLife Cycle of Stars
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Star Properties

• Representative versus Prominent Stars
• HR diagram and main sequence
• Russell-Vogt Theorem
• Non-Main Sequence Stars
• High luminosity K and M stars Red Giants
• Super Giants
• Low luminosity A, F, and G stars White Dwarfs

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Luminosity Classes

• Higher luminosity stars less dense thinner
  spectral lines
• Luminosity Classes
• I gt Super Giants
• II gt Bright Giants
• III gt Giants
• IV gt Sub Giants
• V gt Main Sequence

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Relationships

• Mass Luminosity
• Main Sequence more mass higher luminosity
• L 8 M3.5
• Luminosity Radius
• Main Sequence larger size greater luminosity
• Luminosity Temperature
• Main Sequence higher temperature greater
  luminosity
• Hydrogen Burning Lifetime
• ? M/L x (9 billion years)

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Stellar Evolution

• Evidence that Stars Continue to Form
• Large MS stars short lifetime
• 20 M?s 100 million years
• Star clusters with large MS stars must be young
• Sun is 5 billion years old universe 10 13
  billion
• Open Clusters drift apart with time yet we see
  these clusters, i.e. they formed recently

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Protostar (1)

• Stellar nebula
• Cloud of gas (and dust) from which star forms
• Compositon
• Mostly hydrogen, some helium
• Other components (figure 18-1)
• CO2, H2O, H2CO, C2H5OH, etc.
• Temperature 10 to 20 K
• Density 1 molecule per cm3

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Density Comparisons

• Iron (solid) per cm3
• Water (liquid) per cm3
• Air (gas) 2 x 1019 per cm3
• Interplanetary Space per cm3
• Molecular Nebula 1 per cm3

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Gravitation Collapse

• Molecular Cloud
• Turbulence likely to start gravitation collapse
• Density increases pocket of greater density
  mass
• Gravitational attraction draws mass together
• Energy of Molecules Increases
• Conversion of gravitational energy to kinetic
  energy
• Gravitational force accelerates molecules
• Increase in velocity increases in temperature
• Increase in density

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Change of Cloud Properties

• Change is size
• Molecular cloud ? 100 AU
• Radius of Star 0.2 10 Rs (0.001 0.05 AU)
• Change in Temperature
• Molecular Cloud 10 20 K
• Star 2500 40,000 K surface
• 15 to 100 x 106 K core
• Temperature increase ? 1/r
• Density ( mass/volume)
• Density ? 1/r3

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Competition of Gravity and Pressure

• Gravitational force
• Mass and size
• Conversion of Gravitational to Kinetic Energy
• Pressure
• Temperature and density
• Jeans Size or Mass
• MJ 1036 kg ( 109 Ms)

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Mass Limits for Star Formation

• Most Stars from 0.2 to 20 Ms
• Lower mass limit is 0.08 Ms (Jupiter is 0.016)
• Upper limit is 150 Ms
• Eta Carina estimated 100 150 Ms

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Protostar Formation

• Rotation and disk formation
• Development of high temperature in core
• Core Temperature reaches 106 K
• Deuterium burning
• T-Tauri Stars
• Protostar Phase for between 106 to 108 years
  depending on mass (high to low)

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Protostar Formation (2)

• Core Temperature reaches 106 K
• Deuterium burning
• Bipolar jets of gas
• Disk accretion of material
• T-Tauri stars
• Herbig Haro Objects
• Protostar Phase for between 106 to 108 years
  depending on mass (high to low)

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Protostar (3)

• High speed episodic stellar winds remove excess
  gas
• Bok Gloubues
• Herbig-Haro Objects
• High mass stars and their winds may inhibit
  formation of small mass stars

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T-Tauri Stars

• Protostars evolving to Main Sequence Status
• Low mass 02. to 2 Ms, spectral types F to M
• Extensive convection zone and strong magnetic
  activity
• Found close to or within dusty clouds
• Fluctuations in brightness
• Bipolar jets
• Accretion from Disk

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Thermonuclear Energy Production in Stars