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Hertzsprung Russell (HR) Diagram Spectral Types: Proxy for T eff Or surface temperature

Hertzsprung Russell (HR) Diagram Spectral Types: Proxy for T eff Or surface temperature. Our Sun: 5,700 deg Kelvin Or about 10,000 F. O B A F G K M L T. Not to scale: Red Giant 100 times bigger than Main Sequence Star. Pre main sequence evolution: Protostellar, self-gravitating

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Hertzsprung Russell (HR) Diagram Spectral Types: Proxy for T eff Or surface temperature

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  1. Hertzsprung Russell (HR) Diagram Spectral Types: Proxy for Teff Or surface temperature Our Sun: 5,700 deg Kelvin Or about 10,000 F O B A F G K M L T

  2. Not to scale: Red Giant 100 times bigger than Main Sequence Star

  3. Pre main sequence evolution: Protostellar, self-gravitating Gas cloud collapses Then contracts in Hydrostatic equilibrium Develops hot radiative core Reaches ignition point for Hydrogen burning Virial theorem: as cloud shrinks Gravitational energy is released Half of it goes into heating the interior Half of it is radiated away as luminosity (and its more luminous than it will be When hydrogen is burning)

  4. 3) Start of main sequence (hydrogen burning) 4) End of main sequence (core is now all helium) 5) Climbing giant branch hydrogen burning in shell around inert helium core hydrogen envelope swells up 6) Helium ignition in a “flash” 7) Helium burning to carbon/oxygen

  5. 7) Second climb up Giant brach: H- and He-shell burning Around inert C/O core (the pre white dwarf) 8) Ejection of Planetary Nebula exposes core Which contracts and Gets very hot as Upper layers peeled off Enters white dwarf phase Near 100,000 deg Kelvin 9) White dwarf phase: Just cooling off and Getting dimmer

  6. The Ring Nebula in Lyra The pre-white dwarf is the very blue star at the center !

  7. A Planetary Nebula Star ejects envelope of unburnt hydrogen Many cool pics On Hubble web site

  8. Sirius AB -- a Visual Binary 60 arcseconds = 1 arcminute = 1/60 of a degree

  9. The Globular Cluster Messier 5 Stages of Stellar Evolution: A) Core hydrogen burning = main sequence H > He when finished: helium core B) Red giant branch = hydrogen burning in shell around helium core C) Tip of giant branch = ignite helium core D) Core burns He > C, O E) He shell burning ejection of planetary nebula F) Becomes white dwarf

  10. Open / Galactic Star Cluster NGC6791 -- 8 Billion Years, 2-3 x solar metals Isochrones for 7, 8, 9 Gyr

  11. Massive star evolution (> 8-10 M) After helium burning To C,O C ignites to O, Ne, Mg Ignites to Si, S Si, S to Fe peak elements (Ni, Ti, lots of Fe) Now stellar core can do no more burning to produce energy So it collapses and Explodes as a Supernova Remnant core: Neutron Star or Black Hole

  12. Supernova in 1054 A.D. Recorded by the Chinese The Crab Nebula Pulsar inside! Pulses every 1/30 second

  13. Pulsar: Rotating, Highly magnetic Neutron star Like a rapidly spinning Searchlight beam!

  14. An X-ray pulsar (also optical, radio)

  15. Jocelyn Bell Burnell British radio astronomer Graduate student in 60s Discovered first pulsars In radio signals With advisor Anthony Hewish Sir Anthony Hewish Nobel prize in physics 1974 for pulsars

  16. Problems • Impostors: contamination by other small stellar and substellar objects: the radii of small stars, brown dwarfs and giant planets are similar SM T HJ J

  17. Burrows and Liebert 1993 Reviews of Modern Physics

  18. A new class of planets • OGLE planets have shorter periods than RV planets. • Transit searches find a different population because the selection effects are different. Fig. From the California-Carnegie team

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