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Announcements: -Public Viewing postponed to THIS Friday Evergreen Valley College

Announcements: -Public Viewing postponed to THIS Friday Evergreen Valley College http://www.evc.edu 7PM-10:30 check website for weather information maps available online Pick up copy of handout: required for credit!! Homework #9 due Thursday Exam #3: May 3.

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Announcements: -Public Viewing postponed to THIS Friday Evergreen Valley College

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  1. Announcements: -Public Viewing postponed to THIS Friday Evergreen Valley College http://www.evc.edu 7PM-10:30 check website for weather information maps available online Pick up copy of handout: required for credit!! Homework #9 due Thursday Exam #3: May 3

  2. An actual HR Diagram 5,000 stars with most accurate distances measured by Hipparcos. 85% lie on Main Sequence.

  3. Relative Sizes Antares: M1I Betelgeuse: M2I Aldebaran: K5III Rigel B8I Arcturus: KII Pollux: K0III

  4. The cone shaped object is a) Cold dust and gas obscuring radiation b) Bi-polar jet What causes the red color? a) Hydrogen emission b) Hydrogen absorption c) Doppler shifted radiation

  5. Chapter 13

  6. Introduction • Where do stars come from? • Giant Molecular Clouds • Bok Globules • Interstellar Medium (ISM) • Protostars • Pre-Main Sequence Stars • How do they age (evolve) • What is their fate?

  7. Where do Stars Come From?

  8. Giant Molecular Cloud breaks up into smaller clumps that collapse under their own gravity. • Rotation becomes more and more important as clump contracts. • Disk forms • Bi-polar jets are created; Cloud clears away

  9. Bipolar Flows, Jets, and Herbig-Haro Objects

  10. Bipolar Flows Easily Seen at Radio Wavelengths Radio Image redshifted blueshifted

  11. The nebulae around protostars are shaped into disks because of the same process that causes dough to become flat when it is a) spun in the air like pizza dough b) rolled with a pin like pizza dough c) squashed between plates like dough for a burrito d) baked on a flat sheet like a cookie.

  12. The factors that tend to work against collapse are • I. The magnetic field of the cloud • II. The presence of a supernova nearby • III. The existence of molecules in the gas • IV. Heat in the gas • V. rotation of the cloud • I, III, V • I, IV, V • II, III, V • II, IV, V • III, IV, V

  13. When will a protostar become an official star? Protostar continues to collapse, becoming denser and hotter in its interior. Once temperatures reach about 7 million Kelvin, hydrogen fusion reactions begin to take place. Protostar becomes a star when fusion begins. Process (protostar to star) takes about 1-100 million years.

  14. Protostars in the HR Diagram NGC 2264: a young cluster of stars (10 million years old) Note the large amount of gas/dust left over from star formation.

  15. Protostars in the HR Diagram High-mass stars collapse faster than low-mass stars. (larger gravitational forces are involved). The faster they collapse, the sooner core temperatures sufficient for hydrogen fusion are reached.

  16. Stellar Mass Limits M < 0.08 solar masses: Not hot enough for fusion Brown Dwarfs (failed star) M > 100 solar masses Not observed extreme temperatures/luminosity radiation pressure

  17. A Star’s Mass Determines its Core Temperature Hydrostatic Equilibrium: gas pressure balances gravity higher gravity, higher internal pressure, higher internal temperature!

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