October 31, 2011 – 10am class

1. October 31, 2011 – 10am class Review Session: Sunday, Nov. 6, here, 6-8pm Midterm #2: Nov. 9 Citizen Astronomy Projects now on d2l

2. Stellar Lifetimes on the Main Sequence: More Massive Stars are more luminous, and are burning hydrogen more efficiently. They therefore have shorter lifetimes on the Main Sequence before they burn up the Hydrogen in their core Shine bright, die young

3. After the hydrogen fuel in the core of the main sequence star is used up, There is no longer enough thermal pressure in the core to balance gravitational collapse. No more hydrostatic equilibrium What happens next? Star rearranges itself outer layers expand and cool Star becomes a red giant or supergiant Eventually more processes happen and the red giant becomes a supernova or planetary nebula, and then a white Dwarf, neutron star or black hole – more on this later

4. STAR CLUSTERS All the stars in a cluster are (1) at the same distance, and (2) were formed together, so are the same age. Open Clusters: Young (Less than a billion years old) found in the disk of the Milky Way typically 100's - 1000's of stars often have gas and dust Globular Clusters: Contain oldest stars in the Milky Way -- 12-13 billion years old stars in orbit around center of cluster, gravitationally bound Typically 100,000 - million stars never have gas and dust

5. PLEIADES Open Cluster

6. H & Chi Persei, a Double OPEN Cluster

7. The Jewel Box: 10 million years old

8. M46 and M47: Open Clusters

9. Charles Messier (1730-1817) French Astronomer Made a catalog of 103 “nebulous” i.e. fuzzy objects Nebula = cloud Purpose: help comet hunters M47 = 47th object on Messier’s list Some are clusters of stars, some are galaxies, some are gas clouds

10. M55: Globular Cluster

11. Omega Cen: Globular Cluster

12. M80: Globular Cluster

13. Schematic of Milky Way Galaxy Open clusters: In the Disk only

14. H-R Diagram Hertzsprung- Russell Diagram Plot Luminosity versus Surface Temperature (or equivalently, Luminosity versus spectral classification)

15. Ages of Star Clusters and the HR Diagram In Old clusters, some of the stars have "left" the Main Sequence – and become Red Giants, white dwarfs, etc. The age of the cluster = the lifetime of the stars at the "main sequence turnoff" in the H-R diagram.

18. Step 1: Find the Turn-off MASS, ignore “Blue Stragglers” Step 2: Use the plot on the right to figure out the main sequence lifetime (GYRS) Of the Turn-off Mass star. This is the age of the cluster.

19. Pulsating Variable Stars: Cepheid Variables, RR Lyrae

20. Pulsating Stars

22. Period of pulsation is correlated with absolute magnitude. Thus, given the apparent magnitude and period of pulsation, you can derive the DISTANCE to the star.

23. Midterm #2 covers through here

24. STAR-FORMATION Key Concepts: * Stars form by the gravitational collapse of dense clumps of interstellar gas, molecules and dust. * The collapsing protostar forms a disk and jet. * The collapse stops when nuclear fusion begins in the protostar core. * When a giant molecular cloud of interstellar gas forms stars it fragments into several protostars, and eventually a cluster of stars forms. * If the clump is too massive it splits into a binary star system. * Eventually the protostellar disk turns into a system of planets orbiting the star.

25. Schematic of Star-Formation

27. A real protostellar disk and jet, with dark dust lane running through the disk:

28. Two important physical principleswhich govern what happens when gas clouds collapse to form stars • ADIABATIC Contraction and Expansion • (no source or sink of energy) • Gas contracts  HEATS up • Gas expands  COOLS • CONSERVATION OF ANGULAR MOMENTUM • When gas cloud collapses, conservation of angular • momentum makes the cloud spin faster and faster in one • plane, and collapse in the other dimensions

30. Images of Star-Formation in the Milky Way Galaxy

31. Bow shock by a young stellar object in Orion

33. Disk in Orion