October 28, 2011 – 10am Class

1. October 28, 2011 – 10am Class On-line Quiz 9 due next Fri, Nov. 4 Midterm #2 Wed Nov. 9 Section 2 Star parties: please tell us if you do not need a ride! Citizen Astronomy Labs: Due last day of class. Posted on d2l this weekend. All students: Read Introduction, do Galaxy Zoo, and #1 OR #2. Kepler Extra solar planet search Kuiper Belt Object search Galaxy zoo Section 3 students who are not going to Mt. Lemmon: Do all three assignments Cryptobiosis: tardigrades at Saguaro National Monument

2. STARS -- continued What is a star? Why do they shine? How old are they?

3. Stellar Masses Stellar masses are measured by observing binary stars, and using Kepler's 3rd Law to determine the mass of the stars from the period of their orbit. Types of Binary Stars: * Visual Binaries -- direct image shows two stars orbiting each other * Spectroscopic Binaries – two stars are too close to see as separate stars, but spectrum shows absorption lines from two stars with variable Doppler shifts. * Eclipsing Binaries -- one star disappears when it passes behind the other

4. Visual Binaries:

5. Artist’s conception of a visual binary

6. Eclipsing Binaries:

9. Spectroscopic Binaries:

11. Most massive stars: 100MSun Least massive stars: 0.08MSun (MSun is the mass of the Sun.)

12. Summary of Stellar Properties: Also there are Giants, Supergiants and white dwarfs: Same Temperature as stars in the table, but different luminosity and radii.

13. B star is much larger, brighter and hotter than the Sun. An example is HD93129A shown below:

14. The Hertzsprung-Russell Diagram • When you plot LUMINOSITY versus Temperature for stars in the sky, the result is not a scatter plot • Hertzsprung and Russell first realized this, and the diagram they made is still an important tool in astronomy for understanding stars

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

17. Main Sequence: Stars fusing hydrogen to helium Example: The Sun

18. Giants are more luminous than a main sequence star of the same temperature. Giants tend to be relatively cool (T < 6000 Kelvin) but luminous (L = 100 to 1000 Lsun). Supergiants are even more luminous than giants. Supergiants can have any temperature, but they are always VERY luminous, with L = 100,000 to 1,000,000 Lsun. White Dwarfs are less luminous than a main sequence star of the same temperature. They are called WHITE dwarfs because they are fairly hot; white-hot, in fact, with temperatures of T > 5000 Kelvin. The are low in luminosity, with L = 0.0001 to 0.01 Lsun.

19. In a sample of 1,000,000 stars from the Milky Way, • on average you'd find: • 900,000 main sequence stars • 96,000 white dwarfs • 4000 giants • 1 supergiant

20. So now we have a range of stellar colors and sizes. For example, Aldebaran is a red supergiant star:

21. Arcturus is an orange giant star:

22. Betelgeuse A very large red giant in Orion

23. White Dwarfs: about the size of the Earth