1. Special Stars

2. Take-Away Points Variable Stars Multiple Stars

3. Variable Stars How Identified – R through Z (T Tauri) – RR – ZZ, SS-SZ, etc. (RR Lyrae) – AA-AZ, BB-BZ, etc. (FU Orionis) – V + number (V1234 Sagitarii) Extrinsic: Variation not due to internal processes Intrinsic: Variation due to internal processes

4. Extrinsic Variables Eclipsing Binaries Rotating Variables – Ellipsoidal: Close binaries distorted by tidal forces. Cross-section varies as they rotate – Starspots: Stars have large brighter and dimmer areas

5. Intrinsic Variables Cepheids and Related Types – Stars Pulsate As Star expands, its outer layers cool Electrons combine with He atoms Outer layers become more transparent Star brightens Easier escape of radiation allows star to contract Long Period Variables – Red Giants and Supergiants – Pulsations controlled by ionization of H

6. Dusty Stars R Coronae Borealis Mostly Constant Brightness Occasionally Dim Dramatically Cause: Carbon Dust Formation

7. Catastrophic Variables Flare Stars (Red Dwarfs) Novae Supernovae

8. Eta Carinae

9. Binary Stars About 5% of Stars are multiple Contact Binaries – Almost always eclipsing variables Spectroscopic Binaries Visual Double Stars Hierarchical Multiple Stars Trapezia: Still Evolving Optical Doubles: Chance Alignment

10. Hubble Image of Sirius

11. Orbit of Sirius B

12. Double Star

13. Triple Star

14. Lyra

16. Epsilon Lyrae

17. The Trapezium in Orion