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Special Stars
Take-Away Points
• Variable Stars• Multiple Stars
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
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
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
Dusty Stars
• R Coronae Borealis • Mostly Constant Brightness• Occasionally Dim Dramatically• Cause: Carbon Dust Formation
Catastrophic Variables
• Flare Stars (Red Dwarfs)• Novae• Supernovae
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
Hubble Image of
Sirius
Orbit of Sirius B
Double Star
Triple Star
Lyra
Lyra
Epsilon Lyrae
The Trapezium in Orion