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
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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
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R Coronae Borealis
Mostly Constant Brightness
Occasionally Dim Dramatically
Cause: Carbon Dust Formation
Catastrophic Variables
• Flare Stars (Red Dwarfs)
• Novae
• Supernovae
Eta
Carinae
Binary Stars
• About 5% of Stars are multiple
• Contact Binaries
– Almost always eclipsing variables
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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