special stars. take-away points variable stars multiple stars

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

Eta Carinae

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