6_-_HR_Diagram - 6 Hertzsprung-Russell Diagram The Plan Are all stars the same Why are some hotter and others cooler What about luminosity These and

6 – Hertzsprung-Russell Diagram Hertzsprung Russell 2 The Plan • Are all stars the same? • Why are some hotter and others cooler? • What about luminosity? • These and other issues are resolved by the Hertzsprung-Russell Diagram – Main Sequence – Luminosity Function – MS stars sit on the HR diagram 10 9 yr – Giants move over periods of 10 5 yr – White dwarf move over 10 10 yr 3 Sun Degenerate gas pressure Homogeneous Inhomogeneous M < 0.08Mo will not burn H M>50Mo will be unstable O B A F G K M HR Diagram 4 re: HR Diagram • The range in Luminosity, 10 8 :1! (It’s even up to 10 14 :1 if you count the brown dwarfs!!) – Max 10,000 L Sun O5 stars – Min 0.0001 L Sun M5 stars • What is the range in Temperature, 15:1 – Max 40,000K – Min 2,500K • What are R max and R min ? • L α R 2 x T 4 => R α L 1/2 T -2