19-1 How a main-sequence star changes as it converts hydrogen to helium 19-2 What happens to a star when it runs out of hydrogen fuel 19-3 How aging stars can initiate a second stage of thermonuclear fusion 19-4 How H-R diagrams for star clusters reveal the later stages in the evolution of stars 19-5 The two kinds of stellar populations and their significance Chapter 19 By reading this chapter, you will learn 19-6 Why some aging stars pulsate and vary in luminosity 19-7 How stars in a binary system can evolve very differently from single, isolated stars

Red Giants

The lives of the sun 1.Explain what will happen to the sun in the future. (a- the sun will be stable for another few billion years, b- sun will gradually get larger and will become a red giant, c- sun have started its He fusion already, d- sun will start the new set of fusion after it expand. 2.T/F: Larger star will have more mass to burn, so it will last for a long time. 3.During the first red giant stage: a- shell hydrogen fusion is common, b- shell helium fusion is common, c- Fe fusion at core is common, d- Helium fission is common Click on “enter” to review your answers: 1. a,b,&d, 2. F, 3. a

Post main sequence stars

cluster’s age

Variable stars

Cepheid variable Its change in apparent magnitude match the expansion and contract of the star surface.

To review the lives of the stars, work on the Stellar Evolution worksheet (part of your homework this week!) The letters A-F represent stars 1.This diagram is a plot of temperature vs. luminosity. What do we call this diagram? 2.Which two stars have same temperature? 3.Do these pair(s) of stars have same stellar classification? explain 4.Which two stars have same luminosity? 5.Do these pair(s) have same stellar classifications? explain 6.Which letter is most similar to the current sun’s location n the diagram? 7.When the sun starts to die, the sun will start to expand. The sun will be larger, hence brighter, but it till be lower temperature. Which letter represents this state of the sun? What do call this type of star? 8.After the dieing process the sun starts, sun will be variable star for short period of time. The sun will change its luminosity as series of shell fusion takes place. Which letter represents this state of the sun? What do call this type of star? 9.When the sun completely die, the sun will have exposed core, hence the temperature will be higher, but it sill be very small (about size of the earth) so it will not emit as much light. Which letter represents this state of the sun? What do call this type of star? 10.Which letters are in its hydrostatic equilibrium or main sequence? 11.Which of the main sequence stars have longer life expectancy? Why? Lum (L sun ) Temperature A E D C B

Mid life crisis of the stars! 1.As the star starts to die, it starts to pulsate. This happens when the star is in: a- main sequence, b- instability strip, c- white dwarf stage, d- this could happen at any place on HR diagram 2.To determine the age of relatively old star cluster, you would look for: a- by counting the number of stars., b- Largest main sequence star, c- by finding variable stars, d- smallest star in the main sequence. 3.Which type of variable star is brighter for its mass? a- Lyra variable, b- metal poor Cepheid variable, c- metal rich Cepheid variable, d- the stars still in main sequence

Close binary star systems Mass transfer in a close binary system occurs when one star in a close binary overflows its Roche lobe Detached binary Semi- detached binary Contact binary Over contact binary

The other type of varying brightness: binary system 1.How close the binary stars needs to be for any type of mass transfer to take place? A- detached, b-semi-detached, c- contact, d- over contact. 2.In Which type of binary the atmospheric composition will be identical. A- detached, b- semi-detached, c- contact, d- over contact. 3.T / F: the initial mass of the star is the only condition that determines how long the star will live.