Chapter 13: Stellar Evolution

1.

Calculate the main-sequence lifetime of the Sun by first determining the rate at which it burns hydrogen (refer to chapter 11) and then dividing that rate into its core mass. If your answer is in seconds, convert to years given that there are about 3.2 3 107 seconds in a year.

2.

Calculate the escape velocity from a red giant’s atmosphere (use the formula for escape velocity from chapter 2). Assume that the star’s mass is 1 M( and its radius is 100 R( How does this compare with the speed at which a planetary nebula shell is ejected?

3.

How long will it take a planetary nebula shell moving at 20 kilometers per second to expand to a radius of one-fourth of a light year?

4.

Figure 13.25 (right) shows the H-R diagram of a star cluster. How old is it?

5.

Calculate the average density of a red giant star in grams per cubic centimeter. Take the star’s mass to be 2 x 10³³ gm and its radius to be 3 x 10¹² cm. How does this density compare with that of the air we breathe (about 10³ gm/cm^-3)