Pathways to Astronomy

Stephen E. Schneider

Chapter 63 Variable Stars - all with Video Answers

Educators

Chapter Questions

Problem 1

An interferometer measured the change in radius of one Cepheid as about $10 \%$ during its 10 -day period. The star was measured to have an average radius of 40 million $\mathrm{km} .$ How fast was the surface of the star moving outward, on average, if it took 5 days to expand by $10 \%$ ?

Susan Hallstrom

Numerade Educator

02:41

Problem 2

The same interferometer as in problem 1 measured the change in radius of an RR Lyrae star to be $10 \%$ during its 10 -hour period. If the star was measured to have a radius of 10 million $\mathrm{km}$ and took half a period to expand by this amount, what would be the speed of the surface of the star as it expands?

Prabhu Ramji

Numerade Educator

01:02

Problem 3

A variable star varies in luminosity and temperature throughout its cycle according to the values listed in Table 63.1 . The phase indicates the fraction of time between one maximum and the next. Graph the luminosity and temperature change, then plot the positions of the star in the H-R diagram. Connect the sequential points with a line to show the pattern of variation.

Clarissa Noh

Numerade Educator

00:57

Problem 4

Using the information from Table 63.1 , calculate the average luminosity of the variable star at the four distinct phases listed (the phase listed as 1.00 is back around to the same phase as 0.00 ). Using your average luminosity, estimate the period this variable should have if it is a Cepheid from Figure 63.5.

Farhanul Hasan

Numerade Educator

01:49

Problem 5

Use the information from Table 63.1 along with the StefanBoltzmann law to calculate the radius of the variable star at each phase. When is the star largest? When is it smallest?

Farhanul Hasan

Numerade Educator

00:57

Problem 6

Suppose a Cepheid has a period of 5 days. Estimate its luminosity from Figure $63.5,$ then determine its distance if its measured brightness is $4 \times 10^{-12}$ watts/m $^{2}$.

Farhanul Hasan

Numerade Educator