Question 15:Analyze the observations for each of the other four variable stars in this field. You should determine the period, light curve amplitude, and the type of variable. You should clearly discuss what factors led you to classify the variable star in the manner you did (which may involve a process of elimination]

Which of the following can you determine about a star without knowing its distance, and which can you not determine: radial velocity, temperature, apparent brightness, or luminosity? Explain.

Review this spectral data for five stars. Which is the hottest? Coolest? Most luminous? Least luminous? In each case, give your reasoning.

We can estimate the masses of most of the stars in Appendix J from the mass-luminosity relationship in Figure 18.9. However, remember this relationship works only for main sequence stars. Determine which of the first 10 stars in Appendix J are main sequence stars. Use one of the figures in this chapter. Make a table of stars’ masses. Figure 18.9 Mass-Luminosity Relation. The plotted points show the masses and luminosities of stars. The three points lying below the sequence of points are all white dwarf stars.

Look at the list of the nearest stars in Appendix I. Would you expect any of these to become supernovae? Why or why not?

If two stars differ by 8.6 magnitudes, what is their flux ration?

Explain how parallax measurements can be used to determine distances to stars. Why can we not make accurate measurements of parallax beyond a certain distance?

The eclipsing binary Algol drops from maximum to minimum brightness in about 4 hours, remains at minimum brightness for 20 minutes, and then takes another 4 hours to return to maximum brightness. Assume that we view this system exactly edge-on, so that one star crosses directly in front of the other. Is one star much larger than the other, or are they fairly similar in size? (Hint: Refer to the diagrams of eclipsing binary light curves.)

Figure 18.7 shows the velocity of two stars in a spectroscopic binary system. Which star is the most massive? Explain your reasoning. A plot showing how the velocities of the stars change with time is called a radial velocity curve; the curve for the binary system in Figure 18.6 is shown in Figure 18.7. Figure 18.7 Radial Velocities in a Spectroscopic Binary System. These curves plot the radial velocities of two stars in a spectroscopic binary system, showing how the stars alternately approach and recede from Earth. Note that positive velocity means the star is moving away from us relative to the center of mass of the system, which in this case is 40 kilometers per second. Negative velocity means the star is moving toward us relative to the center of mass. The positions on the curve corresponding to the illustrations in Figure 18.6 are marked with the diagram number (14).

Which method would you use to obtain the distance to each of the following? A. An asteroid crossing Earth’s orbit B. A star astronomers believe to be no more than 50 light-years from the Sun C. A tight group of stars in the Milky Way Galaxy that includes a significant number of variable stars D. A star that is not variable but for which you can obtain a clearly defined spectrum