1) An H-R diagram has been draw below with grid-lines for reference. Answer the following questions about this diagram, no explanations needed (but for possible partial credit in case of a wrong answer, you are encouraged to show all work).

a) (4 pts) Is star B larger in size, the same size or smaller than our Sun?

c) (4 pts) Draw in with an ³X² the location of a star with a surface temperature of 12,000K and a radius one-fourth the radius of the Sun.

2) Suppose we create a stellar catalog that consists of all stars in the sky for which we are able to measure an accurate parallax angle (about 1,000 stars). Will this catalog be a representative sample of the 100 billion stars in the Milky Way Galaxy? Explain.

3) Below are the light curves for two eclipsing binary systems:

Assume for this question that the companion stars in both systems have been verified via Doppler shifts to have identical orbital velocities around their parent stars.

a) (7 pts) Which system's companion star has a larger orbital distance? (left, right) Justify your answer.

b) (7 pts) Which system's parent star is more massive? Justify your answer (either mathematically or in words).

4) Suppose we are using Doppler shift measurements to estimate the orbital velocity of the companion star in a binary system. Weıve used the angular size of the orbit and the (known) distance to the system to deduce the orbital distance between the central star and the companion star. We assume that the system is being seen edge-on and calculate the mass of the central star based on our estimates of the orbital velocity and orbital distance. The system is *not* being seen edge-on, however. It is tilted about 30 degrees away from being edge-on. Will this estimate of the central starıs mass be greater than, less than or about equal to the true mass of the central star? Explain your answer.

5) Suppose star X has a mass about equal to one-third the mass of our Sun.

a) (8 pts) State explicitly how the absolute luminosity of star X and the expected main sequence lifetime of star X will compare to the Sun. Show your work.

b) (6 pts) If star X were much less massive, say only one-twentieth (5%) the mass of the Sun, it is likely that it wouldnıt even be considered a star at all. Explain why this is true (as part of your answer, explain why there is a minimum mass for stars).

6) Name and explain two reasons why the core of the Sun is slowly increasing in size over the course of its main sequence lifetime (the Hydrogen-burning phase).

7) Below is the spectrum of a star as viewed through two separate interstellar clouds, both along the line of sight to the star. The two clouds have the same composition, but different temperatures. For reference, the blue and red ends of the spectrum have been noted.

a) (9 pts) Identify the origin of the designated lines as (star, warmer cloud, cooler cloud). In a single sentence below, briefly justify your answers:

A:

B:

C:

b) (5 pts) If the warm cloud is stationary with respect to the Earth, describe the motion of the cool cloud (also stationary, moving toward or moving away). Justify your answer.

8) Suppose we are observing an expanding supernova remnant (a thin, roughly spherical shell of hot gas). We know that the gas is centered on a position 1000 light years away from us. We also know that the shell itself has anangular size of 30 arcminutes. Based on Doppler shift information, we can deduce the speed of the expanding shell (and we assume it has remained constant over time). Explain how we would use this information in order to determine the approximate date that the supernova apparently went off. You donıt need to do all the math, just explain what you would do.