Physics 112 Name_______________________________

Astronomy

Dr. Kolan

EXAM 3

April 30, 2003

I pledge my honor that during this examination I have neither given nor received assistance, and that I have seen no dishonest work.

Signed________________________________

I have intentionally not signed the pledge.__________________________

1) Label the following statements true or false. If a statement is false, explain why it is false. (5 pts apiece)

a) A M star has dark Balmer lines.

b) Chemical composition is the dominant factor in determining the spectral type of a star.

c) Stars on the main sequence are fusing helium into carbon.

d) A red star and a blue star both have the same radius and both are the same distance from the Earth. The blue star appears brighter to us.

e) It's going to take me light years to finish this test.

f) Star clusters with lots of dim, red are generally younger than clusters that don't have any such stars.

g) Given only the spectrum of a star and an HR diagram, you can find the distance to a star.

h) White dwarfs are very luminous because they are extremely hot.

2) Arrange the following stars (by labelling them 1-4) in order of age (1=youngest). Also give the evolutionary state of the stage, i.e. red giant, neutron star, etc. (5 pts apiece)

a. A star with no nuclear reactions. The star is made primarily of carbon and oxygen.

b. A star that is fusing hydrogen to helium in its core.

c. A star that is fusing helium to form carbon in the core and hydrogen to form helium in a shell around the core.

d. A star that is shedding its outer layers, revealing a core of carbon and oxygen

3) Below is a list of equations that are used to find the properties of stars. For each, tell what all of the symbols in the equation represent. Indicate which quantities are MEASURED and which is CALCULATED from the equation. Indicate HOW the measured quantities are obtained (i.e. from the spectrum, from a photometer, etc.) (5 pts apiece)

a)   p = 1/d

b)    P²=(4p²(R₁ + R₂)³⁾/(G (M₁ + M₂) Assume a spectroscopic binary here.

c) Dl/l = v/c

4) Regulus is a B7 V star (remember that the V indicates that it is main sequence). It is .076 times as bright as Sirius. Sirius is 8.61 light years away. You will need to use the diagrams on the last pages to complete this problem. (5 pts apiece)

a) What is Regulus's luminosity in terms of the solar luminosity? (5 pts)

b) What is the radius of Regulus in terms of solar radii? (5 pts)

c) What is the distance to Regulus in light years? (5 pts)

d) What is the mass of Regulus (in solar masses)? (5 pts)

e) What is the lifetime of Regulus? (5 pts)

Useful equations