Astronomy 2, Spring 2007

 

Homework set 6, due May 29 .

 

1. Here is a list of properties of stars.  Each of these properties can be measured by some kind of observations from earth. For each property, answer the following questions, explaining your answers clearly:  (a) Can it be measured with a single observation, or does it require multiple times at the telescope? (b) What kind of observation(s) is necessary to measure it (spectra, position, etc.)? (c) Can it be measured for a single star, or does it require more than a single star or even require a group of stars?

 

(a) The chemical composition of a star.

(b) The radial velocity of a star.

(c) The distance of a star closer than 100 pc.

(d) The apparent magnitude of a star.

(e) The temperature of a star.

(f) The age of a star.

(g) The mass of a star.

(h) The absolute magnitude of a star.

 

2.Energy transport in the sun.

 

(a) Why do neutrinos give us different information about the sun than light does?

(b) What would happen to the sun if, for some reason, gravity were to stop working?

(c) What would happen if the sun lost its ability to produce internal pressure?

(d) What would happen to the sun if it suddenly became completely transparent to light?

(e) Someday the sun will change from its current size. What will happen to make the sun do this?

 

3. Ages of clusters.  The stars in globular and galactic clusters are often plotted on an H-R Diagram.  Explain the physical reasoning behind the use of the main sequence turn-off as a way of age-dating the cluster. Make up your own cluster and plot in on an H-R diagram.  You can decide where the main sequence turn-off point is.  How old is your cluster? Explain.

 

4. End-stages of a starŐs life.

 

(a) What are the possible end-stages of stars? What primarily determines the end-stage of a particular star?

(b) What are the kinds of forces that provide support against gravity, if there is anything to support, in each of these cases?

(c) What are the sources of energy that provide the luminosity for stars in each of these end-stages?

 

5. Star formation.

 

(a) What is the Kelvin-Helmholtz energy generation mechanism? What kind of energy does it tap?  Why is it inadequate for our current sun?

(b) During what stages of stellar evolution is the Kelvin-Helmholtz mechanism the major source of energy generation?  Explain.

(c) A what wavelength region do we see proto-stars best?  Why?

 

6.Stars and their evolution.  Using a connecting line, match each of the objects to the proper description.

 

                        1. pulsar                                                                    a. used to be the outer envelope of a star

                        2. supernova                                                       b. a star burning hydrogen in its core

                        3. dwarf star                                                        c. ultimately the fate of our sun

                        4. planetary nebula                                  d. rapidly rotating neutron star

                        5. red giant                                                           e. compact, partially degenerate core and large extended envelope

                        6. black hole                                                      f. catastrophic explosion of a massive star

                        7. white dwarf                                                 g. object from which not even light can escape