# Astronomy 300: Homework Assignment #9

Due: Friday, May 4th

Ch 8 in Croswell:

1. What is a subdwarf? How are they different from dwarfs? Who reported the first strong evidence for subdwarfs, and how was this discovery greeted by the astronomy establishment?

2. Studying subdwarfs at Yerkes Observatory in the 1950's, Nancy Roman made a remarkable discovery: Stars that emit an excessive amount of ultraviolet light move through the galaxy with higher (U, V, W) velocities. Explain how these two seemingly unrelated properties (motion and ultraviolet emission) are connected, using the idea of Stellar Populations. Also, why didn't Roman continue her work at Yerkes?

Ch 13 in C&O:

3. Estimate the main sequence lifetime (or nuclear timescale) of Proxima Centauri using the concepts shown for the Sun in Example 10.3.2 (p. 300) but with:
MProxima = 0.123 MSUN,
LProxima = 0.0017 LSUN

There is one major difference in this calculation, due to Proxima's internal structure. What is is?

4. C&O Problem 13.8 (2 points) Note that (') means arcminutes while (") is arcseconds.

5. C&O Problem 13.11

Ch 15 in C&O:

6. How is a Type Ia supernova different from at Type II supernova? Which is a good standard candle and why?

7. Look up the Radius and Mass of Sirius B, the first white dwarf to be discovered. Compute the density of the white dwarf in solar units and SI units. How much would one cubic centimeter of a White Dwarf weigh (on earth's surface)?

8. What keeps White Dwarfs from collapsing under their own gravity? Explain how a White Dwarf is supported differently from the Sun.

9. Textbooks sometimes state, eg.: "A teaspoon of neutron star material would weigh as much as...all the people on Earth ...or as much as a mountain". Try to determine the mass of 1 teaspoon of neutron star material. 1 tablespoon = 5 cubic centimeters. Hint: Neutron stars are made of pure neutrons.