Title: Week 4 Quiz
Course: ASTRON103: The Evolving Universe: Stars, Galaxies, and Cosmology (001) DHH SU18 > Section: Week 4

Q: H II regions can exist only if there is a nearby star hot enough to ionize hydrogen. Hydrogen is ionized only by radiation with wavelengths shorter than 91.2 nm. What is the temperature of a star that emits its maximum energy at 91.2 nm? What law can you use to determine this temperature?

Q: The figure below shows radial velocity observations for two stars in a binary system. Which star, Star A or Star B, has a larger mass? How do you know?

Q: Two stars, Alpha and Beta, in a binary system have Luminosities of 1500 Solar Luminosities and 300 Solar Luminosities, respectively. If both stars have the same Temperature, which star is larger in size? How much bigger is the larger star than the smaller companion? Explain how you determined your answer.

Q: H I ("H-one") is used to denote neutral Hydrogen and is typically observed using 21-cm radio wavelengths.

What do we mean we talk about H II ("H-two")? Is it possible to have H III? Explain.

Q: The interstellar medium has an average density of 1 atom per cubic cm (1 atom/cm^3). If our Sun is made up of about 10^57 atoms, how large of a volume of the interstellar medium (in cubic light years, or ly^3) would you need in order to gather enough atoms to make up the Sun? Show your work and briefly explain your process.

Q: During sunset, the Sun tends to look much redder in the sky than when it is higher up during the day. Briefly explain why this happens. How does this process relate to the appearance of other more distant stars in our Galaxy?

Q: Explain why it is easier to measure the distance to a Cepheid that has a lower Luminosity than the distance to a Cepheid with a higher Luminosity.

Q: On an H-R Diagram, you notice a subset of stars near the bottom left end of the diagram. What kinds of stars are these and what was the first one observed?

Q: In order for a star to be on the main sequence, what key process must be happening within the star?

Q: What are the luminosity class and spectral type of a star with an effective temperature of 4500 K and a luminosity of 100 L_Sun?