Homework Handout #12

12.01: A Cepheid variable in a hypothetical galaxy is observed to pulsate with a period of twelve days, and its apparent visual magnitude is 19. It is not known whether this is a Population I or Population II Cepheid. Using the Pop I Cepheid Period-Luminosity Relation from the lecture notes, plus the fact that Pop II Cepheids are about 4 times lower luminosity than Pop I:
(a) What are the two possible distances to the galaxy (neglect stellar absorption).
(b) What is the ratio of these distances?
(c) From the information given, would this ratio differ for Cepheids of other periods? Explain.

12.02: If our telescope can observe to a limiting magnitude of 22, what is the maximum distance (expressed in kpc, Mpc, or Gpc, as appropriate) to which we can see
(a) RR Lyrae stars
(b) classical Cepheids
(c) W Virginis (Pop II) Cepheids
(d) ordinary novae
(e) dwarf novae
(f) supernovae
How do these distances compare with the diameter of our galaxy (about 30 kpc)?