Problem for AY97

Distances and the Period-Luminosity Relation for Cepheids

The main ``Primary'' distance indicator in use today is the Period-Luminosity relation for Cepheid Variable stars. Cepheids are supergiants averaging several thousand times the luminosity of the Sun, so they can be see in external galaxies to moaderately large distances especially with the keen optics of the Hubble Space Telescope (HST).

The HST H0 Key Project and a few related programs have measured Cepheid based distances to about 25 galaxies, and more are slowly coming. I've created a data file with periods and magnitudes for ~a dozen galaxies, with absolute magnitudes (so you can get the real calibration of Magnitude vs log Period) for Cepheids in the Milky Way and apparent magnitude fo the other galaxies, pl.dat linked here. The problem for AY97 students is as follows. I will assign galaxies to each student in class. or problem.pdf