In the outer halo of a nearby galaxy the brightest red giants pile up at an apparent…

PHYSICS · Multi-part · Fermi University Physics · Astrophysics & Cosmology · Stellar structure, energy generation and evolution · Stellar structure, energy generation and evolution

Stars from the Inside, Ch Stellar evolution: from the Hayashi track to the iron core, and the ages of clusters

Problem

In the outer halo of a nearby galaxy the brightest red giants pile up at an apparent magnitude I=25.0I = 25.0, already corrected for dust. Take the tip of the red giant branch to have absolute magnitude MI≈−4.05M_I \approx -4.05. ((a)) Find the galaxy's distance modulus and its distance in megaparsecs. ((b)) Suppose helium ignited at a core mass of 0.46 M⊙0.46\,M_\odot rather than 0.47 M⊙0.47\,M_\odot. Using L∝Mc6L\propto M_c^{6}, by what fraction would the tip luminosity fall, and by what fraction would the distance in part (a) be overestimated if the calibration MI≈−4.05M_I\approx-4.05 were kept?

Browse the problem library