Announcements • Homework: Supplemental Problems • Next exam is scheduled for April 1. It will be delayed one week to April 8. A formula sheet for it has been posted.
Most stars are on the Main Sequence Stars on the Main Sequence are fusing hydrogen into helium Stars on the Main Sequence are in equilibrium: outward pressure of the energy produced balances the inward pressure of gravity
The luminosity of a star on the main sequence depends on its mass A log(luminosity) versus log(mass) plot shows a straight line for main sequence stars above about 0.5 MSun A straight line on a log-log plot means there is a power relationship between the two quantities. The slope of the line gives the power.
The mass-luminosity relationship is a simple power law If the mass is given in Msun then the luminosity is in LSun
Examples The star Sirius has a luminosity 23 times that of the Sun. What is its mass? What is the luminosity of a star with a mass of 0.75 Msun?
Example Solution Solve the Mass-Luminosity relationship for mass and plug in the numbers Given the mass, just plug in the value to get the luminosity
Examples How long will a 3.5 solar mass star live on the main sequence? How long will a 0.5 solar mass star live on the main sequence?
Example Solution Just plug in the numbers and grind away on the calculator