3. A star at a distance of 10pc from Earth has an apparent magnitude of +2.8. What is its luminosity in solar units? (Reminder: the absolute magnitude of the Sun is +4.8.) 0.2 Lo O 0.6 Lo 1.0 Lo O 6.3 Lo 100 Le 625 Le 4. About how long will a star with a mass of 0.25 Mo spend on the main sequence? 8 x 10' yr 3 x 10 yr 3 x 10' yr 4 x 1010 yr 3 x 10 yr Either answer will be accepted. 3x11 years 4 x 1013 yr is what you get if simply scale from the sun's lifetime. If you remembered that a 0.5 solar mass star lives Tell yrs, so a lighter star should live even longer, you will also get full credit. (We are in the process of doing a regrade of this question.) The "best" answer is really about 1. 5e12 years. 1067 Supergiants 104 102 Giants Luminosity (Lsun) Main Sequence 1+ 10-2+ 10-4 White Dwarfs: : 40,000 20,000 10,000 5,000 2,500 Temperature (K) 5. Using the H-R diagram given above, work out the radius of a main sequence star with a temperature of 10,000K. 1 x 10' m 5 x 10' m O 2 x 10' m 4 x 10 m O 1 x 101 m O impossible to determine from the given information