•Q4.
Spectroscopic parallax.
(Apparent) magnitude = 5.4 for an O6 V star. How far away is it?
First need to get an absolute magnitude. Can estimate it several ways (H-R diagrams, mass-luminosity
relation). I used M = -5.6. So:
•d (pc) = 10 (m-M+5)/5 = 103.2 = 1585 parsecs
•
•Q5. If we discover a type 1a supernova in a distant
galaxy that at its brightest has
an apparent magnitude of 17, how far away is the galaxy? (Assume the supernova has an absolute magnitude of -19.)
•d (pc) = 10 (m-M+5)/5 = 108.2 = 1.6x108 pc x 1Mpc/106pc = 160
Mpc
•
•Q6. The
“Blade Runner Question.”
A star that burns half the lifetime of the sun does not burn twice as bright. How bright (luminous) is it?
• Lifetime in solar units = M-2.5 (solar
m)
• 0.5 = M-2.5
• M2.5 = 2
• M =
(2)1/2.5 = 20.4= 1.3 solar masses
• L in solar units = M3.5 (solar
units)
• Luminosity = (1.3)3.5 = 2.6 solar
•