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