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Can Luminosity Give You a Star's Age?

by chefskitten
Tags: luminosity, star
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chefskitten
#1
Oct25-13, 09:33 PM
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You find two yellow stars at the same distance (but not in a binary system!). They have the same mass, but one is much more luminous than the other.
Which one is older?
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howabout1337
#2
Oct26-13, 10:58 AM
P: 21
http://en.wikipedia.org/wiki/Stellar_age_estimation:
"As stars grow older, their luminosity increases at an appreciable rate"

So I would assume the more luminous one.
chefskitten
#3
Oct27-13, 08:54 PM
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Thanks for your input howabout1337! That's what I was thinking, just wanted some confirmation

phinds
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Oct27-13, 09:16 PM
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Can Luminosity Give You a Star's Age?

I don't get it. How would you tell an old modest-sized star from a large younger star, both of which have the same luminosity?
Chronos
#5
Oct27-13, 10:46 PM
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The luminosity of a star is strongly dependent on mass, which is known as the mass-luminosity relationship. While the luminosity of a star does increase somewhat with age, the difference is small until it leaves the main sequence. It would be a wildly unreliable way to determine the age of a star.
Drakkith
#6
Oct28-13, 01:35 AM
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Quote Quote by phinds View Post
I don't get it. How would you tell an old modest-sized star from a large younger star, both of which have the same luminosity?
The more massive one has a different spectrum. It will be hotter, even if their luminosity is the same.
Drakkith
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Oct28-13, 01:37 AM
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Quote Quote by Chronos View Post
The luminosity of a star is strongly dependent on mass, which is known as the mass-luminosity relationship. While the luminosity of a star does increase somewhat with age, the difference is small until it leaves the main sequence. It would be a wildly unreliable way to determine the age of a star.
Do you know if this graph is accurate? This seems to be a pretty big change.
From here: http://en.wikipedia.org/wiki/Sun#Main_sequence

Vanadium 50
#8
Oct28-13, 08:16 PM
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It's at least approximately right. When I studied these things, the sun went off the main sequence a little sooner and more quickly (9.1 BY), but there's a factor of ~2 or so luminosity increase over the course of the main sequence.
Chronos
#9
Oct28-13, 10:00 PM
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When the sun first entered the main sequence, it was about 70% of its current luminosity. Over the next 4.5 billion years, it's luminosity is expected to increase by about 67%. I do not consider that enough of a luminosity difference to be useful to estimate the age of a star.


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