Help to determine the luminosity of a star

In summary, the luminosity of these stars is calculated using a different method to the visual magnitude.
  • #1
victoriafello
34
0
I need to work out the luminosity of 3 stars 85 PEG A / B / C using the following data and equation,

Absolute Mag of stars A/B/C/SUN
MA = 5.28
MB = 8.53
MC = 15
MS = 4.84
Apparent Mag of stars A/B/C
mA = 5.75
mB = 9.00
mC = 15.47
LS = Luminosity of Sun – 1 ?

Equation
MA-MS = -2.5 LOG ( LA/LS)

I have got a result of 0.667 for A and 0.033 for B, But when i have looked online at star catalogues the actual lumisosity is different, where am i going wrong ?
 
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  • #2
victoriafello said:
I have got a result of 0.667 for A and 0.033 for B, But when i have looked online at star catalogues the actual lumisosity is different, where am i going wrong ?

What luminosities do the catalogues give for these stars? Even better, can you give links to these catalogues?
 
  • #3
I looked on a few sites at home which i can't remember now but one was on Wiki, i know that's not always the most reliable source so i wasnt sure if it was me or them that was incorrect


http://en.wikipedia.org/wiki/85_Pegasi
 
  • #4
victoriafello said:
I looked on a few sites at home which i can't remember now but one was on Wiki, i know that's not always the most reliable source so i wasnt sure if it was me or them that was incorrect


http://en.wikipedia.org/wiki/85_Pegasi


I thinks that this uses bolometric, not visual, magnitudes to calculate luminosities.
 
  • #5
I have been investigating the same question. I have used the same method as you but not sure if it is correct. Waiting for my tutor to get back to me whether they have told us to use the correct equation! Using the software Celestia A = 0.558 and B = 0.032 but i assume that is absolute luminosity. I will tell you if the tutor comes up with anything.
 
  • #6
I have been lead to believe that my values (the same as yours for this question) have been calculated in the correct way. If you used the Celestia software, which is good fun and recommend but can't find the link at the mo, sorry, and use their figs for M then you get closer to their values for L. One bonus from going through countless pieces of paper and lots of pencil lead is that I am now quite au fait with solving log equations!
My tutor has been brillant on this matter and actually bothered to look at the question unlike the tutor on my other course when there were queries.
Good luck with the rest of the paper.
 

1. How is luminosity measured?

Luminosity is measured by calculating the total amount of energy radiated by a star in all directions, also known as its total power output. This is typically measured in joules per second, or watts.

2. What factors influence a star's luminosity?

The main factors that influence a star's luminosity are its size, temperature, and composition. A larger star with a higher temperature and more elements will have a higher luminosity compared to a smaller, cooler star.

3. How is a star's luminosity related to its brightness?

A star's luminosity is directly related to its brightness. However, this can be misleading as a star's brightness also depends on its distance from Earth. A star with a high luminosity may appear dimmer if it is far away, while a less luminous star may appear brighter if it is closer.

4. Can a star's luminosity change over time?

Yes, a star's luminosity can change over time. This can happen due to changes in the star's internal structure, such as nuclear reactions or changes in temperature. A star's luminosity may also change due to external factors, such as interactions with other stars in a binary system.

5. How can determining a star's luminosity help us understand its lifespan?

Determining a star's luminosity is crucial in understanding its lifespan. The more luminous a star is, the more energy it is using up and the faster it will exhaust its fuel. This means that a star with a higher luminosity will have a shorter lifespan compared to a less luminous star. By knowing a star's luminosity, we can make predictions about its future evolution and ultimate fate.

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