## Astronomy C

antoine_ego
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### Astronomy C

Short Event Description: Teams will demonstrate an understanding of stellar evolution and Type II Supernova Events.

Two stars A and B are in a binary system with combined mass 15 Msol. If the period of the system is 300 days, what is the separation of the two stars in AU?
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### Re: Astronomy C

antoine_ego wrote:Two stars A and B are in a binary system with combined mass 15 Msol. If the period of the system is 300 days, what is the separation of the two stars in AU?
$\Big(\frac{300}{365}\Big)^{2} = \frac{a^{3}}{15} \rightarrow a \approx 2.16 \mathrm{AU}$
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antoine_ego
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### Re: Astronomy C

antoine_ego wrote:Two stars A and B are in a binary system with combined mass 15 Msol. If the period of the system is 300 days, what is the separation of the two stars in AU?
$\Big(\frac{300}{365}\Big)^{2} = \frac{a^{3}}{15} \rightarrow a \approx 2.16 \mathrm{AU}$
Rest in Peace Len Joeris
[b]2016 Air Trajectory Nationals - 3rd
2018 Hovercraft Nationals - 6th
2018 Mousetrap Nationals - 6th
2018 Nationals - Team 9th Place!
2019 Astronomy Nationals - 3rd!
2019 Nationals - Team 9th Place!
[/b]
Acton-Boxborough Regional High School Captain 17-19

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### Re: Astronomy C

antoine_ego wrote:
antoine_ego wrote:Two stars A and B are in a binary system with combined mass 15 Msol. If the period of the system is 300 days, what is the separation of the two stars in AU?
$\Big(\frac{300}{365}\Big)^{2} = \frac{a^{3}}{15} \rightarrow a \approx 2.16 \mathrm{AU}$
Consider a star that has a radius of 900 solar radii and a surface temperature of 3500K.
(a) What is its luminosity, in solar luminosities?
(b) What is its absolute magnitude?
(c) What is the flux from the star, in W/m^2, at a distance of 100 AU?
(d) Suppose that from Earth, the star has an apparent magnitude of 0. How far away is this star, in parsecs?
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PM2017
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### Re: Astronomy C

This is the first question marathon that I will be participating, so I'll just copy what has been happening and post the answers that I got.
a. ~109000 L-sol
b. -7.7
c. ~15000 W/m^2
d. 347 pc

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### Re: Astronomy C

PM2017 wrote:This is the first question marathon that I will be participating, so I'll just copy what has been happening and post the answers that I got.
a. ~109000 L-sol
b. -7.7
c. ~15000 W/m^2
d. 347 pc
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PM2017
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### Re: Astronomy C

Alright! I've had this problem prepared for quite some time.

A star has an apparent visual brightness of (1.2635*10^-8W)/(m^2), an apparent magnitude of 0.76, an absolute magnitude of 2.2, and a λmax of 376.3 nm.
a. Find the spectral class (including numeric subdivision and luminosity class) of this star.
b. Select which region of the given H-R Diagram near which it would be plotted.

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### Re: Astronomy C

Comparing the Sun's absolute magnitude of ~4.85 to this star's absolute magnitude of 2.2, that yields 2.5^2.65 solar luminosities, which is about 11. Therefore, the star should be in [b]region B[/b]. This is supported by using Wien's law to calculate a temperature of ~7700 K. If I had my binder I would know the exact spectral class - however, based on the fact that the Sun is ~5800 K, this is probably somewhere around F3. I'd expect this to be a giant (guesstimate), so [b]F3III[/b]. As far as I can tell, the apparent magnitude and apparent visual luminosity were unneeded.
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PM2017
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### Re: Astronomy C

Unome wrote:
Comparing the Sun's absolute magnitude of ~4.85 to this star's absolute magnitude of 2.2, that yields 2.5^2.65 solar luminosities, which is about 11. Therefore, the star should be in [b]region B[/b]. This is supported by using Wien's law to calculate a temperature of ~7700 K. If I had my binder I would know the exact spectral class - however, based on the fact that the Sun is ~5800 K, this is probably somewhere around F3. I'd expect this to be a giant (guesstimate), so [b]F3III[/b]. As far as I can tell, the apparent magnitude and apparent visual luminosity were unneeded.
The reason that the two unneeded buts of information were there was the fact that I made this problem back when I didn't know a good way to convert between apparent visual luminosity and Absolute Magnitude. I decided to keep it in order to (possibly) confused people.

Well, you got the right answer to the more important question.
You know what to do!
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### Re: Astronomy C

Some theoretical stuff:

Refer to the image below.
1. This spectrum primarily shows the (visual/ultraviolet/near infrared) range, and is characteristic of a (Luminous Blue Variable/ZZ Ceti star/Wolf-Rayet star/Type II Cepheid).
2. What element causes the largest emission line on this spectrum?
3. Why does this type of star have such prominent emission lines?
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