Astronomy C

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Astronomy C

Post by antoine_ego » September 5th, 2017, 12:10 pm

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

Let's start with the classic.

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

Post by Adi1008 » September 5th, 2017, 2:01 pm

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?
[math]\Big(\frac{300}{365}\Big)^{2} = \frac{a^{3}}{15} \rightarrow a \approx 2.16 \mathrm{AU}[/math]
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Re: Astronomy C

Post by antoine_ego » September 5th, 2017, 2:30 pm

Adi1008 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?
[math]\Big(\frac{300}{365}\Big)^{2} = \frac{a^{3}}{15} \rightarrow a \approx 2.16 \mathrm{AU}[/math]
Correct! Your turn!
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2018 Nationals - Team 9th Place!
2019 Astronomy Nationals - 3rd!
2019 Nationals - Team 9th Place!
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Re: Astronomy C

Post by Adi1008 » September 5th, 2017, 6:02 pm

antoine_ego wrote:
Adi1008 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?
[math]\Big(\frac{300}{365}\Big)^{2} = \frac{a^{3}}{15} \rightarrow a \approx 2.16 \mathrm{AU}[/math]
Correct! Your turn!
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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Re: Astronomy C

Post by PM2017 » September 11th, 2017, 7:46 am

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

Post by Adi1008 » September 12th, 2017, 5:56 pm

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
Looks good! Your turn.
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Re: Astronomy C

Post by PM2017 » September 12th, 2017, 6:35 pm

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

Post by Unome » September 12th, 2017, 7:26 pm

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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Re: Astronomy C

Post by PM2017 » September 12th, 2017, 8:19 pm

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.
Your answer to question b. was correct Your answer for a. was quite close. The real answer was A7V.
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

Post by Unome » September 13th, 2017, 7:32 am

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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