Astronomy C

Test your knowledge of various Science Olympiad events.
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antoine_ego
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Astronomy C

Postby 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

Postby 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?

Answer
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Re: Astronomy C

Postby 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?

Answer

Correct! Your turn!
Rest in Peace Len Joeris

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Re: Astronomy C

Postby 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?

Answer

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

Postby 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

Postby 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

Postby 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.


Image
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Re: Astronomy C

Postby Unome » September 12th, 2017, 7:26 pm

Attempt
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 region 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 F3III. As far as I can tell, the apparent magnitude and apparent visual luminosity were unneeded.
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Re: Astronomy C

Postby PM2017 » September 12th, 2017, 8:19 pm

Unome wrote:
Attempt
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 region 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 F3III. 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

Postby 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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Re: Astronomy C

Postby PM2017 » September 14th, 2017, 7:31 pm

Unome wrote: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?

Image


b. The most prominent line is from C III / C IV
c. WR stars are in far stages of evolution, and have their stellar wind has blown away most of its outer nonmetallic elements (H and He). This allows for heavier elements (like carbon) to be more prominent in their spectra. (This information is a large amount of what I know about WR stars, and if you wanted the reason as to why this star has C III/ C IV lines rather than some form of Nitrogen, I'm sorry.)
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Re: Astronomy C

Postby Unome » September 15th, 2017, 5:14 am

Correct, your turn (though you didn't explicitly answer #1, your answer includes most of it). Also, from what I know, the subtypes of Wolf-Rayet stars are mostly dependent on mass and age, since that determines which elements are brought to the surface.
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Re: Astronomy C

Postby PM2017 » September 16th, 2017, 7:23 pm

Sorry this is so late.

In a binary system, one of the stars has a surface temperature of 7000K. The semimajor axis is 2.29 AU, and the period is 2 years. Find the luminosity of the other star, assuming both stars are in the main sequence, and that for main sequence stars Luminosity = Mass^3.5.

(EDIT: Both stars are more massive than the sun)
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Re: Astronomy C

Postby raxu » October 6th, 2017, 3:50 pm

PM2017 wrote:Sorry this is so late.

In a binary system, one of the stars has a surface temperature of 7000K. The semimajor axis is 2.29 AU, and the period is 2 years. Find the luminosity of the other star, assuming both stars are in the main sequence, and that for main sequence stars Luminosity = Mass^3.5.

(EDIT: Both stars are more massive than the sun)


We first calculate the combined mass of the star: . Looking at a table, star 1 is a G2 star with mass , so the other has mass . Finally, using the formula, the other has luminosity .

A supernova has peak apparent magnitude 18, and the H-alpha line appears at 670 nm. What is its peak absolute magnitude? Assume Hubble's constant is 72km/s/Mpc.
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Re: Astronomy C

Postby Adi1008 » October 7th, 2017, 1:37 pm

raxu wrote:
PM2017 wrote:Sorry this is so late.

In a binary system, one of the stars has a surface temperature of 7000K. The semimajor axis is 2.29 AU, and the period is 2 years. Find the luminosity of the other star, assuming both stars are in the main sequence, and that for main sequence stars Luminosity = Mass^3.5.

(EDIT: Both stars are more massive than the sun)


We first calculate the combined mass of the star: . Looking at a table, star 1 is a G2 star with mass , so the other has mass . Finally, using the formula, the other has luminosity .

A supernova has peak apparent magnitude 18, and the H-alpha line appears at 670 nm. What is its peak absolute magnitude? Assume Hubble's constant is 72km/s/Mpc.

Answer
about -16.7?
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