Astronomy C

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Re: Astronomy C

Postby raxu » October 8th, 2017, 9:02 am

Adi1008 wrote:
Answer
about -16.7?

Solution (math mode used)
We first find the velocity. H-alpha line usually appears at .

By , we find that .

Then, using , we find .

Plugging into distance modulus , we get .

Can someone check that the doppler shift equation I used was correct? Thanks!

Also, your turn Adi1008!
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Re: Astronomy C

Postby Adi1008 » October 8th, 2017, 2:10 pm

raxu wrote:
Adi1008 wrote:
Answer
about -16.7?

Solution (math mode used)
We first find the velocity. H-alpha line usually appears at .

By , we find that .

Then, using , we find .

Plugging into distance modulus , we get .

Can someone check that the doppler shift equation I used was correct? Thanks!

Also, your turn Adi1008!

I believe the equation that you used for redshift is fine as long as the recession speeds are not relativistic. Once the objects get very far away, things like comoving distance become important, so the equation gets more complex.

Image
A, B, C, and D represent 4 pulsars. Which one's kinetic energy is decreasing the fastest? Assume (somewhat wrongly) that the moment of inertias of each pulsar are all about the same
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Re: Astronomy C

Postby jonboyage » October 8th, 2017, 2:55 pm

Answer
Pulsar A is losing energy the fastest because it is slowing down more rapidly than C or D and it has a quicker initial period than B (and energy increases quadratically with angular velocity, so the same linear decrease at a lower period correlates with faster energy loss)
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Re: Astronomy C

Postby Adi1008 » October 8th, 2017, 8:32 pm

jonboyage wrote:
Answer
Pulsar A is losing energy the fastest because it is slowing down more rapidly than C or D and it has a quicker initial period than B (and energy increases quadratically with angular velocity, so the same linear decrease at a lower period correlates with faster energy loss)

Correct, your turn!
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Re: Astronomy C

Postby jonboyage » October 9th, 2017, 2:15 pm

A few questions about pulsars and magnetars:

a. Briefly explain how we, from Earth, measure magnetic fields of stellar objects. (mention an effect, starts with a "z")

b. We know that pulsars already have very strong magnetic fields, along which beams of radiation emerge. What, during their formations, causes magnetars to have significantly stronger magnetic fields than other pulsars?

c. What causes magnetars to maintain very strong magnetic fields long after their formation?

d. Does this mean that neutron stars are not completely made of neutrons? :o What are they actually made of? (name at least 3 particles)

e. Is there another particle present in the interiors of neutron stars that starts with an "h"?

f. Ew, what is this new particle that I've never heard of (although it does sound cool) and what are two ways it affects the neutron star in the long run?
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Re: Astronomy C

Postby c0c05w311y » October 17th, 2017, 2:57 am

Answer:
A: The Zeeman Effect. This effect causes spectral lines to split in the presence of magnetic fields, and we can measure this splitting.
B: Rotational energy is converted into a magnetic field due to a dynamo process in the conducting fluid of a magnetar as it is forming.
C: Magnetars retain their magnetic field due to currents in proton-superconducting matter within the neutron star.
D: mostly neutrons of course, but also protons and electrons.
E: Hyperons are thought to exist in the core of neutron stars. They are baryons made of up, down, and strange quarks.
F: It effects the rate of cooling or something, and has to do with gravitational waves??? I don't know anything about this really.

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Re: Astronomy C

Postby jonboyage » October 18th, 2017, 4:40 pm

c0c05w311y wrote:
Answer:
A: The Zeeman Effect. This effect causes spectral lines to split in the presence of magnetic fields, and we can measure this splitting.
B: Rotational energy is converted into a magnetic field due to a dynamo process in the conducting fluid of a magnetar as it is forming.
C: Magnetars retain their magnetic field due to currents in proton-superconducting matter within the neutron star.
D: mostly neutrons of course, but also protons and electrons.
E: Hyperons are thought to exist in the core of neutron stars. They are baryons made of up, down, and strange quarks.
F: It effects the rate of cooling or something, and has to do with gravitational waves??? I don't know anything about this really.


That's just about correct. Parts E and F were mostly for fun so those answers are acceptable. Your turn!
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Re: Astronomy C

Postby c0c05w311y » October 20th, 2017, 6:20 am

Some questions about variable stars and related topics:

1. What is the mechanism of variability for classical cepheid stars? Name the specific process/mechanism and explain what it is.

2. What determines whether a section of a star is primarily convective or radiative? Which sections of high/low mass stars are convective/radiative?

3. How is it possible for LBV stars to exceed their Eddington luminosity?

4. What principle is the Eddington Luminosity based on? How do you calculate the Eddington luminosity?

5. What are the two instability strips on the HR diagram, and what kinds of stars are found in each?

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Re: Astronomy C

Postby PM2017 » January 16th, 2018, 4:39 pm

c0c05w311y wrote:Some questions about variable stars and related topics:

1. What is the mechanism of variability for classical cepheid stars? Name the specific process/mechanism and explain what it is.

2. What determines whether a section of a star is primarily convective or radiative? Which sections of high/low mass stars are convective/radiative?

3. How is it possible for LBV stars to exceed their Eddington luminosity?

4. What principle is the Eddington Luminosity based on? How do you calculate the Eddington luminosity?

5. What are the two instability strips on the HR diagram, and what kinds of stars are found in each?


This thread has been dead for far too long.
1. I don't know how to write greek letters here, but its called the kappa mechanism, Kappa denotes opacity here. basically, because of compression (decrease of volume) in the stellar atmosphere, increase in temperature and pressure occurs, which ionizes He I to He II, which is more opaque. This means that the He II absorbs radiation, making it hotter. In turn, this will expand the star, make it cooler, since it will radiate more energy away. Since it's cooler, the He II takes an electron and becomes He I, which is transparent, and lets light through. Then, since it isn't as hot, it will shrink again, and process repeats.
2. Mass. High mass stars have convective cores, and radiative envelope (don't know if that's the right word). This is the opposite in lower mass stars.
3.I'm not sure how correct this is, but I believe that the Eddington luminosity talk about the brightest a stable object without losing mass. LBVs are unstable, and when they do exceed the Eddington Luminosity, LBV stars are shedding a significant amount of mass, and are unstable.
4.The Eddington Luminosity is the theoretical maximum luminosity of a hydrostatically stable object. (It is the luminosity that an object would have to be to generate enough outward force to match/exceed gravitational force) It is calculated by setting the outward force to the gravitational force and solving for luminosity.
5.I thought there was only one instability strip, and so I don't know the answer to this one. I'm still posting though, to revive this thread.
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Re: Astronomy C

Postby c0c05w311y » January 17th, 2018, 9:11 am

PM2017 wrote:
c0c05w311y wrote:Some questions about variable stars and related topics:

1. What is the mechanism of variability for classical cepheid stars? Name the specific process/mechanism and explain what it is.

2. What determines whether a section of a star is primarily convective or radiative? Which sections of high/low mass stars are convective/radiative?

3. How is it possible for LBV stars to exceed their Eddington luminosity?

4. What principle is the Eddington Luminosity based on? How do you calculate the Eddington luminosity?

5. What are the two instability strips on the HR diagram, and what kinds of stars are found in each?


This thread has been dead for far too long.
1. I don't know how to write greek letters here, but its called the kappa mechanism, Kappa denotes opacity here. basically, because of compression (decrease of volume) in the stellar atmosphere, increase in temperature and pressure occurs, which ionizes He I to He II, which is more opaque. This means that the He II absorbs radiation, making it hotter. In turn, this will expand the star, make it cooler, since it will radiate more energy away. Since it's cooler, the He II takes an electron and becomes He I, which is transparent, and lets light through. Then, since it isn't as hot, it will shrink again, and process repeats.
2. Mass. High mass stars have convective cores, and radiative envelope (don't know if that's the right word). This is the opposite in lower mass stars.
3.I'm not sure how correct this is, but I believe that the Eddington luminosity talk about the brightest a stable object without losing mass. LBVs are unstable, and when they do exceed the Eddington Luminosity, LBV stars are shedding a significant amount of mass, and are unstable.
4.The Eddington Luminosity is the theoretical maximum luminosity of a hydrostatically stable object. (It is the luminosity that an object would have to be to generate enough outward force to match/exceed gravitational force) It is calculated by setting the outward force to the gravitational force and solving for luminosity.
5.I thought there was only one instability strip, and so I don't know the answer to this one. I'm still posting though, to revive this thread.


Nice! Back when I wrote this, I think I was referring to the S. Doradus instability strip / area for number 5. I've seen some test questions on what kind of stars (WR, LBV, O class giants ...) are located where in this area, so its nice to have a diagram. There's really only one instability strip people refer to when they say "the instability strip," you're right about that.

Your turn!

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Re: Astronomy C

Postby Unome » January 17th, 2018, 9:36 am

c0c05w311y wrote:
PM2017 wrote:
c0c05w311y wrote:Some questions about variable stars and related topics:

1. What is the mechanism of variability for classical cepheid stars? Name the specific process/mechanism and explain what it is.

2. What determines whether a section of a star is primarily convective or radiative? Which sections of high/low mass stars are convective/radiative?

3. How is it possible for LBV stars to exceed their Eddington luminosity?

4. What principle is the Eddington Luminosity based on? How do you calculate the Eddington luminosity?

5. What are the two instability strips on the HR diagram, and what kinds of stars are found in each?


This thread has been dead for far too long.
1. I don't know how to write greek letters here, but its called the kappa mechanism, Kappa denotes opacity here. basically, because of compression (decrease of volume) in the stellar atmosphere, increase in temperature and pressure occurs, which ionizes He I to He II, which is more opaque. This means that the He II absorbs radiation, making it hotter. In turn, this will expand the star, make it cooler, since it will radiate more energy away. Since it's cooler, the He II takes an electron and becomes He I, which is transparent, and lets light through. Then, since it isn't as hot, it will shrink again, and process repeats.
2. Mass. High mass stars have convective cores, and radiative envelope (don't know if that's the right word). This is the opposite in lower mass stars.
3.I'm not sure how correct this is, but I believe that the Eddington luminosity talk about the brightest a stable object without losing mass. LBVs are unstable, and when they do exceed the Eddington Luminosity, LBV stars are shedding a significant amount of mass, and are unstable.
4.The Eddington Luminosity is the theoretical maximum luminosity of a hydrostatically stable object. (It is the luminosity that an object would have to be to generate enough outward force to match/exceed gravitational force) It is calculated by setting the outward force to the gravitational force and solving for luminosity.
5.I thought there was only one instability strip, and so I don't know the answer to this one. I'm still posting though, to revive this thread.


Nice! Back when I wrote this, I think I was referring to the S. Doradus instability strip / area for number 5. I've seen some test questions on what kind of stars (WR, LBV, O class giants ...) are located where in this area, so its nice to have a diagram. There's really only one instability strip people refer to when they say "the instability strip," you're right about that.

Your turn!

I wondered whether it was the S Doradus one. Some sources separate the kappa mechanism instability strip (and related) from variable white dwarfs (which I think operate on a similar mechanism, though I can't remember).
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Re: Astronomy C

Postby PM2017 » January 17th, 2018, 1:01 pm

Quick question before I post my next set of questions. Can someone teach me how to add images that are saved on my computer, to a post?
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Re: Astronomy C

Postby jonboyage » January 17th, 2018, 1:11 pm

PM2017 wrote:Quick question before I post my next set of questions. Can someone teach me how to add images that are saved on my computer, to a post?


You can use an image-hosting website like i.imgur
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Re: Astronomy C

Postby PM2017 » January 18th, 2018, 4:28 pm

Since I don't have enough time to upload to imgur, (never procrastinate on Mission Possible...) I'll just ask non-image related dso questions.

1) I am thought to be the youngest known black hole in the Milky Way, ignoring light travel time. Who am I?
a. What is interesting about the PNe surrounding me?
b. What type of star was my progenitor?
c. If there was a classical Cepheid in place, with a period of 25 days, what would the apparent magnitude of the Cepheid be?

2) I am the largest known yellow hypergiant. Who am I?
a. Which of the following other names do I go by (select all that apply)? A. AAVSO 0549+07 B. HIP 67261 C. V766 Cen D. 1ES 1908+09 E. HD 35343 F. AAVSO 1340-62
b. What is my evolutionary track? (What types of stars will I become over time.)
c. What is my radius?

3) I am the first known radio-quiet pulsar. Who am I?
a. Instead of radio, I am a bright source of what type of radiation.
b. What is my rotational period?
c. If I was 1 parsec away from the earth, what would my apparent magnitude be?
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Re: Astronomy C

Postby c0c05w311y » January 19th, 2018, 1:00 pm

Answer:
1. W49B
a. Iron is only in half the remnant, and other things including silicon and sulfur were evenly spread. Also, It shows x-ray emission from chromium and manganese.
b. The SN is type 1b/1c probably, which means the progenitor was probably an LBV/WR with a lot of mass loss. Wikipedia says the progenitor was probably around 25 solar masses.
c. Given a period of 25 days, we can calculate the absolute magnitude using the period luminosity relationship. M = -2.8log(25 days) - 1.43 gives an absolute magnitude of M = -5.34. Using m - (-5.34) = -5+5log(7972 pc) gives m = 9.17.


2. HR 5171A
a. B, C, F, i think
b. its currently a yellow hypergiant, which is a pretty unstable state that is probably between red supergiant and blue supergiant stages, which explains why we see so few of them. I don't know if HR5171A is moving towards a bluer or redder stage, but it could become a blue supergiant, a red supergiant, or (very unlikely, it might be able to go supernova directly). It could shed it's outer envelope and become a WR binary. Eventually it will explode in a type 2 (probably P but it depends on how much mass loss in later stages) or type 1b/1c (especially if there is more mass loss such as if it enters a WR stage) supernova, and probably leave behind a black hole.
c. 1315 to 1575 solar radii


3. Geminga
a. gamma
b. 273 ms
c. 13.51


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