Astronomy C

[raxu]

Answer (Click to Show Hidden Text)

about -16.7?

Solution (math mode used) (Click to Show Hidden Text)

We first find the velocity. H-alpha line usually appears at [math]\lambda_0=656\text{nm}[/math].

By [math]\frac{\Delta\lambda}{\lambda_0}=\frac{v}{c}[/math], we find that [math]v=6402km/s[/math].

Then, using [math]v=H_0d[/math], we find [math]d=89Mpc[/math].

Plugging into distance modulus [math]M=m-5\log_{10}(\frac{d}{10\text{pc}})[/math], we get [math]M=-16.7[/math].

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

Also, your turn Adi1008!

[Adi1008]

Answer (Click to Show Hidden Text)

about -16.7?

Solution (math mode used) (Click to Show Hidden Text)

We first find the velocity. H-alpha line usually appears at [math]\lambda_0=656\text{nm}[/math].

By [math]\frac{\Delta\lambda}{\lambda_0}=\frac{v}{c}[/math], we find that [math]v=6402km/s[/math].

Then, using [math]v=H_0d[/math], we find [math]d=89Mpc[/math].

Plugging into distance modulus [math]M=m-5\log_{10}(\frac{d}{10\text{pc}})[/math], we get [math]M=-16.7[/math].

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.


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

[jonboyage]

Answer (Click to Show Hidden Text)

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)

[Adi1008]

Answer (Click to Show Hidden Text)

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!

[jonboyage]

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? 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?

[c0c05w311y]

Answer: (Click to Show Hidden Text)

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.

[jonboyage]

Answer: (Click to Show Hidden Text)

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!

[c0c05w311y]

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?

[PM2017]

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.

[c0c05w311y]

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!