## Astronomy C

raxu
Exalted Member
Posts: 41
Joined: October 9th, 2014, 6:54 pm
Division: C
State: NY

### Re: Astronomy C

Solution (math mode used)
Can someone check that the doppler shift equation I used was correct? Thanks!

Richard
Events done Div. B: Simple Machines , Shock Value.
Events done Div. C: Astronomy , It's About Time, Forensics, Optics, Remote Sensing, Game On, Materials Science, Mousetrap Vehicle, Fermi Questions, Thermodynamics.

Moderator
Posts: 472
Joined: December 6th, 2013, 1:56 pm
State: TX
Location: Austin, Texas

### Re: Astronomy C

Solution (math mode used)
Can someone check that the doppler shift equation I used was correct? Thanks!

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
University of Texas at Austin '22
Seven Lakes High School '18
Beckendorff Junior High '14

jonboyage
Member
Posts: 102
Joined: December 13th, 2016, 8:32 am
State: PA

### Re: Astronomy C

I was in a bin

Rustin '19
UPenn '23

Moderator
Posts: 472
Joined: December 6th, 2013, 1:56 pm
State: TX
Location: Austin, Texas

### Re: Astronomy C

University of Texas at Austin '22
Seven Lakes High School '18
Beckendorff Junior High '14

jonboyage
Member
Posts: 102
Joined: December 13th, 2016, 8:32 am
State: PA

### Re: Astronomy C

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?
I was in a bin

Rustin '19
UPenn '23

c0c05w311y
Member
Posts: 19
Joined: February 20th, 2017, 7:56 pm
State: PA
Location: Carnegie Mellon University

### Re: Astronomy C

jonboyage
Member
Posts: 102
Joined: December 13th, 2016, 8:32 am
State: PA

### Re: Astronomy C

That's just about correct. Parts E and F were mostly for fun so those answers are acceptable. Your turn!
I was in a bin

Rustin '19
UPenn '23

c0c05w311y
Member
Posts: 19
Joined: February 20th, 2017, 7:56 pm
State: PA
Location: Carnegie Mellon University

### Re: Astronomy C

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
Member
Posts: 486
Joined: January 20th, 2017, 5:02 pm
State: CA

### Re: Astronomy C

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?
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.
2018 Events
2019 Events
--
West High '19
UC Berkeley '23

c0c05w311y
Member
Posts: 19
Joined: February 20th, 2017, 7:56 pm
State: PA
Location: Carnegie Mellon University

### Re: Astronomy C

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?
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.

Unome
Moderator
Posts: 4085
Joined: January 26th, 2014, 12:48 pm
State: GA
Location: somewhere in the sciolyverse

### Re: Astronomy C

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?
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.

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).
Userpage
Chattahoochee High School Class of 2018
Georgia Tech Class of 2022

Opinions expressed on this site are not official; the only place for official rules changes and FAQs is soinc.org.

PM2017
Member
Posts: 486
Joined: January 20th, 2017, 5:02 pm
State: CA

### Re: Astronomy C

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?
2018 Events
2019 Events
--
West High '19
UC Berkeley '23

jonboyage
Member
Posts: 102
Joined: December 13th, 2016, 8:32 am
State: PA

### Re: Astronomy C

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
I was in a bin

Rustin '19
UPenn '23

PM2017
Member
Posts: 486
Joined: January 20th, 2017, 5:02 pm
State: CA

### Re: Astronomy C

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.)

3) I am the first known radio-quiet pulsar. Who am I?
b. What is my rotational period?
c. If I was 1 parsec away from the earth, what would my apparent magnitude be?
2018 Events
2019 Events
--
West High '19
UC Berkeley '23

c0c05w311y
Member
Posts: 19
Joined: February 20th, 2017, 7:56 pm