## Astronomy C

Test your knowledge of various Science Olympiad events.
Moderator
Posts: 473
Joined: December 6th, 2013, 1:56 pm
State: TX
Location: Austin, Texas

### Re: Astronomy C

(sorry for the late post!)

Consider the graph below, which shows two quantities for a white dwarf, mass and density, plotted as a function of radius. X-values increase going to the right, and y-values increase going up.

(a) Which colored line shows the mass?
(b) Which colored line shows the density?
(c) What does this graph suggest about the relationship between mass and radius for this type of star?
(d) Is your answer to (c) also true for main-sequence stars?
a) Black
b) Red
c) There is an inverse relationship between mass and radius
d) No; they have a direct relationship
University of Texas at Austin '22
Seven Lakes High School '18
Beckendorff Junior High '14

Magikarpmaster629
Exalted Member
Posts: 578
Joined: October 7th, 2014, 3:03 pm
State: MA
Location: No idea, but I can tell you exactly how fast I'm going

### Re: Astronomy C

DSO fun time!

This is an image of a system that consists of a red giant and a white dwarf.
a) What is the name of this DSO?
b) This DSO is a prototype of what type of variable star? This type is a subcategory of what class of periodic variables?
c) What type of binary system is this DSO in?

A wild goose flies over a pond, leaving behind a voice in the wind.
A man passes through this world, leaving behind a name.

Moderator
Posts: 473
Joined: December 6th, 2013, 1:56 pm
State: TX
Location: Austin, Texas

### Re: Astronomy C

DSO fun time!

This is an image of a system that consists of a red giant and a white dwarf.
a) What is the name of this DSO?
b) This DSO is a prototype of what type of variable star? This type is a subcategory of what class of periodic variables?
c) What type of binary system is this DSO in?
```a. Omricon Ceti (Mira)
b. Mira Variable, Long period variable(?)
c. Semi-detached binary system(?)```
University of Texas at Austin '22
Seven Lakes High School '18
Beckendorff Junior High '14

Magikarpmaster629
Exalted Member
Posts: 578
Joined: October 7th, 2014, 3:03 pm
State: MA
Location: No idea, but I can tell you exactly how fast I'm going

### Re: Astronomy C

DSO fun time!

This is an image of a system that consists of a red giant and a white dwarf.
a) What is the name of this DSO?
b) This DSO is a prototype of what type of variable star? This type is a subcategory of what class of periodic variables?
c) What type of binary system is this DSO in?
```a. Omricon Ceti (Mira)
b. Mira Variable, Long period variable(?)
c. Semi-detached binary system(?)```
I guess I was kinda vague on b and c. I was looking for 'symbiotic binary' on b but semi-detached works too. Your turn.

A wild goose flies over a pond, leaving behind a voice in the wind.
A man passes through this world, leaving behind a name.

Moderator
Posts: 473
Joined: December 6th, 2013, 1:56 pm
State: TX
Location: Austin, Texas

### Re: Astronomy C

DSO fun time!

This is an image of a system that consists of a red giant and a white dwarf.
a) What is the name of this DSO?
b) This DSO is a prototype of what type of variable star? This type is a subcategory of what class of periodic variables?
c) What type of binary system is this DSO in?
```a. Omricon Ceti (Mira)
b. Mira Variable, Long period variable(?)
c. Semi-detached binary system(?)```
I guess I was kinda vague on b and c. I was looking for 'symbiotic binary' on b but semi-detached works too. Your turn.
Could you explain how "symbiotic binary" would be a possible answer choice for (b)? (or did you mean (c), in which case, what would you put for (b)?)

Anyways, here's my question: A team of astronomer catalogs a Star A as a subdwarf. 20 years later, after carefully analyzing this star's movement through the sky, another team of astronomers notices that the proper motion of this star is unusually high.

(a) What does this imply about the distance to Star A?
(b) Briefly describe explain how the new evidence about Star A's proper motion could be used as evidence that it is, in actuality, a white dwarf as opposed to a subgiant star

Everybody's really excited about this new discovery, which launches even more in depth observations of the system!! They soon discover that Star A is actually composed of two white dwarfs, X and Y, having the radial velocity chart below:

(c) Suppose that X is the more massive star. Which colored line shows it's radial velocity?
(d) Going from phase = 0.0 to phase = 2.0 represents how many orbits?
(e) Suppose that the period of these two stars decreases. What type of wave (which LIGO detected evidence for) is produced as a result of this?
(f) Before the astronomers discovered that the Star A was a binary system, they used parallax to estimate that its distance from Earth was d1. Using parallax once again, they estimate the distance to this system, taking into account that it's a binary star system, coming up with a new distance d2. Which of the two distances is bigger?
(f) The combined mass of these two stars is about 0.9 solar masses, which isn't massive enough to result in a Type Ia supernovae. Instead, when the two merge, what type of star will they form?
University of Texas at Austin '22
Seven Lakes High School '18
Beckendorff Junior High '14

Unome
Moderator
Posts: 4105
Joined: January 26th, 2014, 12:48 pm
State: GA
Location: somewhere in the sciolyverse

### Re: Astronomy C

```b) something about lower mass causing an increase in velocity in some direction, idk
c) Blue
d) 2 orbits?
f the second) Another white dwarf?```
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.

Magikarpmaster629
Exalted Member
Posts: 578
Joined: October 7th, 2014, 3:03 pm
State: MA
Location: No idea, but I can tell you exactly how fast I'm going

### Re: Astronomy C

@Adi1008 I don't even remember which one it was supposed to be- symbiotic binaries are both a type of variable star and a type of binary system. It shouldn't matter much.

It looks like all of your answers are right, Unome. As for the rest of them: a) although proper motion doesn't constrain the distance to the star, the distance is probably relatively small
b) I'm really confused on what you mean...first you call it a subdwarf, then in this question a subgiant, and when you mention it could be a white dwarf I think you mean binary star?
c) yep, B, since it has a lower amplitude
d) yep, 2
e) this is a bit of a guess, but d2 should be larger because the parallax angle would be larger in d1 since it didn't account for the star's binary motion
f) yep, they'd merge into a single white dwarf

A wild goose flies over a pond, leaving behind a voice in the wind.
A man passes through this world, leaving behind a name.

slowpoke
Member
Posts: 21
Joined: May 3rd, 2016, 4:59 pm
State: TX

### Re: Astronomy C

`I believe the idea here is that the luminosity was believed to be very high at first, but with the distance being much smaller, the star is actually dimmer and more likely a white dwarf`
2017 R/S/N
Astronomy - 1/1/2
Chem Lab - 4/2/5
Hovercraft - 2/1/7
Materials Science - x/2/1

William P. Clements HS '17

Moderator
Posts: 473
Joined: December 6th, 2013, 1:56 pm
State: TX
Location: Austin, Texas

### Re: Astronomy C

That question was pretty poorly done as a whole, both in terms of wording and content. I'll clarify some stuff and say what I think, at least, are the best answers

(a)While it's true that propler motion isn't really a direct indicator of a star's distance, if it has a very high proper motion, it's more likely that it's closer to Earth than it's moving through space incredibly fast. As a result, you could say that the star is more likely to be closer.
(b) @Magikarp - in the beginning, it's supposed to be subdwarf both times. I think I put subgiant because the answer I was looking for to the second (f) is a type of subgiant star. Anyways, slowpoke's answer to this is essentially perfect; it was exactly what I was looking for. I can't explain it better than he did.
(c) X is more massive, so to conserve momentum it has to be moving slower than the less massive star (recall that in this case, m1v1=m2v2, just like with exoplanets last year!!). Velocity is on the y axis, so having a small amplitude means having a lower velocity. As a result, it has to be blue.
(d) This question's pretty much just asking how many wavelengths are present from phase = 0 to 2, so the answer is 2.
(e) I don't think anyone answered this, but I was looking for gravitational waves. Admittedly, I'm not really sure about how the gravitational waves/white dwarfs orbiting stuff works, so it's possible the question I asked was wrong to begin with. Just for clarification, does the orbit of a binary white dwarf system get smaller because of gravitational waves are emitted, or are gravitational waves being emitted because the orbit get get smaller?
(f#1) Magikarp's answer to this is pretty spot on too! I can't put it better myself.
(f#2) This is another question I'm not really 100% about, because I can't really find much about merging white dwarfs below the Chandrasekhar Limit. The answer I was looking for was actually an R Coronae Borealis star, but I don't really understand the mechanics of merging white dwarfs that well anyways. For all I know, a higher mass white dwarf could be correct as well, Unome and Magikarp have said.
University of Texas at Austin '22
Seven Lakes High School '18
Beckendorff Junior High '14

Magikarpmaster629
Exalted Member
Posts: 578
Joined: October 7th, 2014, 3:03 pm
State: MA
Location: No idea, but I can tell you exactly how fast I'm going

### Re: Astronomy C

I think gravitational waves come from the orbit of the system, not the other way around. If syo_astro sees this, could he please chime in?

Anyway:

The following image contains a DSO. This DSO is a planetary nebula with an angular diameter of 48” and a distance of 880 parsecs.

1) What is the name of this DSO?
2) What is the radius of this nebula in parsecs?
3) If this DSO has an expansion velocity of 70 km/s, what is its age?
4) Although this is quite far from the truth, suppose for a minute that this nebula arose from a single explosion, and that the total expanding mass is 0.5 solar masses. Assuming all parts of the nebula are expanding at the same velocity and that there is no acceleration, what was the total energy of the blast in Joules?
A team of astronomers takes images of this planetary nebula with the Chandra X-ray Space Telescope and discover a binary white dwarf system in its center! This system has a period of one hour and a total mass of 1.6 solar masses.
5) What is the semi-major axis in AU and the angular size in arcseconds of the orbit?
6) If one of the white dwarfs has a mass of 1 solar mass, what is its distance to the barycenter in AU?