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Re: Astronomy C

Posted: September 22nd, 2016, 5:02 am
by Unome
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?

Re: Astronomy C

Posted: September 22nd, 2016, 2:39 pm
by Magikarpmaster629
@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

Re: Astronomy C

Posted: September 22nd, 2016, 7:23 pm
by slowpoke
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

Re: Astronomy C

Posted: September 27th, 2016, 9:41 pm
by Adi1008
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.

Re: Astronomy C

Posted: October 1st, 2016, 10:00 am
by Magikarpmaster629
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.
Image
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?

Re: Astronomy C

Posted: October 1st, 2016, 11:02 am
by slowpoke
1. NGC 2392
2. 5.87 pc
3. 82051 yrs
4. 4.87 e39 J
5. 274.7 AU, .00545"
6. 103 AU

Re: Astronomy C

Posted: October 1st, 2016, 2:10 pm
by Adi1008
1. NGC 2392
2. 5.87 pc
3. 82051 yrs
4. 4.87 e39 J
5. 274.7 AU, .00545"
6. 103 AU
For what it's worth, I got some different answers. I could be totally wrong though; my math's definitely really rusty! ¯\_(ツ)_/¯
1. NGC 2392
2. [b]0.104 pc[/b]
3. [b]1423.5 years[/b]
4. [b]2.4E39 J[/b]
5. [b]0.00275 AU, 3.13E-6 arcseconds[/b]
6. [b]0.00103 AU[/b]

Re: Astronomy C

Posted: October 1st, 2016, 2:53 pm
by slowpoke
1. NGC 2392
2. 5.87 pc
3. 82051 yrs
4. 4.87 e39 J
5. 274.7 AU, .00545"
6. 103 AU
For what it's worth, I got some different answers. I could be totally wrong though; my math's definitely really rusty! ¯\_(ツ)_/¯
1. NGC 2392
2. [b]0.104 pc[/b]
3. [b]1423.5 years[/b]
4. [b]2.4E39 J[/b]
5. [b]0.00275 AU, 3.13E-6 arcseconds[/b]
6. [b]0.00103 AU[/b]
NVM I am indeed completely wrong. You seem to be right.

Re: Astronomy C

Posted: October 1st, 2016, 4:55 pm
by Magikarpmaster629
1. NGC 2392
2. 5.87 pc
3. 82051 yrs
4. 4.87 e39 J
5. 274.7 AU, .00545"
6. 103 AU
For what it's worth, I got some different answers. I could be totally wrong though; my math's definitely really rusty! ¯\_(ツ)_/¯
1. NGC 2392
2. [b]0.104 pc[/b]
3. [b]1423.5 years[/b]
4. [b]2.4E39 J[/b]
5. [b]0.00275 AU, 3.13E-6 arcseconds[/b]
6. [b]0.00103 AU[/b]
NVM I am indeed completely wrong. You seem to be right.
Adi's right, so it's his turn.

Re: Astronomy C

Posted: October 2nd, 2016, 10:39 am
by Adi1008
Adi's right, so it's his turn.
Also, just some pretty cool stuff about gravitational waves and how they're produced. In any gravitational system, gravitational waves are always being produced, due to a change in the quadrupole moment of the gravitational system. Since the orbit is losing energy this way, if the effect of gravitational waves is significant enough, then the orbit will actually decay. For the Earth - Sun system, for example, the orbit loses about 200W in the form of gravitational waves (which is barely anything, there are other effects that push the Earth out more than gravitational waves pull it in). Gravitational waves are much stronger when they involve objects reallyyyy close together and dense, like short period binary white dwarfs and pulsars (in fact, a pulsar-neutron star binary, PSR B1913+16, provided some of the first indirect evidence for gravitational waves!!).

So to summarize - gravitational waves are always being produced, and that loss of energy is what causes orbits to decay. The effect is much more significant when the objects are dense and close together.

Anyways, here's my problem:
Image

(a) What wavelength is this image taken in, and what telescope took this picture?
(b) What specific object (include A and B designations) is this associated with?
(c) What causes the phenomenon seen in the picture?
(d) This DSO is extremely well known, but this phenomenon was not discovered until very recently. What could explain this?