Astronomy C

astro124
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Re: Astronomy C

Postby astro124 » February 17th, 2014, 5:14 pm

I guess you're right! I'm trying to nail the basic ones first before I start hitting the more complex equations. Plus I still have the conceptual stuff to get down (I know most but I need a good refresher).

As for the Stefan Boltzmann law, I thought the luminosity of stars equation (L/Lsolar=(R/Rsolar)^2*(T/Tsolar)^4) was derived from that. I've been trying to figure out the Boltzmann equation since last year (L = 4π σ R² T⁴) but the Boltzmann constant doesn't make any sense to me. So instead I've been using the first equation.

I honestly don't know Wien's Law. Like flux it's on my bucket list of stuff to get down, but like I said I have concepts to get down. Could you possibly explain it to me?

Oh, and finally for the B-V index equation. I was looking around on Wikipedia and followed a link to one of the external sources. It's only an approximation but it's better than nothing.
2012 Season: Reach for the Stars-3rd (State) / Keep the Heat-19th (State)
2013 Season: Astronomy-2nd (State) / Disease Detectives-15th (State)
2014 Season: Astronomy-1st (State) / Experimental Design-20th (State)/ Anatomy and Physiology-16th (State)
2015 Season: Astronomy

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syo_astro
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Re: Astronomy C

Postby syo_astro » February 17th, 2014, 5:27 pm

I guess you're right! I'm trying to nail the basic ones first before I start hitting the more complex equations. Plus I still have the conceptual stuff to get down (I know most but I need a good refresher).

As for the Stefan Boltzmann law, I thought the luminosity of stars equation (L/Lsolar=(R/Rsolar)^2*(T/Tsolar)^4) was derived from that. I've been trying to figure out the Boltzmann equation since last year (L = 4π σ R² T⁴) but the Boltzmann constant doesn't make any sense to me. So instead I've been using the first equation.

I honestly don't know Wien's Law. Like flux it's on my bucket list of stuff to get down, but like I said I have concepts to get down. Could you possibly explain it to me?

Oh, and finally for the B-V index equation. I was looking around on Wikipedia and followed a link to one of the external sources. It's only an approximation but it's better than nothing.
Yeah, I don't feel like finding a quote, but I feel like many people could say that a whole life can be spent mastering the basics or something.

The Stefan-Boltzmann law is basically that, though you could theoretically factor in the constant for emissivity (for blackbodies it's one, that's why it's left out for us). What's the problem with the Boltzmann constant?

Wien's law basically says that temperature times maximum emitted wavelength is equal to a constant. It's fundamentally a way of figuring out a star's effective temperature I believe. I think it's T=b/lambda[max], where T is in Kelvin, b is 2.9x10^6 K*nm, lambda max is in nm in this case (have to make sure you're units are consistent). What's the issue there? Flux itself I can say can be kinda annoying to learn at first. Think of it like intensity or brightness of light instead of the flux of light, and maybe that can help. You know that the intensity of light hitting your eye from a light source further away would decrease because that light source would be "less bright" (the energy covered in the same surface area further away would decrease). This is explained in the equation F=L/(4pir^2) or luminosity per surface area essentially (since light spreads out in this way), with units usually of W/m^2. Any problems there?

Thanks for the B-V thing! Didn't realize wikipedia updated, last time I checked I didn't see that there XD. Yeah, there's a conceptual basis I'd think to even explain that too.
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islipscioly
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Re: Astronomy C

Postby islipscioly » February 17th, 2014, 10:58 pm

As the NYS Astronomy event writer for States, I aim to ensure that the students have a comprehensive knowledge of the topics highlighted in the rules manual, including the related equations. The DSOs were present on last year's exam with questions related to the DSOs. It is not merely an identify question and move on. They will reappear on this year's exam, as DSOs are a portion of the exam. You can be given information (charts, graphs, images, etc.) about other objects besides the DSOs and be asked to answer questions related to part A and B of the rules, as the focus of this year's exam is stellar evolution and variable stars. I find that many teams merely focus on the DSOs and forget about the essence of the event: astronomy. But I can assure you that when I write exams, the rules are next to me and I make every effort to ensure that the questions are related to the event parameters.
Well, if people are studying only their DSOs I at least hope to be up to the challenge of states ;). Sorry if I only comment on stuff that annoys me (like there were definitely some good questions on Betelgeuse and had to really know your way around binaries iirc...for sure wasn't saying there were NO DSOs). Hope to see you there and whatnot, definitely good luck to Islip!
Oh no worries. I just wanted to clarify if anyone chose not to study the DSOs, as there will be questions on them and the related concepts to Part A and Part B. With last year under my belt and writing for the Islip Invy and Regionals this year, I hope to have finally gotten this exam writing thing down. Hopefully you will enjoy in a few weeks. I'll be there on Friday night at Kellenberg. It'll be nice this year with the team qualifying and all. Good luck with your preparations! I'd like to hear your feedback afterwards (too specific/too general/etc.) so I can continue to improve for the future.

astro124
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Re: Astronomy C

Postby astro124 » February 20th, 2014, 6:46 am

So about Type II supernova remnants.....

Let's say that a star goes through a type II supernova, and the result is a stellar mass black hole. Would there be any remnant left behind? My thought is that the answer is 'no' because isn't the remnant produced when the outer layers of the star implode and then bounce off the surface of the neutron star? Wouldn't a black hole just consume anything that was left behind?

Also, about Cepheid distances. I think I have this locked down, but just to clarify. In order to calculate distances to a Cepheid you would have to look at its light curve and from that you can determine its period and mean apparent magnitude. From there you then take its period and either enter it into a Luminosity-Period chart to find an approximation of its absolute magnitude (some charts are in solar luminosity so you would have to convert) or you use an equation like: Mv=-2.78log(p)-1.35 or Mv=-2.81log(p)-1.43 (these equations should get you roughly the same answer). Finally, you enter it into distance modulus and solve for 'd' in parsecs.

Finally, how about RR Lyrae and 1a supernovae. For RR Lyrae, isn't the process roughly the same? You look at a light curve to determine the period and mean apparent magnitude, but then what? Does anybody have a P-L equation for Lyrae or a good approximation graph like the millions available for Cepheid stars? And then what about calculating distances to Type 1a supernova?. How good is trying to calculate the distance to a cataclysmic variable, anyways? I've been looking and online sources have been telling me that they're great for distance calculation but none of them have provided a method for solving for the distance?

Thanks for the help!
2012 Season: Reach for the Stars-3rd (State) / Keep the Heat-19th (State)
2013 Season: Astronomy-2nd (State) / Disease Detectives-15th (State)
2014 Season: Astronomy-1st (State) / Experimental Design-20th (State)/ Anatomy and Physiology-16th (State)
2015 Season: Astronomy

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Crazy Puny Man
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Re: Astronomy C

Postby Crazy Puny Man » February 20th, 2014, 7:07 am

So about Type II supernova remnants.....

Let's say that a star goes through a type II supernova, and the result is a stellar mass black hole. Would there be any remnant left behind? My thought is that the answer is 'no' because isn't the remnant produced when the outer layers of the star implode and then bounce off the surface of the neutron star? Wouldn't a black hole just consume anything that was left behind?

Also, about Cepheid distances. I think I have this locked down, but just to clarify. In order to calculate distances to a Cepheid you would have to look at its light curve and from that you can determine its period and mean apparent magnitude. From there you then take its period and either enter it into a Luminosity-Period chart to find an approximation of its absolute magnitude (some charts are in solar luminosity so you would have to convert) or you use an equation like: Mv=-2.78log(p)-1.35 or Mv=-2.81log(p)-1.43 (these equations should get you roughly the same answer). Finally, you enter it into distance modulus and solve for 'd' in parsecs.

Finally, how about RR Lyrae and 1a supernovae. For RR Lyrae, isn't the process roughly the same? You look at a light curve to determine the period and mean apparent magnitude, but then what? Does anybody have a P-L equation for Lyrae or a good approximation graph like the millions available for Cepheid stars? And then what about calculating distances to Type 1a supernova?. How good is trying to calculate the distance to a cataclysmic variable, anyways? I've been looking and online sources have been telling me that they're great for distance calculation but none of them have provided a method for solving for the distance?

Thanks for the help!
I'm pretty sure that, for your first question, the remnant is the black hole itself

Your explanation on Cepheids is correct. RR Lyrae stars have an average absolute magnitude of about +0.75 regardless of their period; so you just take their mean apparent magnitude and use the distance modulus from there. For Type Ia supernova, the peak absolute magnitude is always -19.3. You simply need to find the apparent magnitude at its peak and go from there.

Not sure about anything with cataclysmic variables... :?:

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Re: Astronomy C

Postby syo_astro » February 20th, 2014, 11:36 am

Then tell me how that would explain the case of w49b ;). I mean if I understand your question to mean whether there's an SNR (like the large cloud of colorful ejecta you see with many supernovae ). It is also true that a black hole is an "SNR" since it is a remnant...from a supernova. It actually depends on what you're taking about, but assuming it's not a collapsar like cygnus x-1 have you taken a look at w49b. Hopefully I understood your question.

As for rr lyrae and type ia SNe I'll agree, there's a plus or minus for those values but what's said is fine. I would say oh what if they give you solar luminosities or something but from your equations sounds like you know how to handle that. There's also a way to use novae as standard candles but I've never found a question on it or where it was used exactly. Other supernovae can be used as sorts of standard candles iirc. Light echo calculations and correlations I think have been used to try to figure that out. But hands down knowing rr lyrae, cepheids, type ia are most useful.

Any specific problems with this or the equations stuff from before?
B: Crave the Wave, Environmental Chemistry, Robo-Cross, Meteorology, Physical Science Lab, Solar System, DyPlan (E and V), Shock Value
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astro124
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Re: Astronomy C

Postby astro124 » February 20th, 2014, 5:15 pm

Yeah, the ejecta wave that often comes with most supernovae is what I was asking about. I wanted to see if it was possible for a black hole to have an ejecta wave round it. As for W49B, I thought read somewhere that some of the clouds and interstellar debris existed before the star went supernova (and isn't only theorized that there is a black hole).

As for the process of a Type II supernova, am I correct? Does the core collapse, followed by the outer envelope of the star imploding in on itself, to later then bounce of the neutron star and create the shockwave? I remember seeing this question last year on the Astro state test for Arizona, and I was pretty confident with my answer (also, it was the only one that made sense).

Finally, by collapsar do you mean a star (over 40-50 solar masses) that collapses directly into a black hole without a supernova event?
2012 Season: Reach for the Stars-3rd (State) / Keep the Heat-19th (State)
2013 Season: Astronomy-2nd (State) / Disease Detectives-15th (State)
2014 Season: Astronomy-1st (State) / Experimental Design-20th (State)/ Anatomy and Physiology-16th (State)
2015 Season: Astronomy

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Re: Astronomy C

Postby syo_astro » February 20th, 2014, 9:08 pm

Yeah, the ejecta wave that often comes with most supernovae is what I was asking about. I wanted to see if it was possible for a black hole to have an ejecta wave round it. As for W49B, I thought read somewhere that some of the clouds and interstellar debris existed before the star went supernova (and isn't only theorized that there is a black hole).

As for the process of a Type II supernova, am I correct? Does the core collapse, followed by the outer envelope of the star imploding in on itself, to later then bounce of the neutron star and create the shockwave? I remember seeing this question last year on the Astro state test for Arizona, and I was pretty confident with my answer (also, it was the only one that made sense).

Finally, by collapsar do you mean a star (over 40-50 solar masses) that collapses directly into a black hole without a supernova event?
For W49B I was just pointing out an example that's kinda relevant (you did mention a black hole with a massive explosion, closest DSO that's relevant this year :P). Also, as far as theories go, this was a "careful search done", it's decently likely. I'd like to see hints of a plerion or something more closely associated to a neutron star personally, a black hole is decently possible. I could say we only speak in theory, it's only "theorized" how supernovae mechanisms work (don't mean too sound defensive/argumentative, hope you know what I mean). You sure on the surrounding ejecta? I thought that was just one of a few theories, and the bipolar jet one that seemed unusual ended up being more likely. I am curious why our info conflicts there (I could very well be reading incorrectly, sorry if I am).

I think the theory behind how supernova remnants are left behind is slightly complex...One explanation to my understanding that I looked up to check (wow I didn't know neutron stars could be compressed this much!) is that the implosion occurs and then this pushes onto the neutron star until it's so dense you get an explosion. I think the point was basically you're right as far as a rebound with the neutron star goes, but to add:
However, the rebound is only part of the mechanism by which the supernova generates its energy. The binding energy of a neutron star is much less than that of a non-collapsed stellar core. The tremendous amount of energy generated by the neutron star formation drives the supernova. The same is true with the formation of a black hole, save that the binding energy of the black hole is even less than a neutron star and hence the explosion would be somewhat more energetic. So the formation to a black hole still includes an explosion.
An example does exist though, a black hole with an SNR would be SS433 and W50 (it's quite awesome, just saying :D).

By collapsar I was just discussing an example possibly by what you mean, where there wasn't exactly a remnant left behind, but we know there also possibly wasn't a supernova (Cyg X-1 if you recall from last year is a fairly major example of this).

Phew, that help clear some things up?
B: Crave the Wave, Environmental Chemistry, Robo-Cross, Meteorology, Physical Science Lab, Solar System, DyPlan (E and V), Shock Value
C: Microbe Mission, DyPlan (Earth's Fresh Waters), Fermi Questions, GeoMaps, Gravity Vehicle, Scrambler, Rocks, Astronomy
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astro124
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Re: Astronomy C

Postby astro124 » February 20th, 2014, 9:30 pm

Yeah, that really helped! Thanks a lot! Do you have a link to the source where you got your information. I want to try and make sure I have that stuff in my notes this year, since you never know what might be asked.

Also, would you mind taking a look at my DSO catalog?
2012 Season: Reach for the Stars-3rd (State) / Keep the Heat-19th (State)
2013 Season: Astronomy-2nd (State) / Disease Detectives-15th (State)
2014 Season: Astronomy-1st (State) / Experimental Design-20th (State)/ Anatomy and Physiology-16th (State)
2015 Season: Astronomy

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syo_astro
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Re: Astronomy C

Postby syo_astro » February 20th, 2014, 9:36 pm

Yeah, that really helped! Thanks a lot! Do you have a link to the source where you got your information. I want to try and make sure I have that stuff in my notes this year, since you never know what might be asked.

Also, would you mind taking a look at my DSO catalog?
http://imagine.gsfc.nasa.gov/docs/ask_a ... 0215d.html. That's what I basically had for the supernova rebound. For W49B and the other objects...I mean, those I looked at multiple papers and chandra to assess, so I'd rather not have to link all of it unless you can't find it?

ALSO WOAH, YOU ALREADY HAVE A CATALOG, WHAT'S THE NAME (okay, sorry couldn't help it, ie. Messier, NGC, IC XD)? I'm a bit busy prepping for states myself, but I like to help. I'll try to take a look, how do you want me to (PM, email, PM asking for my email, I guess something along those lines)?
B: Crave the Wave, Environmental Chemistry, Robo-Cross, Meteorology, Physical Science Lab, Solar System, DyPlan (E and V), Shock Value
C: Microbe Mission, DyPlan (Earth's Fresh Waters), Fermi Questions, GeoMaps, Gravity Vehicle, Scrambler, Rocks, Astronomy
Grad: Writing Tests/Supervising (NY/MI)


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