Astronomy C

[astro124]

Oh I figured it out.

47 Tucanae has a ton of low mass x-ray binary systems, cataclysmic variable stars, white dwarfs, etc. need its center. All those objects are on the list this year!

[islipscioly]

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.

[syo_astro]

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!

[astro124]

What are some equations that you guys suggest for the test? So far I have the following:

Parallax [1/d=p]
Distance Modulus [m-M=5log(d)-5 or m-M=5log(d/10)
Small Angle [angular diameter/206265=linear diameter/d]
Kepler's 3rd Law [MA+MB=a^3/p^2]
Schwarzschild Radius [Sr=2GM/c^2]
Luminosity of Stars (based off of the Stefan-Boltzmann equation) [L/Lsolar=(R/Rsolar)^2*(T/Tsolar)^4
Luminosity-Absolute Magnitude Conversion Equation [4.85-2.5log(Lsolar)]
B-V to Temperature (in Kelvin) conversion equation [T=4600(1/0.92(B-V)+1.7)+(1/0.92(B-V)+0.62)
Rotational Period [2(pi)(r)=v(P)]

Any other equations worth knowing?

[syo_astro]

What are some equations that you guys suggest for the test? So far I have the following:

Parallax [1/d=p]
Distance Modulus [m-M=5log(d)-5 or m-M=5log(d/10)
Small Angle [angular diameter/206265=linear diameter/d]
Kepler's 3rd Law [MA+MB=a^3/p^2]
Schwarzschild Radius [Sr=2GM/c^2]
Luminosity of Stars (based off of the Stefan-Boltzmann equation) [L/Lsolar=(R/Rsolar)^2*(T/Tsolar)^4
Luminosity-Absolute Magnitude Conversion Equation [4.85-2.5log(Lsolar)]
B-V to Temperature (in Kelvin) conversion equation [T=4600(1/0.92(B-V)+1.7)+(1/0.92(B-V)+0.62)
Rotational Period [2(pi)(r)=v(P)]

Any other equations worth knowing?

There's plenty more than that! Have you looked into spectroscopic binaries? Do you have the Stefan-Boltzmann equation? Even Wien's displacement law. Do you know where parallax and the distance modulus come from conceptually so you can prove a full understanding of it on any test? There's plenty you could look for just by looking up astronomy equations and formulas into google. If you find that a bit too vexing, use different objects to find associated equations. We come up with these laws for a good reason (to properly analyze what we see around us). I find that makes the process a bit more fun and provides a good depth to your search. If you don't want to do that, there's certainly the large number of tests available on the test exchange, and the scioly wiki has an equation sheet (though, I can't remember if anyone ever bothered to fix issues on it). Hope that helps!

Also, a question. I've never actually found a proper equation for converting color-index. Where'd you find that one out of curiosity?

[astro124]

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.

[syo_astro]

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.

[islipscioly]

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]

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!

[Crazy Puny Man]

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...