Astronomy C

[Magikarpmaster629]

Regarding 2MASSJ22282889-431026, there is info on the wiki page giving right ascension/declination etc. Does anyone know where this was found? I'm having a hard time finding any real data on that object, just news stories. I searched in Simbad even and got nothing.

Thanks!

I haven't really found anything concrete about it except for press releases too :/

I found a single abstract on ADS. It looks like weather patterns is pretty much all there is in it.

[arvind_r]

If a planet has an emissivity not equal to 1, then would its equilibrium temperature equal

or do you have to incorporate the epsilon differently?

[syo_astro]

Answering some questions:

1) A hint for the 2MASS object would be for the RA and Dec look at the coordinates and how 2MASS catalogues objects (at least I think, I haven't looked at the DSOs on the wiki as much, sorry).

2) Wouldn't emissivity in that case go on the bottom? At least that's just from what I'm eyeing when equating P_in and P_out (and emissivity comes from the P_out side).

[Skink]

This event is kicking my butt. Being in the physical sciences is no prerequisite for Astro; yikes (do event supervisors actually have the needed background for this generally?)...so, my team's binder is as populated as we could hope for at this point save for section 3.-no-subsection, you know, that list of charts, spectra, and things...we intuitively 'get' light curves. They're flux (or magnitude? Okay, maybe I don't 'get' it...) versus time or whatever. What I have been unable to find is a Spark Notes or For Dummies version, let alone a technical introduction to them. And, while I don't have any on hand, I figure color-color diagrams and multi-wavelength images are intuitive. It's just that they're not (clearly labeled) in the orange book or anywhere else within reach. I've combed through astronomy and astrophysics notes for months for a quick treatment of this stuff. No dice...

On another note, I was amused this morning when checking the recent event FAQs. Really, someone, somewhere, needs extra--external--storage for this event?

[syo_astro]

Hey Skink, it is always good to ask for help on the forums!

I am sorry, but I am a bit confused (maybe other people aren't and just will directly answer everything). Is it that you have problem with all those tools listed that are used in astronomy? Is it something specific, like light curves, or is it everything?

[Skink]

I'm not sure, really; it's hard to gauge that when I can't find cut-and-dry explanations of these 'tools' (versus, say, if you were in a chemistry event and had to learn about different instruments used and the resultant spectra generated by them...that would be a rather easy assignment despite the complexity of the material). Yeah, Wikipedia has a page on light curves and things, but it's often skeletal and devoid of enough examples. Related, consider all of those figures on the National test from last season (if you have it). Where are the event supervisors pulling them from? It's hard to practice reading these graphs and images (many of which are the DSOs, granted) without knowing from where they're coming. It's not hard to find what they are, but SO isn't so interested in what things are but how to use and interpret them. Similarly, then, I can find 'multiwavelength image' explanations; heck, I have one posted on my wall! But, I can't generate practice questions with any of that, especially without new examples on hand. Does that make sense?

[sciolymom]

Question about evolutionary sequence of high mass stars:

Most sources indicate a sequence like this:
main sequence - cepheid variable (which I guess would technically be instability strip of horizontal branch?) - then supergiant. I'm not seeing anything in that sequence about red giant or AGB.

But another source gave this sequence:
• Subgiant Branch (SGB) - hydrogen shell burning - outer layers swell
• Red Giant Branch - helium ash core compresses - increased hydrogen shell burning
• First Dredge Up - expanding atmosphere cools star - stirs carbon, nitrogen and oxygen upward - star heats up
• Core Helium Flash - continued compression with added helium ash ignites helium - lots of neutrinos
• Horizontal Branch - helium burning core - hydrogen burning shell
• Pre AGB (Asymptotic Giant Branch) - outer layers expand cooling the star - hydrogen shell becomes dormant
• AGB - re-ignited hydrogen shell burning (like a second Red Giant phase)
• Several stages of dredge up - nucleosynthesis creates numerous elements (F, Ne, Mg, Al, Li, Ne, Na)

How can a massive star go through the Red Giant branch?? And based on where the Red Giant branch and the AGB are located on the HR diagram, it doesn't *look* like a massive star goes through that area on the diagram. I'm confused! (This came up because we are trying to understand the horizontal and AG branches better).

[syo_astro]

Skink, it makes a lot of sense, but I think you know that it is hard to help without isolating problems. You named a few in that last post that I hope to resolve. Also, I put it as "tools" because as you say it is very much about understanding the USE of these various diagrams. Certain things are confusing, though. For example, I always had trouble doing spectroscopy and how much one had to know about specific spectral lines.

Light curves always plot intensity of light (which if you know astronomy, is aka flux or brightness or our crazy magnitude system) vs. time. What does it mean? You should see that stars/pre-main seq stars change their light output over time. But why? The answer is...variable, so to say. There are MANY reasons for this changing light output, and it shows how simple observations give a physical understanding of some object. There are technical terms here, like intrinsic, extrinsic, etc, etc, but we need to put it in context like you say. About exoplanets + young stars, where do we see variability? If we look up the light curve for each type of object we see patterns. Like if you do it for a brown dwarf, T Tauri, Herbig Ae/Be star, and some exoplanet-y ones (namely transit light curves). With that, given any light curve you should simply know it from the pattern and what causes that pattern (superficially).

If you look at specific DSOs, then you'll better understand what they are and how we know what they're doing physically based on the light curve. You can get these images from many sources. From google (I recommend checking the web page to make sure the image goes with the object you searched for), or better Hubble/Chandra/Spitzer/AAVSO work well. I mean, even for multi-wavelength images, the DSOs have tons online sometimes from papers too that act as good sources for questions. Sorry that there is no magic answer, but if you go between finding images for DSOs and finding images for random objects, you should get why the multi-wavelength images are different or why the light curves have their pattern or lack of one. I myself have googled "T Tauri light curve" or "brown dwarf light curve". Are you not able to find key features when you look them up? Typically they are listed, especially on AAVSO. But this is just one useful diagram.

I have two main points: The event gives you free examples if you can't find any (the DSOs, though you should find random general examples as backup if you google say "object" + "light curve"), and actually having an understanding of a physical basis behind the different tools, features, and images helps you to understand why they look the way they do. I hope that helps to some extent, and if you have more questions please ask.

Remember if you run out of practice, there are tests on the test exchange for astro, and part of the rules tends to not change much (okay, except the color-color diagrams thing...but it's very appropriate for pre-main sequence stars, I promise). Another resource is also the question marathons, which hey make this forum as active as possible!

On a side note about the images on last year's national exam. I am curious which ones you found to seem tough to come up with as an example (here it is for ref: https://www.aavso.org/sites/default/fil ... Images.pdf). I guess I am biased, but I don't see question writing as so complex because for me it was always just like studying in reverse. In studying I would amass large quantities of information, systematically organize it, and understand the scientific connections so I could say discuss about it. In question writing I do the same information amassing, but I ask for someone to tell me about it leaving out a few key bits that reflect understanding or require putting together the information.

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Now for sciolymom...I feel bad if people ask about high mass stellar evo when that's not really the emphasis. I can answer you question pretty directly, though. High-mass stars follow different post-main sequence tracks from low-mass stars that follow the track you discussed with the RGB and all. Where did it say high-mass stars go through those evolutionary steps? Here's a neat little table from wiki that might help to summarize how high-mass is quite different: https://en.wikipedia.org/wiki/Wolf%E2%8 ... ent_models (by schematic evolution...).

[sciolymom]

SYO, this was the link. Actually, the first one that came up under high mass star evolution. It sounded off to me, that is why I wanted to clarify.
http://astronomyonline.org/Stars/HighMassEvolution.asp

Stellar evolution is part of the topic, no?
"stellar evolution and star formation and exoplanets"
We aren't spending a ton of time on it, just brushing up. We were looking at what tracks different things follow on the HR diagram.

[syo_astro]

Stellar evolution is DEFINITELY a part of the event, but that's not what I mean. The event at least in my perspective focuses on stellar evolution in conjunction with the other topics, so it should emphasize pre-main sequence evolution and understanding of planets. Admittedly, I have seen many tests ask about some general stuff as you are studying, so it is what it is. Also, for sure if one is interested in the topic it never hurts, it's quite fun!

I think http://casswww.ucsd.edu/archive/physics ... ass_ev.pdf would serve as a better summary. It's longer, slightly more detailed, and gives details in case you want to search more up about parts of the evolution. Or if you just look up "high mass stellar evolution" on google you'll find more sources. It's funny because I remember using astronomyonline when starting out...but mistakes are mistakes, certainly good to ask.