Astronomy C

[mathemaniac]

In preparation for States, my partner and I just went through the Northview Invite on the Test Exchange. Going through, we found some mistakes and had a couple of questions for the forum as well...

Possible Mistakes:
1. I'm almost positive that 1a. isn't Arcturus; it's Antares. Previous posts on this forum seem to confirm that.
2. A couple of the formulas on the SciOly formula sheet seem incorrect. The "Luminosity of Star" formula which is supposed to be derived from the Stefan-Boltzmann equation doesn't have the correct powers on R and T. Also, "Kepler's 3rd Law" is sort of weird because there should be a "proportional to" sign, not an "=" sign - for a binary star system (which is what this event would most probably use it for), you need the combined mass term in there as well.

Questions:
3. Question "i." in the Short Answer section says that pulsars emit radiation most strongly in the Radio wavelength band; however, in Donna Young's Astronomy webinar, she seems to put a focus on the fact that pulsars are stronger x-ray sources. I did some research into this, and I think the test is right (PSR apparantly stands for "Pulsating Source of Radio"), but I just wanted to check with people here - do pulsars emit more strongly in Radio or X-Ray?
4. In question 4c, when they ask "Why might this number not be what you expect?," are they just going for the small difference in apparant magnitude from the sun or are they going for why that difference is so small? Why is the difference so small?
5. Can someone explain why the answer to 5b is "reddening" (by which I assume it means redshift)? I'm not quite getting why redshift would depress the distance.

Thanks in advance!

[syo_astro]

Yeah, I noticed that mistake and mentioned it earlier. Guess it was ignored XD. I find that the formula sheet should be a working off point. It's good you are researching it and understand the formulas. It's best to have your own organization that works for you. Also, I don't know who made it. I think mistakes were already pointed out in it, so definitely research all the formulas on there, and maybe work out problems to think of other questions.

Reddening actually refers to something called interstellar reddening or extinction. Dust can pretty much absorb some blue light and appear more red. DO NOT CONFUSE THIS WITH REDSHIFT. As for the pulsars, but I'm not fully sure myself. This: http://csep10.phys.utk.edu/astr162/lect ... utron.html
seems to say it emits mostly in X-rays, so that confused me too. But I knew it was very well known that pulsars are detected in radio. Also, that was for neutron stars. Pulsars could be different since I think they have a mechanism that emits radio waves, but at the same time I feel like that may not fully apply since they are such similar objects. For your other question about 4c I'm not fully sure myself.

[Cedavis6]

K, so I'm subbing for this event, and I just wanna know if I should know what lines on a spectra will determine what element the star is composed of.
If so, could you give me a chart if possible?

Thank you in advance.

[mathemaniac]

So...after doing a lot of research (including off of this forum), my partner and I haven't been able to find set-in-stone period-luminosity formulas for Type I and Type II Cepheids. There are a slew of different formulas online, almost all of which are different from the ones posted closer to the beginning of this thread, which are all different than the formula "for Type II Cepheids in the J-band."

Does anyone have any ideas or information about this? In all of the tests I've taken where period-luminosity questions have been asked, the formula was provided, but I'm asking just in case it's not.

[AlphaTauri]

K, so I'm subbing for this event, and I just wanna know if I should know what lines on a spectra will determine what element the star is composed of.
If so, could you give me a chart if possible?

Thank you in advance.

Yes, spectral emission/absorption lines will determine what elements are in a star or gas cloud. However, they are VERY difficult to distinguish unless you're given element spectra at the exact same scale as the stellar spectra. Nevertheless, for charts, try:

http://www.ucolick.org/~bolte/AY4_04/lines.gif
http://www1.picturepush.com/photo/a/667 ... us/hnj.png

Something like this may also help distinguish the spectral class of a star: http://media.skyandtelescope.com/images/Spectra_L.jpg

You may also see spectra in this form: http://cas.sdss.org/dr7/en/proj/advance ... ectra1.gif
but the same principle applies - the dips and peaks correspond to various elements that are present.

So...after doing a lot of research (including off of this forum), my partner and I haven't been able to find set-in-stone period-luminosity formulas for Type I and Type II Cepheids. There are a slew of different formulas online, almost all of which are different from the ones posted closer to the beginning of this thread, which are all different than the formula "for Type II Cepheids in the J-band."

Does anyone have any ideas or information about this? In all of the tests I've taken where period-luminosity questions have been asked, the formula was provided, but I'm asking just in case it's not.

There's not really one definitive formula for the P-L relationship, since there's a good deal of scatter in the actual data due to interstellar extinction and other effects. However the best equation I've found - from an astrophysics textbook, no less - is something like -2.81 log(P) - 1.43 for Type I Cepheids, with a +1.5 or +1.6 mag correction for Type II Cepheids. (Also, fyi, the J-band is an infrared band, so that's definitely going to give you different answers than an equation for the visible bands.)

[fourLoko]

Quick Question: For question 73 in the 2012 PA Regionals test the question asks when helium shell burning takes place. I thought this occurred during the subgiant branch but the answer key says it occurs in the AGB. Carrol and Ostile seems to support my choice, is the answer key just wrong or am I being dumb?

[AlphaTauri]

As far as I know, He shell burning occurs on the AGB (source: C/O, p. 458-459, 463 - if the page numbers don't match up between editions, it's Fig 13.4, 13.5, and the section entitled "The Early Asymptotic Giant Branch").

You may have mixed it up with hydrogen shell burning, which does in fact happen on the Subgiant Branch?

[fourLoko]

As far as I know, He shell burning occurs on the AGB (source: C/O, p. 458-459, 463 - if the page numbers don't match up between editions, it's Fig 13.4, 13.5, and the section entitled "The Early Asymptotic Giant Branch").

You may have mixed it up with hydrogen shell burning, which does in fact happen on the Subgiant Branch?

Ohhhh, youre totally right, I guess my brain can't distinguish between H and He, thank you very much

[Asteroidea]

Anyone have the answer sheet to the Mentor Astro Test?

[syo_astro]

Anyone have the answer sheet to the Mentor Astro Test?

Um, what do you mean by Mentor Astro? There is one on the wiki...but if you went to the Mentor invite and got the test, then you should be able to get some sort of answer key or flashdrive with it that has it. Only really other people from the invite would know...maybe try contacting the Mentor team or something?