## Astronomy C

jonboyage
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### Re: Astronomy C

PM2017 wrote:
ashucha wrote:This may be a bit too specific but does anybody know what the apparent and absolute magnitude of DEM L241 (aka NGC 2029) is and where you got this information? Thanks!

This isn't anywhere close to perfect, but perhaps it's a reasonable estimate.

This paper says that the x-ray source has a luminosity $\approx 2 \times 10^{35} \mathrm{erg/s} = 2 \times 10^{28} \mathrm{W}$ . Converting that to absolute magnitude gives about 0.54

The same paper also mentions that the distance is about 50 kpc. Using the distance modulus, this gives an apparent magnitude of about 19.03

As for the entire remnant, Table 5 in the paper says that it has a luminosity of about $\approx 9.14 \times 10^{35} \mathrm{erg/s} = 9.14 \times 10^{28} \mathrm{W}$ . This would give an absolute magnitude of about -1.11 and apparent magnitude 17.385

Correct me if I'm wrong, but simbad seems to give an apparent magnitude of 12.29.

this would imply an absolute magnitude of -6.20, using the distance modulus (with d= 50,000 pc, from the aforementioned paper)

I would tend to believe PM2017 because later in the paper it says, "The bright optical counterpart, a V = 13.5 O5III(f) star, is
easily visible within the Head of the remnant." The star probably emits a lot of ionizing radiation and lights up, so-to-speak, the rest of the nebula. Note that SIMBAD lists the magnitude in the J band, which is infrared, so that makes sense.
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PM2017
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### Re: Astronomy C

jonboyage wrote:
PM2017 wrote:
Adi1008 wrote:This isn't anywhere close to perfect, but perhaps it's a reasonable estimate.

This paper says that the x-ray source has a luminosity $\approx 2 \times 10^{35} \mathrm{erg/s} = 2 \times 10^{28} \mathrm{W}$ . Converting that to absolute magnitude gives about 0.54

The same paper also mentions that the distance is about 50 kpc. Using the distance modulus, this gives an apparent magnitude of about 19.03

As for the entire remnant, Table 5 in the paper says that it has a luminosity of about $\approx 9.14 \times 10^{35} \mathrm{erg/s} = 9.14 \times 10^{28} \mathrm{W}$ . This would give an absolute magnitude of about -1.11 and apparent magnitude 17.385

Correct me if I'm wrong, but simbad seems to give an apparent magnitude of 12.29.

this would imply an absolute magnitude of -6.20, using the distance modulus (with d= 50,000 pc, from the aforementioned paper)

I would tend to believe PM2017 because later in the paper it says, "The bright optical counterpart, a V = 13.5 O5III(f) star, is
easily visible within the Head of the remnant." The star probably emits a lot of ionizing radiation and lights up, so-to-speak, the rest of the nebula. Note that SIMBAD lists the magnitude in the J band, which is infrared, so that makes sense.

Also the fact that Wikipedia uses SIMBAD as a source, so many test-makers will expect that value.
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### Re: Astronomy C

PM2017 wrote:
jonboyage wrote:
PM2017 wrote:
Correct me if I'm wrong, but simbad seems to give an apparent magnitude of 12.29.

this would imply an absolute magnitude of -6.20, using the distance modulus (with d= 50,000 pc, from the aforementioned paper)

I would tend to believe PM2017 because later in the paper it says, "The bright optical counterpart, a V = 13.5 O5III(f) star, is
easily visible within the Head of the remnant." The star probably emits a lot of ionizing radiation and lights up, so-to-speak, the rest of the nebula. Note that SIMBAD lists the magnitude in the J band, which is infrared, so that makes sense.

Also the fact that Wikipedia uses SIMBAD as a source, so many test-makers will expect that value.

Looks like I was completely wrong then xD

jonboyage and PM2017's stuff seems much more reasonable
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syo_astro
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### Re: Astronomy C

Welp, my internet was bad and post got deleted...so I'll try to summarize before internet goes out...

Adi: That sucks, happens to me too. Would be careful about the paper and other papers because it seems to focus a lot on the X-ray spectrum (and even calls the luminosity "Lx"). While paper reading can help, interpreting the results and data yourself can be a dangerous endeavor, tread carefully. I leave the rest to you all;).

Others: Not sure about that app. mag...no reference seems to be listed, but I guess maybe lots would be satisfied stopping there (though, if you want, feel free to dig deeper!...I won't right now). Question then: Do many test writers ask to give an app. mag. for a random DSO or to calculate the abs. mag for a random DSO (showing work or something)? It's a bit of an odd question, but I got my share of odd questions when I competed. I wouldn't be too surprised.

Fun fact: Alpha, me, someone from Troy I didn't get to see were at an astro conference! It's the American Astronomical Society / AAS conference, and we all presented our research:). Sadly, didn't take a look at many of the black holes / compact objects talks...that said, I should probably get test writing for everyone ASAP >.<.
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### Re: Astronomy C

How would you solve for period in this problem?
https://m.imgur.com/a/GHEO3

Unome
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### Re: Astronomy C

themightyweeaboo wrote:How would you solve for period in this problem?
https://m.imgur.com/a/GHEO3

Notice that the apastron is at 2020 and the periastron is at 2070. Therefore, half of the orbit is covered in 50 years, and the total orbit is 100 years (since the orbit is symmetrical along the line through the foci).

(I'm not entirely certain that those are in fact the periastron and apastron, but I've seen the question before so I'm pretty sure this is correct)
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themightyweeaboo
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### Re: Astronomy C

Unome wrote:
themightyweeaboo wrote:How would you solve for period in this problem?
https://m.imgur.com/a/GHEO3

Notice that the apastron is at 2020 and the periastron is at 2070. Therefore, half of the orbit is covered in 50 years, and the total orbit is 100 years (since the orbit is symmetrical along the line through the foci).

(I'm not entirely certain that those are in fact the periastron and apastron, but I've seen the question before so I'm pretty sure this is correct)

The answer sheet says the period is 87.7 though...

jonboyage
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### Re: Astronomy C

themightyweeaboo wrote:
Unome wrote:
themightyweeaboo wrote:How would you solve for period in this problem?
https://m.imgur.com/a/GHEO3

Notice that the apastron is at 2020 and the periastron is at 2070. Therefore, half of the orbit is covered in 50 years, and the total orbit is 100 years (since the orbit is symmetrical along the line through the foci).

(I'm not entirely certain that those are in fact the periastron and apastron, but I've seen the question before so I'm pretty sure this is correct)

The answer sheet says the period is 87.7 though...

Period is the last thing you’re going to find. You have to go through parts a, b, and c to finally get to the rad/sec and from there get the period.
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themightyweeaboo
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### Re: Astronomy C

jonboyage wrote:
themightyweeaboo wrote:
Unome wrote:Notice that the apastron is at 2020 and the periastron is at 2070. Therefore, half of the orbit is covered in 50 years, and the total orbit is 100 years (since the orbit is symmetrical along the line through the foci).

(I'm not entirely certain that those are in fact the periastron and apastron, but I've seen the question before so I'm pretty sure this is correct)

The answer sheet says the period is 87.7 though...

Period is the last thing you’re going to find. You have to go through parts a, b, and c to finally get to the rad/sec and from there get the period.

Ohhhhhh, that's why...

It's a bit weirdly written, that's why I got confused

themightyweeaboo
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### Re: Astronomy C

Also, does anyone know a formula I could use to solve this?

The ratio of orbital velocities for a star to its planet is 0.0083. The system has an inclination derived of
75 degrees, and the mass of the star is 0.66 solar masses. What is the mass of the planet in Jupiter
masses?

themightyweeaboo
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### Re: Astronomy C

Also, does anyone know a formula I could use to solve this?

The ratio of orbital velocities for a star to its planet is 0.0083. The system has an inclination derived of
75 degrees, and the mass of the star is 0.66 solar masses. What is the mass of the planet in Jupiter
masses?

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### Re: Astronomy C

Completely random, but I'm working on my DSO list and am speculating the HII region in the star formation region NGC 7822. I cropped this image to what I believe to be a (or the) HII region. My actual question is, though, is the bright star in the center of this image BD+66 1673? This cropped image was taken from a ground based image of NGC 7822.
EDIT: If I'm wrong about the HII region, can someone please point it out on the larger scale image of the region? Thanks!
https://image.prntscr.com/image/DR1NfHVxQYOSnEZMMDCcjQ.png
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flickering
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### Re: Astronomy C

Hi,

I'm new to Astronomy because I've just recently been put into this event, and while I was working on my DSOs, I noticed that for many of them, like Geminga, have contradictory information on different sites about stuff such as distance (in light-years) to the DSO. I read through the forum and it says to use research papers (I got 160 lightyears from verified research papers for Geminga), but what if test writers use the value on wikipedia or another site? Wikipedia says 800 lightyears, and other sources say 300 or even 100 lightyears :/

Thank you for any replies!

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### Re: Astronomy C

flickering wrote:Hi,

I'm new to Astronomy because I've just recently been put into this event, and while I was working on my DSOs, I noticed that for many of them, like Geminga, have contradictory information on different sites about stuff such as distance (in light-years) to the DSO. I read through the forum and it says to use research papers (I got 160 lightyears from verified research papers for Geminga), but what if test writers use the value on wikipedia or another site? Wikipedia says 800 lightyears, and other sources say 300 or even 100 lightyears :/

Thank you for any replies!

First, about the questions from themightweeaboo, sorry as usual for the mistakes >.<. I've tried to ask the nats people once or twice to replace it, but I guess they forgot...I'm also really busy writing new tests and trying not to make mistakes again, though more important is finding people to help check questions.

I'll leave the questions before this one to someone else.

For distances, I would say that these values aren't all precisely contradictory. Measurements have errorbars, and sometimes you can only estimate a distance so well with different methods (trig parallax, spectroscopic parallax, etc). Using papers can be good, but it's not good if you don't understand the method they used. One issue with papers is often the methods aren't written for the public, they're written for people who have spent multiple years studying some overly specific area. I mostly read papers for concepts to look up based on the intro. or notable results for a specific object from the abstract / conclusion. This obviously takes practice, and it's not easy by any means. which is why I think it helps if you're new to spend more time studying basics or maybe lecture notes from an intro class.

Maybe what you can do is print the Wikipedia page and then have a separate "quick cheat sheet" page with some notable values from a separate source. Either that or put a range and note the references you use. All that said, I really haven't seen many cases where the "correct" distance (which is hard to tell because few list the method they use to find distances) is THAT essential to know...do test writers really rely on specific numbers that are admittedly questionable?
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genew
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### Re: Astronomy C

Hi! This is my first year in astronomy and I'm struggling a bit to understand all of these new concepts, especially since my physics, chemistry, etc. knowledge is still a bit limited. I have a couple of questions:
I was looking at example questions on scioly forums and I was wondering how you would identify which element is causing the largest emission line here.
Is there a type of element related to a certain wavelength or would it depend on the type of star?

Also, how would you find the angular size of a semi-major axis without knowing the period first?

Sorry if these questions are poorly worded or don't make sense, I'm still really confused about the overall topic of astronomy.