## Astronomy C

astronomybuff
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### Re: Astronomy C

nobodynobody wrote:
September 23rd, 2020, 12:41 pm
a) An elliptical galaxy has been observed to have an Ha line of 715.68 nm, while it's "true" wavelength of Ha lines is 656.28 nm. How far away is the galaxy, in parsecs?
b) How long is the major axis of the galaxy, in parsecs?

A) Using the 2 wavelengths, the redshift is calculated to be 0.090510. Since that is a small redshift, I'll approximate the recessional velocity to be about 2.7153 * 10^4 km/s. Assuming Hubble's constant to be 72, the distance is 377 mpc, or 3.77 * 10^8 parsecs.
B) I'm not sure if you can calculate the major axis of the galaxy using the information from the problem?
a is correct. Hm yeah, I got an answer when doing b before, but now I'm not quite sure how to do it... anyone else have an idea?

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### Re: Astronomy C

astronomybuff wrote:
September 24th, 2020, 9:54 am
nobodynobody wrote:
September 23rd, 2020, 12:41 pm
a) An elliptical galaxy has been observed to have an Ha line of 715.68 nm, while it's "true" wavelength of Ha lines is 656.28 nm. How far away is the galaxy, in parsecs?
b) How long is the major axis of the galaxy, in parsecs?

A) Using the 2 wavelengths, the redshift is calculated to be 0.090510. Since that is a small redshift, I'll approximate the recessional velocity to be about 2.7153 * 10^4 km/s. Assuming Hubble's constant to be 72, the distance is 377 mpc, or 3.77 * 10^8 parsecs.
B) I'm not sure if you can calculate the major axis of the galaxy using the information from the problem?
a is correct. Hm yeah, I got an answer when doing b before, but now I'm not quite sure how to do it... anyone else have an idea?
b. could be straightforward if angular diameter was given, but I can't think of a good way to try to guess the major axis of a galaxy using only distance/redshift.

EDIT: Rewording
Last edited by RiverWalker88 on September 24th, 2020, 10:12 am, edited 1 time in total.
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### Re: Astronomy C

Revive!

Go to js9.si.edu/nso/nso.html and remotely open the image at "ftp://cda.harvard.edu/pub/science/ao01/ ... t2.fits.gz". (Caution: This link will lead to a file that is ~38 megabytes that you probably don't want to download. It's not harmful, it's just kind of big).
`Open the file menu and click on "Open Remote". For this particular image, you will use a proxy server, so leave that bubble filled. Paste the link above into the search bar and click "open". It may take a moment for the image to load.`
1. What is the strongest period of the central object?
2. Do the jets in this image display periodicity? If so, is this possibly a result of the central object?
3. How many photons does the brightest area of the central object emit per second?
4. Are the jets in this image approximately the same (with the exception of their position and direction of outflow)? How can you tell?
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### Re: Astronomy C

RiverWalker88 wrote:
October 5th, 2020, 10:46 pm
Revive!

Go to js9.si.edu/nso/nso.html and remotely open the image at "ftp://cda.harvard.edu/pub/science/ao01/ ... t2.fits.gz". (Caution: This link will lead to a file that is ~38 megabytes that you probably don't want to download. It's not harmful, it's just kind of big).
`Open the file menu and click on "Open Remote". For this particular image, you will use a proxy server, so leave that bubble filled. Paste the link above into the search bar and click "open". It may take a moment for the image to load.`
1. What is the strongest period of the central object?
2. Do the jets in this image display periodicity? If so, is this possibly a result of the central object?
3. How many photons does the brightest area of the central object emit per second?
4. Are the jets in this image approximately the same (with the exception of their position and direction of outflow)? How can you tell?
1. 250 sec
2. Yes & yes (because they have the same period as the central object)
3. Approximately 0.23 photons/sec (0.0397 photons/arcsec2/sec over 5.81 arcsec2). If you meant the brightest pixel, then more like 0.13 photons/sec.
4. They are approximately the same, because they have similar lengths, periods, and light curves. They also both have brighter regions farther out on the jets (seen on the 3d plots). The main differences are that the upper jet stays brighter further out instead of just having a bright spot in the middle (like the lower jet), and the upper jet overall emits more photons.
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### Re: Astronomy C

AstroClarinet wrote:
October 11th, 2020, 6:39 am
RiverWalker88 wrote:
October 5th, 2020, 10:46 pm
Revive!

Go to js9.si.edu/nso/nso.html and remotely open the image at "ftp://cda.harvard.edu/pub/science/ao01/ ... t2.fits.gz". (Caution: This link will lead to a file that is ~38 megabytes that you probably don't want to download. It's not harmful, it's just kind of big).
`Open the file menu and click on "Open Remote". For this particular image, you will use a proxy server, so leave that bubble filled. Paste the link above into the search bar and click "open". It may take a moment for the image to load.`
1. What is the strongest period of the central object?
2. Do the jets in this image display periodicity? If so, is this possibly a result of the central object?
3. How many photons does the brightest area of the central object emit per second?
4. Are the jets in this image approximately the same (with the exception of their position and direction of outflow)? How can you tell?
1. 250 sec
2. Yes & yes (because they have the same period as the central object)
3. Approximately 0.23 photons/sec (0.0397 photons/arcsec2/sec over 5.81 arcsec2). If you meant the brightest pixel, then more like 0.13 photons/sec.
4. They are approximately the same, because they have similar lengths, periods, and light curves. They also both have brighter regions farther out on the jets (seen on the 3d plots). The main differences are that the upper jet stays brighter further out instead of just having a bright spot in the middle (like the lower jet), and the upper jet overall emits more photons.
1. `I got 166.772 seconds for this one. I circled the central region, ran the power spectrum, and got a peak at 0.005998 Hz. When converted to seconds, I got 166.772. However, there was an evident peak (albeit smaller, but evident) around 0.004Hz, so there is some periodicity around 250s as well.`
2. ```I found that the jets displayed only mostly constant emission, and really no periodicity (see note at end) in their power spectrum. However, if the central object was left encircled or was in the region where the jet light curve was measured, it was bright enough that it showed its light curve peaks in the power spectrum of the jet.

I did double check to see, and there is a peak in the light curve of the jets without the central object at around ~0.004Hz, meaning at least weak periodicity at around 250 seconds, which likely was caused by the central object.```
3. `Yep! We got a similar answer (0.23 vs 0.21), with variability likely a result of different circling.`
4. `I would say no on this one, because the energy spectra of the four different jets are all pretty different, meaning that the material in them is different. However, your analysis is really good, and way more in-depth than I went.`
In-depth Explanation
For anyone new to JS9 or unsure how this was done, here's how I came to my answers.
1. `To determine the period of the power spectrum, on would have to first encircle the central object (most likely with a circular region). Then, you would open the analysis menu and run the "Light Curve" function under "NSO Analysis". Close the light curve (It will be noisy and useless) and run the "Power Spectrum" analysis under "NSO Analysis". This will give you a series of peaks. Click and drag the area around the highest peak (you should see a yellowish box surround it) to zoom into that peak to get a better measurement of where it lands. The x value of this peak is the period in Hertz, so you need to convert it so seconds by dividing 1 by the measure in Hertz. This will give you the period in seconds.`
2. `To find the period of the jets, do the same process as above, but place a region (a rectangle, most likely) around individual jets (I did each separately, but getting an idea from 1 or 2 should work) and run the analysis you ran in part a. Compare it to the period you found in part a.`
3. `To complete this one, first encircle the central object (I used the vague term of "Brightest area", just ignore that). Then, run "Flux in Regions" under "NSO Analysis". This will give you an entry that tells you your flux in photons/arcsecond^2/second. To get your answer in photons/second, you can cancel out the arcsecond^2 with the area of the region. To find this, use "Counts in Regions". You can then use the area column to determine the area of the region in arcsec^2.`
4. `As seen above, there are many ways to approach this particular question. I compared the energy spectra of the four different jets (Analysis > Energy Spectrum), but you could also have looked at the lengths, brightness, periods, and overall features of the jets.`
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### Re: Astronomy C

``` 1) I kind of ignored the 2nd pair of jets... I mean I noticed they were there but I guess I assumed they weren't important?
2) I didn't know that the analyses looked at all the regions that were open. I suppose I should have realized that when I started getting duplicate analyses for different regions.
3) I used the period fold instead of the power spectrum, which probably wasn't a great idea because the period fold requires a lot of random guessing. For some reason though, 250 Hz looked stronger in the period fold than 167 Hz.

Seeing how many mistakes I made, this was good practice for me! ```
Here are the new questions:
1. What creates the narrow and broad lines in AGN spectra, and how?
2. PSS 0133+0400 has a redshift of 4.15 and proper motions of 0.437 mas/yr (in the negative RA direction; already corrected) and 0.100 mas/yr (in the positive Dec direction). Estimate its distance in gigalight-years.
3. Find the magnitude of the total/space velocity of PSS 0133+0400, relative to our solar system, in km/s.
Bonus: Calculate the wavelength (in micrometers) of the Pfund limit (Hydrogen line from n=5 to n=infinity).
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