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Is research on the cometary ion tails possible?

Comet Imaging Observing Astrophotography
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#1 CelestialSail

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Posted 10 February 2024 - 11:33 AM

Greetings, everyone.

I’ve been an astro-geek for years, and I’ve always had a sweet spot for comets, specially since I witnessed comet NEOWISE from one of the darkest night skies in the world in 2020.

Lately I’ve been pretty interested in doing research of the gas/ion tail that comets often form. Their insanely complex structure and behavior has always amazed me. However, I wanted to focus a bit more on their composition. I was thinking if it would be possible that these tails could have their own internal structure: for example, depending on the different molecules that form it, what if we could detect certain structures and associate them with a certain molecule’s behavior with solar wind?

Or even more remarkable: what if I could discover another kind of tail which is mainly composed of a certain gas, like ammonia? As unlikely as this is, people have already made this once with the elusive orange sodium tail, found on some comets that make drastic approaches to our star.

I commented this to a close yet distant friend of mine (I’m from Spain, he is from the Netherlands), and he would like to collaborate, but as two teenagers who still have a lot to learn about these rebellious ice rocks, we may need a bit of research and help.

I’d love to hear some tips on where to look for answers and how to look for them, and if someone wishes to collaborate in this recently started idea, I’d love to have someone’s help, specially if they own fast rigs and stuff lol. My rig is pretty good too, but I think I lack a bit of experience in comet astrophotography (As you can see on my attempt on comet Nishimura from 2023, cropped bcs of file size.) , so I’m willing to hear your replies and share knowledge.Besides, I think that most of us know how far can the amateur astronomic community can go if we join forces.

 

IMG_0748.jpeg

I’ll be waiting for any answer. Thank you for your time!

—CelestialSail


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#2 CelestialSail

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Posted 10 February 2024 - 12:31 PM

My plan would be for everyone who wishes to collaborate to photograph bright comets, like the upcoming 12P or C/2023 A3, and use narrowband filters which wavelengths correspond to certain molecules within a comet's composition, like C2, ammonia or methane.

If anyone has any knowledge about these lightwaves, do share. It will be a big help to isolate the components of the gas tail and we may see some new details kn its behavior.

#3 Tapio

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Posted 10 February 2024 - 12:48 PM

I've had CN cyan filter over 2 years now but still waiting for bright enough comet for it.
Too bad 12P is going to southern hemisphere when it's brightest.
Now I'm waiting to get sodium filter (for Mercury tail).
People do have methane filters for Jupiter but others are rare I think.

Have you done research on comet chemistry?
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#4 CelestialSail

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Posted 10 February 2024 - 12:56 PM

I've had CN cyan filter over 2 years now but still waiting for bright enough comet for it.
Too bad 12P is going to southern hemisphere when it's brightest.
Now I'm waiting to get sodium filter (for Mercury tail).
People do have methane filters for Jupiter but others are rare I think.

Have you done research on comet chemistry?

12P will be pretty decent at mid-northern latitudes tbh, so I think I can give it a shot.

 

Tbh I don’t have pretty much interest on sodium bcs it lacks detail and has already been discovered in 4 comets. I’ve done little research but I do want to extend my knowledge on it. My main issue is that I can’t find accurate articles with the propper wavelengths of the elements. I did see an article which said that ammonia shines in the exact same wavelength that the 540nm solar continuum (I have the filter, so that’s cool), but idk if it’s true since ionised ammonia is in the 510nm wavelength in other places. I also saw that methanol is pretty common in comets, so any wavelength would be good to know.
 

And about methane, would the methane filter for jupiter work? Or is anything else needed?


Edited by CelestialSail, 10 February 2024 - 01:01 PM.


#5 Octans

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Posted 10 February 2024 - 03:22 PM

Neutral molecules don't significantly react with the solar wind, so you won't see much in the way of structure in any of those (aside from possibly jets in the coma, which you'd also see for just dust). Ions do, but they are carried away by the solar wind extremely quickly, so you need a whole lot of ions to make a visible ion tail. Usually, the only ones accessible with even fairly large telescopes are CO+, H2O+, and sometimes N2+ depending on the comet.

 

Also, very few molecules have noticeable emission at optical wavelengths. All the emission you see is essentially from a few select pieces of (invisible) bigger molecules that broke down in sunlight. Ammonia (NH3), for example, has no optical emission (at least in the cometary environment), but a fragment of ammonia NH2 does. An NH2 image, however, just shows a nearly featureless blob, and the only reason people use that filter is to measure how much of it a comet has compared to other gases.

Here's a catalog of some optical comet lines: https://web.gps.calt...et/echelle.html


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#6 CelestialSail

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Posted 10 February 2024 - 03:37 PM

Neutral molecules don't significantly react with the solar wind, so you won't see much in the way of structure in any of those (aside from possibly jets in the coma, which you'd also see for just dust). Ions do, but they are carried away by the solar wind extremely quickly, so you need a whole lot of ions to make a visible ion tail. Usually, the only ones accessible with even fairly large telescopes are CO+, H2O+, and sometimes N2+ depending on the comet.

 

Also, very few molecules have noticeable emission at optical wavelengths. All the emission you see is essentially from a few select pieces of (invisible) bigger molecules that broke down in sunlight. Ammonia (NH3), for example, has no optical emission (at least in the cometary environment), but a fragment of ammonia NH2 does. An NH2 image, however, just shows a nearly featureless blob, and the only reason people use that filter is to measure how much of it a comet has compared to other gases.

Here's a catalog of some optical comet lines: https://web.gps.calt...et/echelle.html

Thanks so much for the data! I’m guessing the numbers in the archives are in Armstrongs, right?

 

I was hoping to see any distinct structure in the ion tail and try to associate it to a specific element, kind of like discovering a new part of the tail, like the Sodium tail that has been elusively observed of comets that approached the sun.

 

My main focus in this is to understand the ion tail’s behavior better by analising its structure, or even making new discoveries, so… Is there any potential element or molecule that could behave in a similar way to that of the Sodium? Maybe we can instead distinguish regions within the ion tail that are more vulnerable to solar wind than others?


Edited by CelestialSail, 10 February 2024 - 03:46 PM.


#7 Octans

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Posted 10 February 2024 - 03:54 PM

Those wavelengths are in angstroms = 0.1 nm.

Sodium is actually very commonly seen, visible pretty much on nearly every half decently bright long period comet that gets to <0.5 au from the Sun, first seen all the way back in 1882 on Comet Wells (now called C/1882 F1). In theory, all the other alkali metals (group 1 on the periodic table, minus hydrogen) should have very similar tails, but are dimmer because there's less of them in the comet, and they get destroyed by UV radiation more quickly. Potassium is the only other one that's been actually seen, but it's usually only ~1/50th the brightness of sodium (with a shorter tail, so that brightness is more concentrated in the head), and at 766/770 nm.

 

For emission by comets near the Sun, here's a bunch seen in Ikeya-Seki, which was the brightest comet observed since 1882: https://adsabs.harva...AJ.....74..929S


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#8 CelestialSail

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Posted 10 February 2024 - 04:02 PM

Those wavelengths are in angstroms = 0.1 nm.

Sodium is actually very commonly seen, visible pretty much on nearly every half decently bright long period comet that gets to <0.5 au from the Sun, first seen all the way back in 1882 on Comet Wells (now called C/1882 F1). In theory, all the other alkali metals (group 1 on the periodic table, minus hydrogen) should have very similar tails, but are dimmer because there's less of them in the comet, and they get destroyed by UV radiation more quickly. Potassium is the only other one that's been actually seen, but it's usually only ~1/50th the brightness of sodium (with a shorter tail, so that brightness is more concentrated in the head), and at 766/770 nm.

 

For emission by comets near the Sun, here's a bunch seen in Ikeya-Seki, which was the brightest comet observed since 1882: https://adsabs.harva...AJ.....74..929S

Again, thank you so much for the data! Seems like the potassium tail could be attempted… I’m also curious about iron and vanadium. I do know that an Iron tail was flawlessly imaged with the STEREO Observatory on comet C/2006 P1 (McNaught), but I’ve never heard about Vanadium. I’m guessing it’s extremely faint anyway. Besides, the light emmited by iron seems pretty broad too. I also see several elements near the 400mm boundary, but those will probably be the hardest to capture. I will definitely look into potasium though! Thanks so much once again. I still hope I can find some other stuff to investigate. Where could I get a 770nm filter? (1.25” or 2” if possible)


Edited by CelestialSail, 10 February 2024 - 06:19 PM.


#9 robin_astro

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Posted 10 February 2024 - 07:02 PM

Spectroscopy of the coma is straightforward for amateurs but some measurements can be made into the tail using spectroscopy and modest amateur instruments but only on the brightest comets

https://britastro.or...e77e0992eb70386

https://britastro.or...8b30a0a785a7ab3

 

Robin


Edited by robin_astro, 10 February 2024 - 07:06 PM.


#10 Octans

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Posted 10 February 2024 - 07:11 PM

Again, thank you so much for the data! Seems like the potassium tail could be attempted… I’m also curious about iron and vanadium. I do know that an Iron tail was flawlessly imaged with the STEREO Observatory on comet C/2006 P1 (McNaught), but I’ve never heard about Vanadium. I’m guessing it’s extremely faint anyway. Besides, the light emmited by iron seems pretty broad too. I also see several elements near the 400mm boundary, but those will probably be the hardest to capture. I will definitely look into potasium though! Thanks so much once again. I still hope I can find some other stuff to investigate. Where could I get a 770nm filter? (1.25” or 2” if possible)

Here's a 50.4 mm diameter 769.9 nm filter with 1 nm bandpass that should transmit potassium: https://alluxa.com/o...arrow-bandpass/ Narrowband filters like these are not mass produced in the way H-alpha or other common amateur astronomy filters are, so note that they will all be quite expensive.



#11 robin_astro

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Posted 10 February 2024 - 07:12 PM

There is a video of a talk I gave on the spectroscopic analysis of comets by amateurs at a BAA meeting here

https://britastro.or...obin-leadbeater



#12 CelestialSail

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Posted 11 February 2024 - 01:38 AM

There is a video of a talk I gave on the spectroscopic analysis of comets by amateurs at a BAA meeting here

https://britastro.or...obin-leadbeater

Thanks a lot for the graphics for NEOWISE and the video! It shows some interesting components that could be isolated.



#13 CelestialSail

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Posted 11 February 2024 - 01:39 AM

Here's a 50.4 mm diameter 769.9 nm filter with 1 nm bandpass that should transmit potassium: https://alluxa.com/o...arrow-bandpass/ Narrowband filters like these are not mass produced in the way H-alpha or other common amateur astronomy filters are, so note that they will all be quite expensive.

Thanks for the filter, but jesus that IS expensive, even more than a small observatory mount… I did find one at a 20nm bandwidth for like 60 bucks, but it still needs an 1 1/4 mount to be threaded into a telescope. Would 20nm of bandwidth be enough?


Edited by CelestialSail, 11 February 2024 - 01:45 AM.


#14 Octans

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Posted 11 February 2024 - 03:27 AM

20 nm is probably a bit too wide for most comets. Using the rough relation that sodium is ~50x brighter, this will be roughly equivalent to trying to observe the sodium tail with a bandpass ~50 x 20 nm ~ 1000 nm wide, which is comparable/a bit worse than imaging a sodium tail with a monochrome camera unfiltered. Certainly not impossible, but that should give you a sense of the difficulty, if you've had some experience imaging sodium before.


Edited by Octans, 11 February 2024 - 03:28 AM.


#15 CelestialSail

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Posted 11 February 2024 - 03:40 AM

20 nm is probably a bit too wide for most comets. Using the rough relation that sodium is ~50x brighter, this will be roughly equivalent to trying to observe the sodium tail with a bandpass ~50 x 20 nm ~ 1000 nm wide, which is comparable/a bit worse than imaging a sodium tail with a monochrome camera unfiltered. Certainly not impossible, but that should give you a sense of the difficulty, if you've had some experience imaging sodium before.

I see… I haven’t really tried to directly image sodium with a filter ever, but I guess that a relation like that is better than just going broadband… More narrow channels are pretty much impossible to obtain and definitely not worth the money for a single experiment (that may not happen anyway if C/2023 A3 misbehaves).

 

Nonetheless, I did fine a small article that implied that the Na/K ratio was around 15 (supposedly due to strong photoionization) when getting closer to the pseudo-nucleus and coma of comet C/2011 L4, so, as you’ve mentioned, photographing the coma and the very beginning of the tail might be my best chance at imaging a K tail, possibly for the first time ever (I’ve only seen spectrum detections so far, not actual images.).

 

I do wonder, though, I have a OSC camera (which makes this even harder lol, might have to do a 2x2bin to mono to get decent signal). What hue would the potassium tail have? (I was thinking of purple, since my OSC camera detects mear infrarreds in red and later on in blue, but it’s probably a dark red.)


Edited by CelestialSail, 11 February 2024 - 07:43 AM.


#16 Octans

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Posted 11 February 2024 - 07:10 AM

With a wide filter, you'll have the most trouble with the beginning of the tail because there, it's buried in with the dust. An extremely narrow filter is needed to improve the contrast between the emission and dust. Without a narrow filter, you don't even usually see a comet's sodium tail except the very outermost portion where it's separated from the dust tail. C/2023 A3 will be a quite a bad target for this sort of thing regardless of how bright it ends up, as it firstly gets only modestly close to the Sun (0.39 au is more than 2x the distance of C/2006 P1), and most of its brightness near peak will come from forward scattering of its dust, which will likely completely drown out all gas emission anywhere the dust tail reaches, even with extremely narrow filters.

Color will depend on the transmission of the individual Bayer matrix filters of your camera, but with most of the Sony detectors, 770 nm transmits through red and green more than blue, so will probably look yellow or orange similar to sodium.

 

For a more accessible challenge, have a try at Mercury's sodium tail, which does not compete with any dust. With decent transparency, you should be able to get it with the red/green channels of your OSC camera with no filter at all.


Edited by Octans, 11 February 2024 - 07:13 AM.

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#17 CelestialSail

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Posted 11 February 2024 - 07:39 AM

With a wide filter, you'll have the most trouble with the beginning of the tail because there, it's buried in with the dust. An extremely narrow filter is needed to improve the contrast between the emission and dust. Without a narrow filter, you don't even usually see a comet's sodium tail except the very outermost portion where it's separated from the dust tail. C/2023 A3 will be a quite a bad target for this sort of thing regardless of how bright it ends up, as it firstly gets only modestly close to the Sun (0.39 au is more than 2x the distance of C/2006 P1), and most of its brightness near peak will come from forward scattering of its dust, which will likely completely drown out all gas emission anywhere the dust tail reaches, even with extremely narrow filters.

Color will depend on the transmission of the individual Bayer matrix filters of your camera, but with most of the Sony detectors, 770 nm transmits through red and green more than blue, so will probably look yellow or orange similar to sodium.

 

For a more accessible challenge, have a try at Mercury's sodium tail, which does not compete with any dust. With decent transparency, you should be able to get it with the red/green channels of your OSC camera with no filter at all.

Already got Mercury's tail as a pale, white streak of light sucessfully 2 years ago, actually. I'm aware of the challenges my plans have, but I don't like seeing this as a challenge, but an attempt to understand cometary behavior better by gathering data... I was also hoping to get people to join on the adquisition of that data, so it is more factible.I'll still wait and see if the comet is actually rich in the materials I'm hoping for (since several comets have exhibited sodium tails at greater distances than 0.4AU) and take action. If not, we can always wait for the best case scenario to repeat.

​ 

I would definitely get the 1nm filter but the price is ridiculous. It’s like selling a 1 euro coin for 400 euros… Definitely can’t afford, and the price is not rlly worth it. I have to get through with whatever I find, unfortunately. More people who would want to participate would help a lot more with this, but I doubt this will get much views…


Edited by CelestialSail, 11 February 2024 - 08:20 AM.


#18 Octans

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Posted 11 February 2024 - 08:55 AM

In terms of science value, an image of a potassium tail is not worth much more than a spectrum (of which, several comets now have potassium spectra), which can already tell you about its relative abundance and also some velocity information. Like sodium, neutral potassium doesn't interact with the solar wind, so it'll also just be a smooth tail, just shorter because of potassium's shorter lifetime. That's not to say to say it wouldn't be scientifically useful at all, just that there are usually easier/cheaper options to get the same information. That applies for basically any filter for uncommonly imaged comet lines. While not always true, there are enough astronomers, professional and amateur, that if something is easy to do with technology more than a few years old, costs less than a few thousand dollars, and is scientifically useful, it has probably already been done. But that doesn't mean doing it again would not be useful.

 

In lieu of spending a huge amount of time and money on custom-designed instruments to tackle very narrow problems, the major scientific value amateur astronomers bring is being able to (collectively) dedicate a whole lot more time to fill in the gaps between the relatively few and far between observations made by large/professional telescopes (on which time is in high demand). There is, in fact, a whole of science left to be done that simply requires either a lot more observations of individual comets filling in the time gaps between professional observations, or observations of different comets without any equivalent professional observations.

 

If you want to get into chemical compositions of comets, you should look into spectroscopy, which is a much cheaper option than buying a filter for every line of interest.

 

If you want to look into solar wind interaction, you should look into CO+ and H2O+ filters, or if you have a dark site and don't want to get new filters, you can just use the blue & red channels of your OSC images and ignore anything smooth (that is either dust or sodium). All ions should interact with the solar wind quite similarly, as there's no chemical reactions involved; they're all just charged particles spiraling down magnetic fields. The only difference in tail appearance you'll see is the H2O+ tail tends to be a bit narrower because H2O ionizes into H2O+ a bit faster than CO ionizes into CO+, but that's a fairly well understood process. See this site for a bunch of ionization rates: https://phidrates.space.swri.edu/

 

If you want to see jets coming out of the nucleus, say, to measure rotation, go for a CN filter (for bright comets, you sometimes don't need any filter at all, as dust & C2 can show jets as well, but CN does so more reliably).

 

There's also value in just producing precise light curves, which can also give information on rotation and activity.


Edited by Octans, 11 February 2024 - 09:08 AM.


#19 CelestialSail

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Posted 11 February 2024 - 09:04 AM

In terms of science value, an image of a potassium tail is not worth much more than a spectrum (of which, several comets now have potassium spectra), which can already tell you about its relative abundance and also some velocity information. Like sodium, neutral potassium doesn't interact with the solar wind, so it'll also just be a smooth tail, just shorter because of potassium's shorter lifetime. That's not to say to say it wouldn't be scientifically useful at all, just that there are usually easier/cheaper options to get the same information. That applies for basically any filter for uncommonly imaged comet lines. While not always true, there are enough astronomers, professional and amateur, that if something is easy to do with technology newer than a few years old, costs less than a few thousand dollars, and is scientifically useful, it has probably already been done. But that doesn't mean doing it again would not be useful.

 

In lieu of spending a huge amount of time and money on custom-designed instruments to tackle very narrow problems, the major scientific value amateur astronomers bring is being able to (collectively) dedicate a whole lot more time to fill in the gaps between the relatively few and far between observations made by large/professional telescopes (on which time is in high demand). There is, in fact, a whole of science left to be done that simply requires either a lot more observations of individual comets filling in the time gaps between professional observations, or observations of different comets without any equivalent professional observations.

 

If you want to get into chemical compositions of comets, you should look into spectroscopy, which is a much cheaper option than buying a filter for every line of interest.

 

If you want to look into solar wind interaction, you should look into CO+ and H2O+ filters, or if you have a dark site and don't want to get new filters, you can just use the blue & red channels of your OSC images and ignore anything smooth (that is either dust or sodium). All ions should interact with the solar wind quite similarly, as there's no chemical reactions involved; they're all just charged particles spiraling down magnetic fields. The only difference in tail appearance you'll see is the H2O+ tail tends to be a bit narrower because H2O ionizes into H2O+ a bit faster than CO ionizes into CO+, but that's a fairly well understood process. See this site for a bunch of ionization rates: https://phidrates.space.swri.edu/

 

If you want to see jets coming out of the nucleus, say, to measure rotation, go for a CN filter (for bright comets, you sometimes don't need any filter at all, as dust & C2 can show jets as well, but CN does so more reliably).

 

There's also value in just producing precise light curves, which can also give information on rotation and activity.

I see… if there is so little value for the image then yeah spectroscopy could be the better choice here. Nonetheless, I’ll still check the H20+ and CO+ filters out (If I can find them).




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