41 replies to this topic

[Tulloch]

Yeah, probably the wrong forum, you'd need the dedicated double star splitters for this one...

[bunyon]

Yes. It might even be worth a moderator moving this to the double star forum. I know it doesn’t seem to fit but that’s functionally what this task is.

This also isn’t “lucky imaging”. We diverted into triton. I record Triton at ~200 ms exposure. Charon is 100 times dimmer so the necessary exposure will be multiple seconds. At that point you need near perfect seeing and guiding at ~5,000 mm EFL.

[RedLionNJ]

Yes. It might even be worth a moderator moving this to the double star forum. I know it doesn’t seem to fit but that’s functionally what this task is.

This also isn’t “lucky imaging”. We diverted into triton. I record Triton at ~200 ms exposure. Charon is 100 times dimmer so the necessary exposure will be multiple seconds. At that point you need near perfect seeing and guiding at ~5,000 mm EFL.

This wouldn't last two minutes in the double star forum. It would get bounced back here almost immediately.

 

I do agree the techniques/challenge are more along the lines of attempting to capture (at least as a non-circular pattern) a close double. But if it was easy to do (or even relatively hard to do, but still do-able), someone would have done it years ago. The technology available to amateurs hasn't really changed much lately.

[RedLionNJ]

Professionals Rik Hill & Seth Hansell claimed to have visually cleanly split Pluto & Charon with the Catalina 2-meter in 1996. From Rik's description, seeing was phenomenal - worthy of 60+ inches of aperture.  It would stand to reason somebody may have a chance to image the pair with the Mt Wilson 60-inch at some point.

[Redbetter]

Yes. It might even be worth a moderator moving this to the double star forum. I know it doesn’t seem to fit but that’s functionally what this task is.

This also isn’t “lucky imaging”. We diverted into triton. I record Triton at ~200 ms exposure. Charon is 100 times dimmer so the necessary exposure will be multiple seconds. At that point you need near perfect seeing and guiding at ~5,000 mm EFL.

Triton is not 100 times brighter though.  It is ~ 3 magnitudes brighter, which is roughly 16x.  Plus Charon isn't stuck in the glare of a planet ~5.6 magnitude (~174x) brighter than it is.  (I don't know if that glare impacted the exposure you needed or not.)

 

The question comes down to how long of an exposure does one need to get a few counts around the central intensity of an ~16.5 mag stellar appearing object with a given exposure and aperture.  It doesn't have to be pretty, as long as the scale is sufficient to get enough counts to rise above noise level so that sufficient lucky frames can be stacked for the centroids to be clear for the two bodies.  With larger scopes the time shrinks.  

 

I would be very surprised if a camera cannot capture enough photons in a 1/10 or a few tenths of a second to show a 17 mag star in a 20" scope.  My eye has perhaps 10 times less quantum efficiency than modern sensors, and the eye has about a tenth of a second integration time, yet that is enough to readily pick up 17 mag stars on nights of mediocre seeing.  On a night of very good seeing I can reach 18 with the 20".  

 

What the eye lacks is the ability to do orders of magnitude longer integration times of the best moments while discarding the rest.  That and the eye is not great at splitting tight, uneven pairs near threshold.  (On the other hand, with the 20" in 3/10 seeing I was able to still see the elongation of the extremely tight ~ equal pair Zeta Bootes at 0.18" separation--with what turned out to be the correct PA, and other stars of similar magnitude not presenting an elongated spurious disk.  Repeated the observation with my son a few nights later as confirmation.  But Zeta Boo is bright.)

 

Since people split Pluto-Charon in 1996 visually with a 2 meter without any preparation to do so, that indicates prepared observers could do it with considerably less aperture in excellent seeing.  From looking at a few weeks of orbits it looks like the pair are typically 0.7 to 0.8" apart at present.  

[Tulloch]

This wouldn't last two minutes in the double star forum. It would get bounced back here almost immediately.

 

I do agree the techniques/challenge are more along the lines of attempting to capture (at least as a non-circular pattern) a close double. But if it was easy to do (or even relatively hard to do, but still do-able), someone would have done it years ago. The technology available to amateurs hasn't really changed much lately.

Well, in that case it may never be done. Planetary imagers don't have the skills or experience to do it, and the double star splitters either won't know about it or won't care.

 

Maybe a request posting can sent as a "challenge" to the splitters on their forum, with the results posted here? That way, everyone is happy?

Edited by Tulloch, 27 August 2023 - 05:07 PM.

[bunyon]

I have no doubt a 60 incher with modern tools could do it under good conditions. The biggest issue is that big amateur scopes don’t track accurately or smoothly enough.

Triton isn’t lost in neptunes glare on a chip, it’s well away from it.

[Ittaku]

This also isn’t “lucky imaging”. We diverted into triton. I record Triton at ~200 ms exposure.

For what it's worth, I still manage to capture Triton at 30fps.

[Redbetter]

For what it's worth, I still manage to capture Triton at 30fps.

That's what I was thinking.  

 

I'm assuming that the choice of camera might be a bit different for things like this (double star equivalent) where color of extended objects is not the goal.  Instead the choice would be more about efficiency while minimizing noise.  

[Bob Campbell]

In 2008, a group in Italy apparently did the split with a C14 and the best ccd camera of the time. Much has improved in both equipment and processing algorithms, so surprisingly might be currently doable (for those with the planetary 'big iron')

 

https://www.universe...ur-astronomers/

 

"Medugno used an 14″ Schmidt-Cassegrain telescope, a Starlight Xpress SXV-H9 CCD camera and a R-IR passband filter.

The image was processed using the Lucy-Richardson Algorithm of the RAW image, composed of 21 frames of 6 seconds of exposure each, with a focal of 8900mm. “All data confirm the image: the magnitude, separation, and position angle,” said Gasparri."

 

 

 

Bob

Edited by Bob Campbell, 27 August 2023 - 09:03 PM.

[555aaa]

Well it so happens that right now  Pluto is a couple arc minutes from the double star WDS B 464 which is 10th magnitude and has 0.5" separation. So an additive stack on that star with discarding the bad images should show elongated images for both.

[Redbetter]

In 2008, a group in Italy apparently did the split with a C14 and the best ccd camera of the time. Much has improved in both equipment and processing algorithms, so surprisingly might be currently doable (for those with the planetary 'big iron')

 

https://www.universe...ur-astronomers/

 

"Medugno used an 14″ Schmidt-Cassegrain telescope, a Starlight Xpress SXV-H9 CCD camera and a R-IR passband filter.

The image was processed using the Lucy-Richardson Algorithm of the RAW image, composed of 21 frames of 6 seconds of exposure each, with a focal of 8900mm. “All data confirm the image: the magnitude, separation, and position angle,” said Gasparri."

 

charon-reduced.jpg

 

 

Bob

Interesting.  Wouldn't that passband be of lower resolution (for the instrumental aperture, not for the pixel size) than something peaking in the 500nm range?   I would think it beneficial to get a stronger signal and reduce the exposure time at the same scale.  With 20" of aperture the brightness is twice as great at the same scale.  But I am not an imager.

 

What would be the camera of choice for this task today if one was setting something up for dim double star resolution?   (Assuming one was attempting to measure position angle and separation of the centroids.)  I am wondering how many frames one might be able to get and what their exposure times would be.

[Bob Campbell]

Interesting.  Wouldn't that passband be of lower resolution (for the instrumental aperture, not for the pixel size) than something peaking in the 500nm range?   I would think it beneficial to get a stronger signal and reduce the exposure time at the same scale.  With 20" of aperture the brightness is twice as great at the same scale.  But I am not an imager.

 

What would be the camera of choice for this task today if one was setting something up for dim double star resolution?   (Assuming one was attempting to measure position angle and separation of the centroids.)  I am wondering how many frames one might be able to get and what their exposure times would be.

that camera had > 6 micron pixels. Modern cmos planetary cameras have 2 micron pixels (asi678mc for example)

 

2 micron pixels at 8900 mm yields a resolution of 0.05 arc secs, so there would be .7/.05=14  pixels in the gap between pluto and charon as furthest separation. The C14 has an intrinsic resolution (rayleigh) of 0.39 arcsec, so it would not be taking advantage of the full 0.05 arcsec.  It would take nearly a 100" scope to be able to get rayleigh down to 0.05 arcsec.

 

Exposures of a few seconds, stacked maybe 100 might do the trick. I would stick to a simple uv/ir cut filter as a first shot. I agree I do not understand the red-ir pass filter they used.

 

The real key is atmospheric seeing. Excellent is usually considered 0.2-0.5 arcsecs. So even with modern cmos cameras, the best one could hope for with a c14 would likely be a dawes type separation: still connected but elongated as in that graphic above. 

 

Bob

[Redbetter]

I am thinking that an intermediate pixel size and/or shorter focal length than they employed might do best, because it would provide the needed resolution, but also allow shorter exposures at the resolution of the aperture (fewer pixels per spurious disk area).  That would allow more lucky samples for a stack and better opportunity to capture the best moments (shorter increments because seeing has a speed/frequency.)

 

One thing I see visually is that the shorter/bluer wavelengths suffer the most from the seeing, and blue in particular introduces more scatter glare visually, but I don't know how much of this is my eye and how much is the image from the scope's focal plane.  This is why in all but the best seeing I employ a #25 red for Mars--of course Mars has brightness to spare and much of its contrast improves with red.  

 

For this case with Pluto still being somewhat low, an ADC might be needed in combination with a filter cutting out the violet and IR ends.  That would tighten things up vertically but probably not cost that much in terms of photon count.

[azure1961p]

I was thinking with all the incredible imaging and large apertures amateurs use today at least an elongation was possible.  I'll bet one day in the distant future when imagers can record 14-15v almost instantly to stack, that day will come, and probably for a C14.

 

Thanks all.

 

Pete

[RedLionNJ]

I was thinking with all the incredible imaging and large apertures amateurs use today at least an elongation was possible.  I'll bet one day in the distant future when imagers can record 14-15v almost instantly to stack, that day will come, and probably for a C14.

 

Thanks all.

 

Pete

I believe, with very good seeing and at least a 12-inch scope located in the southern hemisphere (and a lot of experience/skill), an elongation (to be compared with a different angle of elongation under similar circumstances one or more nights later) should indeed be possible to capture.  Normal "lucky imaging" techniques should suffice, but my primary concern is how long individual exposures would have to be, vs any undulations due to seeing.

 

Lucky imaging for the likes of Jupiter and Mars is executed with frame durations in the order of single digit milliseconds.  That would not be enough to record the 14th/16th magnitude pair, even as an apparently single object.

 

 

Angular separation between the objects isn't so much of an issue. I checked a minute or so ago (no special time) and they were about 0.74 arcsec apart. But blurring the two objects into one should be perfectly acceptable as long as there's a visible elongation.

 

So, with Pluto at about RA 20h and Dec -22 - any of the regular southern hemisphere imagers on here up for it this year?

[Xilman]

Like JMP mentioned, practice on Neptune and Triton first, then try and get as many moons of Uranus as possible, then on to your goal. You may need some years to practice and a "small" scope upgrade in the meantime.   For comparison, this is Neptune and Triton last year with field stars and their magnitudes through a 12" Newtonian and ZWO 183mm camera. Which is no comparison at all because Pluto and Charon will be 1000X harder. Good luck. You're gonna need it.

 

Neptune_2022_1112_Triton3.jpg

Only just found this thread, so apologies for such a late response.

 

I have images of Sycorax and Caliban (U-XVI and U-XVII) as well as Triton and  Nereid (N-I and N-II).  Not yet tried very hard for Ariel, Umbriel, Titania, Oberon and Miranda (U-I through U-V).

 

Images at links within http://www.astropalm...satellites.html

 

Paul