Nereid, mag 18.72 moon of Neptune from Brisbane, 27 Sept 2008
Hello,
After considerable time wrestling with calculations, coordinates and settings, I was delighted to have recorded the trail of Nereid over a period of approx 100 minutes. Nereid was the outermost known moon of Neptune from its discovery in 1949 (by G. Kuiper) until 2002. The parent planet Neptune was positioned just outside the frame at lower left, to avoid saturation blooming of this (bright) magnitude 7.9 body.
Nereid was too far away from Voyager 2 to be properly imaged when the spacecraft visited the Neptune system in 1989. Photos sent back show only its highly irregular shape, and no surface features could be seen at the resolution available. Using the NASA (JPL) Horizons system, I generated an ephemeris for the 27th to 28th Sept at 1 hour intervals and then slewed the ‘scope to the coordinates generated by Horizons. The mean radius of Nereid is 170km and Horizons gave a magnitude of 18.72 for this small body.
Capture details:
Captured using CCDSoft.
Five (5) sub frames of 20 minutes exposure each.
Auto guided using ST7 dual chip (TC211).
FOV 16x11 arc mins. Image scale 1.39 arcsec/pixel.
Processing details:
Dark and Flat reduction in MIRA AP.
Align and Stack in MIRA AP.
Final presentation in CS3.
Wow!! Very impressive cpature. I don't know why but I love these sort of oddball objects. Is Triton lost in the glow of Neptune itself in that picture?
I’ve just completed the animation; it’s not perfect as I just couldn’t seem to normalise the background between frames so there is a little “flashing” between frames.
I’ve also included a mosaic showing the position of Neptune. The Neptune component (lower slot) was a 3 min exposure and you can see the huge bloom. In the (upper) 20 minute frame, at the bottom edge, you can just see a glow which indicated the position of Neptune, well below the border.
I noted that the text book magnitude of Nereid was around 19.6 mag., but decided to have a go as the NASA/JPL Horizons ephemeris indicated 18.72, just within reach of the C9.25.
I just looked at the animation Dennis, what an absolute cracker.
I don't think Mag 18.7 is at your mag limit for this exp time looking at that.
Have you tried .Gif-ing negative images? I find they show much fainter images.
I tried for Sycorax (Mag20.7) of Uranus last night but focus and faint haze beat me.
Did get 3 asteroids in the frame 'though.
Have you done NEA's?
Thanks for those nice words of encouragement – it was a fun project and I was really surprised and pleased with the results. It was one of those sessions where everything just worked so well on the night, truly a night to be savoured!
I just looked at the animation Dennis, what an absolute cracker.
I don't think Mag 18.7 is at your mag limit for this exp time looking at that.
Have you tried .Gif-ing negative images? I find they show much fainter images.
I tried for Sycorax (Mag20.7) of Uranus last night but focus and faint haze beat me.
Did get 3 asteroids in the frame 'though.
Have you done NEA's?
Well done and keep at it.
Hi Jeff
Thanks!
I did have a look at the other fainter moons of Uranus and Neptune and they were all fainter than mag 20, which probably puts them out of reach from my suburban skies some 7km from the Brisbane CBD. It’s a shame that the conditions let you down on your hunt for Sycorax, the 12” F5 should certainly pick it up.
My two favourite (technical) astro programs, The Sky Pro 6 and SkyTools 2 don’t show these fainter moons so I’ve been visiting the NASA JPL Horizons website to obtain the RA and DEC coordinates. I wasted a couple of hours before I realized that the Horizon coordinates were J2000 whereas I was slewing using the Current coordinates. With such a relatively small chip I initially missed Nereid by that much!
I particularly like The Sky Pro 6 because I can use the USNO 2A star catalogues (over ˝ billion stars) down to mag 19+. Do you know of any other catalogues that can take you down to say, mag 20? I’d like to see how deep my 20 minute suburban exposures went.
I’ll try the “negative” approach with the gif and let you know how I get on. I’ve managed to capture a few of the brighter NEA's when they have been suitably positioned and they show some amazing orbital trails in a relatively short period.
In trying to establish the faintest magnitude stars on my Nereid 20 min sub frames, I located a USNO website where you can enter the RA and DEC coordinates and obtain a chart of stars down to around 21 mag.
Having done this, I think that I may have candidate stars of fainter than 20 mag on my Nereid image. These are identified by the letters A & B in the attached files.
I write candidate as you can also see some speckles elsewhere in the cropped frame that are just noise and not “real” objects. Who knows?
Hi Dennis,
I'd say you can easily reach fainter than Nereid going on your last post.
Negative images, for some reson do show fainter stars.
Another method is to take enough images of the field to show a faint minor body and stack them with an offset of the position angle (direction and amount of travel).
Thanks Jeff – this stuff can become quite addictive; both the collection of data then the subsequent scouring of on line resources to better identify the capabilities and performance of one’s gear.
But, I’d rather keep it a hobby than do it as a job! LOL!
Thanks Jeff – this stuff can become quite addictive; both the collection of data then the subsequent scouring of on line resources to better identify the capabilities and performance of one’s gear.
But, I’d rather keep it a hobby than do it as a job! LOL!
Cheers
Dennis
Oh I could do this for a job if the pay was better.
Well, after a bit of research and a few late nights, since the original capture of Nereid I have managed to establish the magnitudes of some of the fainter stars in the stacked 5 x 20 min frame, thanks to the United States Naval Observatory, Flagstaff Station.
Here is a negative image showing stars down to 20 mag. The USNO charts had some of the POSS I and POSS II data for Red (R) Plates and Blue (B) Plates and I have marked a few stars with those magnitudes. I have also attached screen copies of the USNO chart and USNO data file that is provided with each on-line query.
So, it would seem that the C9.25 at F6.3 with the (older parallel) ST7E can reach mag 20 from the suburban skies of Brisbane – an impressive feat!
This research has made use of the USNOFS Image and Catalogue Archive operated by the United States Naval Observatory, Flagstaff Station. http://www.nofs.navy.mil/data/fchpix/
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