Cubewanos using long exposures

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Cubewanos using long exposures

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Tuesday, 5 Dec 13

The sky’s clear today and tonight’s forecast is looking very good. The camera desiccant has been recharged, taking advantage of the clear sky, I’ll be targeting TNOs. Air temp is 36°F.

Pluto comes to mind as it’s been sitting there all summer without being viewed. But alas, it’s below the horizon by sunset. Guide 9 indicates that Triton is well clear of Neptune, so what better way to start working Trans Neptunian Objects than checking out Neptune. (For reference, Neptune is 30 AU distant.)

…. And Triton, with 14 arc-seconds separation:

The SBIG isn’t a planetcam for sure, but by processing thirty-four ½ second exposures the separation is very clear. I’m so used to shooting faint stuff with 2X2 binning that it never occurred to me to go to 1X1 high-resolution binning :roll:

While awaiting my targeted TNOs to approach zenith I can’t resist a quick asteroid grab.

251346 is a 2.7 km sized Apollo now .23 AU distant and a relatively brilliant 15.9 magnitude. Since movement is only 1.3’/hr, 3-minute exposures are taken instead of 1-minute exposures in the hope of revealing a faint and yet undiscovered asteroid. Imaged from 18:20 – 18:55 hrs at 3 min, 2X2 binning, -30C cooling, 5 Hz guiding. Frames 1, 4 & 7 show no deviation from the calculated ephemeris (dRA & dDEC both = 0’). With a high S/N averaging 60/1 and asteroid image FWHM of a tight 3.9 arc-seconds I’m showing a magnitude of 15.6 R Since asteroids are frequently potato shaped and since they rotate variation from predicted magnitude is common.

55636 (2002 TX300) is a 1,510 km sized cubewano (classical Kuiper belt object) not yet classified as a dwarf planet. It has a heliocentric radius of 42 AU, a magnitude of 19.6, and an uncertainty level of 1. Because of the great distance involved, speed of apparent motion is a snail-like 0.033’/hr. Imaged from 19:10 – 19:33 at 10 min, 2X2, -30C, 10 Hz. 2 images are taken. I’ll need to return on another night to detect the object by blinking.

55637 (2002 UX25) is a 1,145 km sized cubewano with a heliocentric radius of 41 AU. At 20.0 magnitude it’s the dimmest object I’ll be attempting. Uncertainty level is 3. Motion is 0.0387’/hr. Imaged from 19:48 – 20:21 hrs at 10 min, 2X2, -30C, 1 Hz. A total of 3 images are taken as the first is a discard. Processing must wait later images some other day.

While finishing up on 55637 Alex and his daughter arrive. Now that they’ve seen a TNO it’s time to show my visitors an asteroid.

2010 CL19 is a 1.8 km sized Apollo now 14 million miles distant and 15.7 magnitude. Uncertainty level is 2 and apparent motion is a fast 8.6’/hr. Imaged at 30 sec, 2X2, -30C, 2 Hz. Frames 1, 4 & 7 show dRA = 0.3’ and dDEC = 0’, while measuring a magnitude of 15.4 R (I’d originally been imaging CL19 at 1 minute but the asteroid image was really streaked, and when the dRA showed up I figured that I needed to re-do to confirm the problem as a more appropriate exposure with less streaking.

My guests have to leave now, but before they go we catch a short view of M42 and M45 through the 80mm guide scope at 30X.

136199 Eris is a 11,454 km sized dwarf planet. With a heliocentric radius of 96 AU it’s the most distant dwarf. Uncertainty level is 3. Magnitude is a relatively bright 18.7 mag (I’ve successfully done astrometry on Eris previously). Motion is a miniscule 0.0131’/hr. 2 images are taken from 21:30 – 22:05 hrs at 10 min, 2X2, -30C, 1 Hz. Once again, I’ll need to blink images from a subsequent night to locate/confirm/measure.

Air temp’s now 34°F. I’m in for the night at 22:15.

Conclusions & lessons learned:

What a great night. Alex and his daughter were good company, the sky was very transparent and the seeing was very good. I’ve probably captured all targeted TNOS, but that’s an unknown until I get to blink comparison images.


Wednesday, 4 Dec 2013

The forecast has changed for the better, and last night’s clear sky seems to be continuing into tonight. This is just what’s needed to nail down last night’s TNOs. Air temp is 34°F.

There was a hint of icing on the -30°C chip last night, and it was attributed to having installed the recharged desiccant only a few hours prior to use. But tonight at -30°C there’s heavy frosting on either side of the chip  I hope it’ll be workable.

2009 WE253 is a 1.7 km sized Amor now .5 AU distant and 18.6 magnitude. Motion is 2.8’/hr. The scope’s set up and running early. This asteroid just happened to be close to zenith at dinner-time and there was no reason to let the camera sit idle. Imaged from 17:30 – 18:00 at 2min, 2X2, -30C, 2 Hz. Frames 1, 8 & 15 show no deviation from calculated ephemeris.

55637 (2002 UX25) is the 20.0 magnitude cubewano from last night Imaged from 18:35 – 18:58 at 10 min, 2X2, -30C, 10 Hz. 3 images are taken. S/N ranges from 5/1 on Dec 3 to 10/1 tonight. FWHM is tight for both nights running around 3.5” Stacking 2 images from last night and 3 images tonight, astrometry shows dRA & dDEC = 0’

But wait, there’s more! Perhaps a half-dozen other asteroids show up in the long exposure deep imaging from 55637. And some show in both night’s images.

42046 is a 5.7 km sized asteroid now 17.9 mag and 1.1 AU distant. Motion is a normally undetectable 14”/hour The ephemeris RMS residual is 0.54” dRA & dDEC = 0’

191832 is a 4.6 km sized asteroid now 19.9 mag and 1.8 AU distant. Motion is 0.31’/hr. Stacking, the two frames from last night show dRA & dDEC = 0’, tonight’s 3 frames show the asteroid to be right on the edge of a star, and just about off the FOV. So it goes unreported.

42751 is a main belt asteroid now 19.2 mag and 1.9 AU distant. Motion is 0.29’/hr and RMS is 0.51” Stacking last night’s 2 images and then tonight’s 3 images shows dRA & dDEC = 0’.

55636 (2002 TX300) is the 19.6 magnitude cubewano from last night Imaged at 10 min, 2X2, -30C, 10 Hz. 2 images are taken. Since 10 minute images pick up a number of gamma ray hits last night’s 2 images and this night’s 2 images are stacked. Astrometry of the two resultant images shows no deviation from calculated ephemeris. Being the brightest of the TNOs being imaged, S/N averages 12/1 and FWHM is averages only 3”

136199 Eris is imaged 4 times at 10 min, 2X2, -30C, 1 Hz. (I was called away for a bit and captured more images than needed.) Only one image from Dec 3rd is usable, but the 10 minute exposure is overkill and in the single frame Eris has a strong S/N of 12.4 and a good 4.2 FWHM. Using the single frame from Dec 3 and a stack of 4 from tonight, dRA & dDEC = 0’

Eris also has a couple of guest asteroids in the image set.

46642 is a 7.6 km sized main belt asteroid 19.6 mag and 2.2 AU. Motion is 0.13’/hr and RMS is 0.54”.

26073 is a 13.2 km sized main belt asteroid 18.6 mag and 2.3 AU distant. Motion is 0.21’/hr and RMS = 0.53”. Again both frames from Dec 3 are usable here, so using a 2X stack from last night and the 4X stack from tonight, dRA & dDEC = 0’.

In at 21:50 hrs. Air temp is 32°F. 17 observations are promptly transmitted to the MPC.

Conclusions & lessons learned:

Wow, what a great 2-night session! When I started out on Dec 3 the Dec 4 forecast wasn’t workable. And 2 nights were necessary for these slow moving cubewanos. So luck was running good. A week or two of cloud, and the first image set is wasted.

I’ve done sequential night astrometry rarely, and the deepest the camera’s gone was 20.1 magnitude, so these results are most satisfying.

We’re into clear winter sky, and it’s great.

hgp logged 20:23 hrs., 5 Dec 2013
Pete P.