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Comet C/2016 A8 LINEAR

Posted: Mon Aug 15, 2016 8:08 am
by rwilkinson
I read about this comet yesterday on Seiichi Yoshida's website:
Although it's rather faint (12th magnitude), it is at least well-placed in the sky, in Andromeda.
So I decided to have a look for it using the iTelescope T16 in Spain, and set up a job to run on this overnight (around 3am our time).

But then the sky here in Bolton cleared as night fell, so I decided to have a go with my own kit too, and did indeed manage to detect it, before the clouds came over again just before 11pm:
Comet 2016 A8 from Bolton on 14-Aug. 15x 90-sec (unguided) using HX916 on 80mm ED at f/4.6.
c2016a8_14aug.png (193.17 KiB) Viewed 3578 times
Given that there was a bright Moon (low in the South) and I was only using 90-sec exposures (the best I can manage unguided), I was quite pleased with this, my 60th comet. :D

Then this morning I had a look at my data from the iTelescope in Spain:
Comet 2016 A8 from Spain later that night. 3x 200-sec with Takahashi TOA-150 at f/7.3
c2016a8_15aug.png (324.37 KiB) Viewed 3578 times
This showed the comet better (including a hint of the tail), but the tracking wasn't quite right: the mount should have been following the comet's trajectory. And they suffer from aircraft lights too!

Re: Comet C/2016 A8 LINEAR

Posted: Fri Aug 19, 2016 9:33 am
by rwilkinson
I got a clearer picture of the comet last night, despite the moonlight being even brighter than on Sunday. This time I was using an old Starlight Xpress MX716 camera (which I picked up a few months ago for under £100: viewtopic.php?f=9&t=862) fitted with a Meade f/3.3 reducer, on the back of my Celestron C8 SCT. I'd not tried this combination before, but it worked very well.

And as an experiment, I was running without any Light-Pollution Reduction filter, so I could only manage exposures of 60-sec without the background becoming too saturated. And this bright background did show up the vignetting of this optical system all too clearly:
Stack of 40x 1-min from the MX716 with the f/3.3 reducer and no LPR filter. (South is at the top at this stage of the processing).
vignette716.jpg (25.04 KiB) Viewed 3556 times
Of course a proper flat-field would have compensated for this effect, but I found the Local Estimation Gradient Removal in IRIS was a good quick-fix.

So here is my final image, which does show a hint of the comet's tail:
Comet LINEAR on 18-Aug. 40x 1-min using MX716 on C8 at f/3.3.
2016a8_18aug.png (224.61 KiB) Viewed 3556 times
The small gaps in the trails of the background stars are due to me omitting a few of the 1-min exposures which were too badly trailed by my unguided mount, but the large gap was due to an unexpected phenomenon: a major power-cut. It was good news that all the streetlamps went out, but although I was running my mount from a 12V battery and the laptop had its internal battery, I was still using a mains power-unit for the SX camera, so it didn't record any data. :(
And then when the power was restored a couple of minutes later, my neighbour's security light came on, so I had to wait for that to re-set before continuing my captures. :roll:

Re: Comet C/2016 A8 LINEAR

Posted: Mon Sep 12, 2016 8:25 am
by rwilkinson
This comet has certainly faded since I last caught it 3 weeks ago.

Last night I'd set up my Starwave 80ED refractor, mainly to try out my PiGuider autoguiding system (which I'd not used since May), and as the comet was high in the sky (in Vulpecula, near the M27 nebula) it made a good target.

The guiding system worked perfectly, but even after I'd stacked a load of 2-min images I still couldn't see the comet, which is in the ringed area:
Stack of 23x 2-min with HX916 on 80mm ED at f/4.7
wheresthecomet.png (238.94 KiB) Viewed 3449 times
As I couldn't see the comet on any of the individual images, stacking was quite a challenge! I needed to accurately calibrate my image-scale (3.3 x 3.5 arc-sec/pixel) and then calculate the rate of the comet's track across the sky in odrer to determine the parameters for the TRACK2 command in IRIS . This did reveal the comet (at the second attempt):
Comet 2016 A8 on 11-Sep. 23x 2-min with 80mm at f/4.7
c2016a8_11sep.png (304.56 KiB) Viewed 3449 times