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Robin, Yes you’re right about the nucleus diameter (I was thinking it was around the same as Rosetta’s actual target, 67P, but it is quite a bit smaller. Your calculation for the bare nucleus mag is pretty good. JPL Horizons gives a nuclear mag on Dec 9 of 12.85. I get mags of 11.91V, 11.30R in an 11 arcsec diameter aperture and the R profile is definitely broader than G close in (R is mainly dust, G is mainly gas). I think you are seeing the inner dense dust cloud around the nucleus which is probably around 1.5 mags brighter than the nucleus on its own.
This plot was obtained using a widefield system with a pixel size of 2.77 arcsec.
Great work from all the spectroscopists on this. The Comet Section Director is obviously going to have to learn a bit more chemistry!
Robin. I think the bare nucleus of 46P is only around 4km in diameter so you won’t be seeing anything from that. Even though most people are imaging the green Swan emission lines from gas in the coma there will be a considerable amount of dust close in. The surface brightness profile of the coma is attached. The dust will be significant in the inner part of the coma.
Yes, the “official” recording won’t be much different to that. We’ll just chop out all of the interval stuff and upload the talks as individual items.
Lars. Glad you enjoyed it and found it useful. It’s certainly something that we want to do again when we can.
Hi Ronan. Glad you enjoyed the meeting watching from the west of Ireland. Yes I remember the wonderfully dark skies in Mayo and I hope you’re getting a great view of 46P when the weather cooperates.
We’ll certainly try to do this again when we have the opportunity. I’ve just watched a few clips from the meeting on Youtube and the quality is very good. This was a learning experience for us but it worked well and we had around 30 people watching the livestream.
We could livestream this meeting because that the IoP had the facilities and expertise to provide a very good user experience. This is not the case at our other venues. Hopefully we’ll be back at the IoP soon so that we can do this again and, hopefully, some of the other venues we use would be able to offer this in the future.
Thanks again to the IoP for hosting the meeting and to Hazel Collett for the excellent organisation.
Happy Christmas and look out for that comet (and those meteors and variable stars).
Nick.
Are you using background from PSF or background from aperture? I think you should always use the latter since the PSF background estimator needs a much biffer photometric aperture to work properly. They often give very different magnitude zero points.
George. Congrats on another nice discovery. I’m getting 17.4 unfiltered (UCAC-4 R band) tonight (see attached). I think the photometric apertures that you are using in Astrometrica may be a bit small. This may lead to some problems with it estimating the sky background.
Recent magnitude estimates indicate that this comet is not brightening very quickly and latest estimates put it around mag 9. It will get increasingly difficult to observe as its elongation decreases but please try to get more images and estimates as it heads in to perihelion. There is a good set of images in the Comet Section archive.
Lars, The ephemeris from the MPC that Peter gave is about as good as it gets. Any differences in the 1981 ephemeris will be due to a different epoch (B1950 vs J2000) and fewer observations. I’ve attached an ephemeris from JPL Horizons wich is very similar to the MPC one. I’ve also attached a scan of BAA Circular 615 from 1981 March 4 which includes an ephemeris based on only 12 positions over a short arc so you can compare.
Yes there is. You can see it better in the stack attached. This is stacked on stars so the comet is trailed and the background is not yet sorted but it shows the ion tail going out of the field.
Here’s a quick process of a widefield image I took this morning with Denis Buczynski in northern Scotland. I’ll do a better job of processing this later and put the result on my members page. The galaxy is NGC4753.
David – Great image showing the tail. Denis and I managed to get some astrometry on it this morning but the conditions were poor so our images are rubbish.
Official designation is C/2018 V1.
Probably 7.5 – 8.0 this morning. Any predictions will be very unreliable since it could be in the final stages of a bright outburst or not. Getting up early to observe it is the only way to find out!
Owen. Yes, Andrew Robertson and Peter Carson had a good view through Andrew’s 18-inch telescope at Haw Wood. They commented that the comet was bright and easy.
The latest ephemeris is here using all astrometry I have so far. I’ve done this starting 60 days before now and the positional uncertainties are now quite small. The comet has been at a small elongation for all of this time and was discovered when it was at its largest elongation. This is now decreasing. The comet has a small q (0.39 au) and is brightening rapidly.
Please try to observe this comet at any opportunity.
Nick.
