Hi Charles,

Goodness, sorry to hear about the observatory incident. I live in fear of my scope tearing its cables out during an unattended 3am slew. Lucky so far.

Thanks for sending your image. Looking at a cross-section of a star trail, the FWHM is ~5 pixels, or 6" at 1.21"/pix. Im thinking hard about whether the FWHM of a trail is the same as a point source - I suspect not - I think it will be larger as the peak will be lower, so the FWHMa of your images are probably a little better than this. Nonetheless, this is still a larger figure than most of the images which are showing the contentious distinct point-like features or fragment. I think this is probably why your images dont show them.  In early April I know I was incredibly lucky with the seeing for a number of nights - one of my data sets in C/2019Y4 is actually the sharpest of any I've obtained in the last year, since I started using NINA which reports HFR for each image. Many FWHMa are 2" for my images from the first half of April. I rarely beat this.

While its fun and fascinating to think about what these images mean in terms of chunks of ice and rock rushing around far away, whether or not we can easily interpret them isnt evidence against their being in our images, though it of course should make us careful in our analysis.

I think you're underestimating what small scopes are capable of, especially in this era of low noise CMOS cameras and short subs.

Good to talk and think about these things! Clear skies!

Nick

From: baa-comet@simplelists.com <baa-comet@simplelists.com> on behalf of Charles S Morris - cometguy3783 at yahoo.com <baa-comet@simplelists.com>
Sent: 03 May 2020 19:32
To: baa-comet@simplelists.com <baa-comet@simplelists.com>
Subject: Re: [BAA Comets] C/2019 Y4 (ATLAS) new fragment
 
To Nick and Nick,

I have attached my image.here.

Unfortunately, I am out of service for a few days.  When I opened up last night, a cable that is used to close the roof (and is pulled when the roof is opened) somehow 'grabbed' a connector box that has USB cables from the telescope, camera, and focuser.  The USB box was not plugged into the computer, fortunately.  The USB connector for the telescope was destroyed in the freak accident,  This is an easy fix (hopefully) because it is part of a separate parallel to USB cable.  Anyway, right now I can not control the telescope until the replacement part comes a few days from now.

I have no doubt folks have sent in positions on the fragments - how many fragments by the way?  What I am not sure of is that it is possible to identify individual fragments with small scopes accurately - that is they can get positions but do they really know what the positions are actually of?   Fortunately, I don't do astrometry and that potential mess is not my problem.

I knew when I sent the message that there would be blowback from my comments.  I am waiting for some confirmation observation to prove me wrong.  And Nick (James) I do respect what you do - a lot of good work.

But consider the logic (since one Nick thinks my image may not be up to snuff) - a fragment of the comet would have to be dormant, races out in front of the other fragments, and then lights up so Nick can image it.  (No doubt, it has flared out by now?  Yes?) 

Actually, the part that doesn't make sense is the fragment racing out to the front of the nucleus.  No doubt someone could figure out what the differential velocity would have to be for that to happen.  I am guessing that it is unrealistic.  And why wouldn't there be other fragments in a string, like is often seen?

If I am wrong, I will be happy to eat my words.  At the moment, this new fragment does not pass the smell test - sorry.

Best regards,
Charles  

On Sunday, May 3, 2020, 09:28:18 AM PDT, Nick Haigh <happylimpet@hotmail.com> wrote:


Hi Charles,

Interested to hear your take on things! 

Perhaps you could share your non-detection images? If you can demonstrate the nonexistence of these features, it would be important. I think more likely is that your images are deficient either in depth or resolution to show them. These are not, after all, features that jump out with casual imaging; not that I am suggesting that yours is, but you take my point!

Cheers

Nick
From: baa-comet@simplelists.com <baa-comet@simplelists.com> on behalf of Charles S Morris - cometguy3783 at yahoo.com <baa-comet@simplelists.com>
Sent: 03 May 2020 04:54
To: baa-comet@simplelists.com <baa-comet@simplelists.com>
Subject: Re: [BAA Comets] C/2019 Y4 (ATLAS) new fragment
 
Hi Nick,

I appreciate the fact that you are asking for confirmation of your observation.  I can say that there is no such object on my image taken on May 2.196 UT with my 41 cm SCT + CCD.  I processed my image every possible way and ran brightness profiles through the coma.  Nothing was there.

I have no idea what is on your image.

Now for a reality check - I apologize for this Nick, but a few weeks ago everyone, regardless of instrument size, was claiming to have imaged "the comet and fragment ."  I threw cold water on that and finally, that ended.  Now I have to end this before it starts again.

1) It would take months or years for a fragment to move that far in front of (or any direction from) the main nucleus.  I saw the fragments from Comet West many months after the break-up (through John Bortle's 12" L) and they were still in a tight little cluster.  The differential velocity between fragments simply isn't that great and we are looking at vast distances between the center of the comet and the edge of the coma.  

2) If it was real, there would be a string of fragments and not just one out there by itself.  I suspect that all the fragments are still very close to the center of light in the coma.

3) Unless you have a meter class instrument, you are not going to be able to resolve the fragments.  Everyone, PLEASE stop looking for things that can not reasonably be at the edge of the coma.  You will find them.  I doubt that they are real, but you will find stuff.  Heaven knows people did a few weeks ago.  And none of it was real.

4) Prior to suggesting fragments, I propose that such reports be ignored unless 1) the observers are using meter class or larger telescopes, 2) they have two nights of observations with astrometry proving the unknown object is connected to the comet, or 3) the observations are with HST!

A separate question - who has assigned letters to the various fragments???  I hope it is the HST folks that clearly had 11 fragments.  I have seen at least one assignment of fragments and their distribution of fragments did not agree with the HST image - a small problem.  So who did the assignment?

Sorry to be straightforward and undiplomatic, but I don't want to get people's hopes up that they are going to image something that isn't really possible.

I will be posting my recent images on FB and probably on the comet images group.

Regards,
Charles

On Saturday, May 2, 2020, 03:35:49 PM PDT, Nick James <ndj@nickdjames.com> wrote:


This comet continues to do interesting things!

My image tonight shows a new fragment 20 arcsec west and 9 arcsec south
of the the main nucleus (component B). The new fragment is around mag
18.8. The residual nucleus, component B, is currently around magnitude
15.2. An image showing the fragment is here:


Has anyone else imaged this?

Nick.



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