Hi Richard,

Here you go. The star chosen is at:

RA: 06:54:42.68 Dec: +29:11:57.2

It has a very different profile to the comet but I get 17 arcsec
diameter to the same threshold as the comet (the examples are from the
Nov 24 image). A linear fit to the measured diameters gives:

	dia = -110.64 + 5.81 * date [arcsec]

and this crosses the 17 arcsec line at 2022 Nov 21.99. This is
consistent with your estimate and fits the magnitude data we have from
Patrick.

Nick.

On 26/11/2022 23:29, Richard Miles - rmiles.btee at btinternet.com (via
baa-comet list) wrote:
>
> Interesting  numbers indicating a linear expansion rate, Nick.
> Can you  now use  Comphot to obtain the diameter of a mag 11.9R star in
> normal seeing? Then extrapolate your coma diameters back to that size to
> give an extrapolated start time for the cryo-eruption.
> Cheers, Richard
> ------ Original Message ------
> On  Saturday, 26 Nov, 22 At 22:22, Nick James<ndj@nickdjames.com> wrote:
> I get the following coma diameters from comphot:<br>
> <br>
> 2022-11-22.9    23 arcsec<br>
> 2022-11-23.9    28 arcsec<br>
> 2022-11-24.9    34 arcsec<br>
> 2022-11-25.9    40 arcsec<br>
> <br>
> At the comet's distance of 5.3 au, one arcsecond corresponds to around
> 3,800 km. The observed radius is expanding at around 3 arcsec/day which
> implies an average expansion velocity of around 130 m/s.<br>
> <br>
> The attached animation shows the expansion. The field of view is 2.4
> arcmin square which corresponds to approx. 550,000 km at the comet.<br>
> <br>
> Nick.<br>
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