[BAA Comets] Paper on ArXiv today on Comet C/2012 S1 (ISON)

[Richard Miles]

Thanks Jeremy for drawing attention to Toni's paper.

He has put a lot of work into this and there is a lot of good stuff there. 
The various outbursts are well defined in the lightcurve. Its outburst 
behaviour might indeed be characteristic of a relatively slow-rotating 
nucleus (a tentative 3-day period having been seen in the data).

Re. Sections 2.2 and 4.4, I do not quite see how the nucleus size can be 
accurately determined using Lamy's method which was applied to HST data as 
described in:
http://www.aanda.org/articles/aa/pdf/2009/47/aa11462-08.pdf
when the pixel size and PSF in amateur-size instruments (or even the FT) is 
so much larger than in the HST.

A delta function is used and extrapolated to subpixel dimensions. Other 
functions such as with noise calculations (3.6) are invoked but without 
going into any detail. I would like to have seen a worked example and 
whether particular software was used to do the analysis.

Also, not sure how 'ADU residual' is obtained for instance and there is no 
mention of frame zeropoints so we can see how those numbers are converted to 
magnitude.

Taking the 2013 Sep 15 data, the comet is at Delta=2.61 au, r=1.94 au and 
Phase Angle = 19.3 deg. A 1.66-km object having an albedo of 0.04 will 
exhibit a bare nucleus R magnitude of 22.0. At that time the m2 magnitude of 
the comet was about 14.5. So whatever method is used, the extent of the 
extrapolation is very large.

Grateful if anyone else can shed light on this.

Thanks,
Richard




----- Original Message ----- 
From: "Jeremy Shears" <bunburyobservatory at hotmail.com>
To: <comets-disc at britastro.org>
Sent: Wednesday, May 14, 2014 9:16 AM
Subject: [BAA Comets] Paper on ArXiv today on Comet C/2012 S1 (ISON)


> In case of interest:
> Sungrazer Comet C/2012 S1 (ISON): Curve of light, nucleus size, rotation 
> and peculiar structures in the coma and tailToni Scarmato(Submitted on 13 
> May 2014)We present our results for comet (ISON). Our results were 
> obtained with amateur telescopes observing from the ground, before and 
> after the comet had passed conjunction with the Sun in August 2013. We 
> measured a mean radius of 830 +- 245 m, and we have identified a 
> persistent structure in the direction of the sun with a preliminary 
> rotation period of approximately 3 days. In the tail are visible peculiar 
> structures linked to the production of dust by the nucleus. Our data 
> Af(rho) (AHearn et al. 1984), a physical parameter that indicates the 
> amount of dust produced, is approximately 500+-50 cm in the quite phase 
> which means a production Qdust=500kgxsec^-1 equal to 43.2x10^6 kg per day. 
> A considerable amount for a small comet. We have also detected two major 
> outbursts in January, 2013 and November, 2013, and minor outbursts 
> throughou
> t the observation period. Key words: General: general; comets: C2012 S1 
> (ISON), ISON, comets, afrho, photometry of aperture, flux, apparent 
> magnitude, absolute magnitude, fragmentation
>
> See: http://arxiv.org/abs/1405.3112