You can find Ferrín's work in the arXiv and on his website. Ferrín used his concept of Secular Light Curves of comets (SLCs) to determine the brighness history of ISON. Using three independent sets of published brightness measurements for ISON, he found all of them exhibit a Slope Discontinuity Event (SDE) at a distance of 5.1 AU, followed by an u-shaped dip in the lightcurve. After that, the comet failed to increase it’s brighness as it continued to approach the sun. In fact, Ferrín claims the comet is actually loosing brightness since the last few days of september.
|SLC of comet ISON. A slope Discontinuity Event appears at -5.1 AU followed by an u-shaped dip and a reduced increase in brightness thereafter. The last three dataponts indicate a sharp drop in brighness at the end of September. Credit: I. Ferrín|
Ferrín’s bold conclusion: “In the view of the evidence, there is a 100% probability, that comet ISON is turning off or disintegrating.”
Reactions to this claim among experts are mostly negative. They spot serious flaws in Ferrín’s analysis. First, the assertion that ISON is loosing brighness (0.5mag in the last three days of september) strongly contradicts other observations. There are reports the comet actually gained 1.0mag within the last days. On my own images, taken on Sep. 28 and Oct.2, respectively, no apparent decrease in brightness is visible (however, taken with simple amateur equipment and partially under poor observing conditions, you shouldn’t rely too much on these). Comet expert Burkhard Leitner doesn't take no stock in Ferrín's analysis: "Visual observations say: all is well with ISON!"Secondly, both Hönig and Tabur disintegrated much closer to the sun than where ISON is right now. ISON’s SDE occured far outside the frost line, the ones experienced by Hönig and Tabur at around 1.2 AU. This is well within the zone where water sublimates due to the increased solar radiation. It is obvious that one must assume totally different physical processes at work here.
The coming days will show if Ferrín is correct. The amateur astronomer in me sincerely hopes he is not!