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Updated data for comet C/2012 S1 (ISON)

1 Oct 2012, 15:22 UTC
Updated data for comet C/2012 S1 (ISON)
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Our team performed follow-up observations of comet C/2012 S1 (ISON) on 2012, Sept. 28.6, remotely through the 2m, f/10 Ritchey-Chretien + CCD Faulkes Telescope North (Haleakala) under good seeing conditions, and a scale of 0.3"/px. After stacking 13 R-filtered exposures, 120-seconds each, comet ISON appears as a pale blob of light, slightly elongated toward the south-west (this is particularly obvious looking at the azimuthal median subtraction rendition). Click on the image below to see a bigger version.The afrho (proxy of dust abundance within the coma) calculation we performed on this dataset, using a few Tycho reference stars having colour indexes close to that of the Sun, provided rather puzzling results: in short, we found a significant variation of the afrho amount, according the dimension of the measurement window (something pretty different from the steady state coma model). We measured an afrho maximum value of 1365 +/- 200 cm, for a corresponding aperture of nearly 16,000 Km in diameter at the comet distance. After this peak, the afrho amount decreases, reaching a minimum of about 900 +/- 200cm for apertures of 50,000 to 60,000 Km. Similar afrho values has been found analyzing CCD images obtained with the 1.5-m f/8 reflector at ...

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