FROM YAHOO GROUP
Hi all,
Some info about ISON from our monitoring with the TRAPPIST robotic telescope (using narrow band filters) located in la Silla
While the activity was stable for about a month (we have started our Monitoring on October 12), the gas production rates have finally increased rapidly the last days !
They were multiplied by a factor 2 since about a week, and mostly in the last 3 nights. Note that the AfRHo is still the same (and quite low), this is gas that is coming out (you should see it with V band mag increasing).
Thissurge maybe due to an outburst, or maybe deeper layer of ices are finally now sublimating.
I do not think the comet is disrupting now, as we do not see any special feature in the coma, shell or large dust production in the last nights.
But we have now two nice jets in CN and C2, an indication that we have active region on the comet.
We will continue to monitor the comet with TRAPPIST every night for about 10 more days (visibility is 30 min at the end of the night).
The coming nigths will tell us more about this surge of activity, and maybe the fate of the comet.
Below more technical info submitted for a possible CBET.
Best regards and clear skies,
Emmanuel Jehin
http://www.orca.ulg.ac.be/TRAPPIST/C. Opitom, E. Jehin, J. Manfroid, and M. Gillon, Liège University report that they obtained regularly since October 12, with the robotic TRAPPIST 0.6-m telescope at ESO La Silla Observatory, narrowband photometry of comet C/2012 S1 (ISON). While the comet activity was quite low and stable for about three weeks, the gas production rates are now increasing rapidly, especially since November 3, while the dust production rate has not increased and is still quite low.
The gas production rates were computed at 10.000 km using a Haser Model (Vp=Vd=1km/s), and AfRho was measured in the blue continuum at 10.000 km:
On October 19 (r=1.28 AU, delta=1.60 AU), a typical night during the quiet and nearly constant production rate phase (until October 31), gave : Q(OH) = 5.57E27 +/- 2.12E27 mol/s, Q(CN) = 1.62E25 +/- 0.16E25 mol/s, Q(C2) = 2.54E25 +/- 0.13E25 mol/s and Af(rho)(445.0 nm) = 263 +/- 47 cm
and on November 5 (r=0.89 AU, delta=1.11 AU) : Q(OH) = 8.14E27 +/- 2.31E27 mol/s, Q(CN) = 3.13E25 +/- 0.20E25 mol/s, Q(C2) = 4.90E25 +/- 0.17E25 mol/s, which indicates that the gas production rates increased by a about a factor two in only a few days, while Afrho(445.0 nm) = 175 +/- 27 cm is still low.
These values indicate that ISON has a "typical" composition and has a relatively low dust-to-gaz ratio.
Two jets are now observed at PA=10 and 90 deg in the CN and C2 filters.
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