1 research outputs found
Outgassing Behavior of C/2012 S1 (ISON) From September 2011 to June 2013
We report photometric observations for comet C/2012 S1 (ISON) obtained during
the time period immediately after discovery (r=6.28 AU) until it moved into
solar conjunction in mid-2013 June using the UH2.2m, and Gemini North 8-m
telescopes on Mauna Kea, the Lowell 1.8m in Flagstaff, the Calar Alto 1.2m
telescope in Spain, the VYSOS-5 telescopes on Mauna Loa Hawaii and data from
the CARA network. Additional pre-discovery data from the Pan STARRS1 survey
extends the light curve back to 2011 September 30 (r=9.4 AU). The images showed
a similar tail morphology due to small micron sized particles throughout 2013.
Observations at sub-mm wavelengths using the JCMT on 15 nights between 2013
March 9 (r=4.52 AU) and June 16 (r=3.35 AU) were used to search for CO and HCN
rotation lines. No gas was detected, with upper limits for CO ranging between
(3.5-4.5)E27 molec/s. Combined with published water production rate estimates
we have generated ice sublimation models consistent with the photometric light
curve. The inbound light curve is likely controlled by sublimation of CO2. At
these distances water is not a strong contributor to the outgassing. We also
infer that there was a long slow outburst of activity beginning in late 2011
peaking in mid-2013 January (r~5 AU) at which point the activity decreased
again through 2013 June. We suggest that this outburst was driven by CO
injecting large water ice grains into the coma. Observations as the comet came
out of solar conjunction seem to confirm our models.Comment: 8 pages, 2 figures, 3 table