Observations of sodium in the coma of Comet C/2012 S1 (ISON) during outburst

Prior to disintegration near its 2.7 R⊙ perihelion, the dynamically new Comet C/2012 S1(ISON) briefly exhibited resonantly scattered sodium emission at the 5890 Å and 5896 Å D lines. In this work, we report a rapid increase in sodium production of >3× between observations made only one day apart and the first observations of cometary sodium during an outburst. Mean Na production is estimated at 1.6 ± 0.3 × 1023 atoms s−1 on UT 19.5 Nov 2013 and 5.8 ± 1 × 1023 atoms s−1 on UT 20.5. At a heliocentric distance of 0.44 AU, the anti-sunward Na tail was detected >106 km from the nucleus. Surprisingly, these production rates are well below those of any previously determined when Na is seen from a comet. Accurately reproducing the emission in the Na tail on UT 20.5 Nov 2013 requires a source near the nucleus that varies with time due to the outburst. Data prior to outburst one day earlier can be reproduced if nearly half of total sodium production is attributed to an extended source such as dust grains. This suggests sources of sodium vapor in cometary coma are sensitive to the dust to gas ratio.