Comet C/2012 S1 (Ison)
Opitom, C.; Jehin, E.; Manfroid, J.; Gillon, M.; Coulson, I. M.; Milam, S. N.; Villanueva, G. L.; Charnley, S. B.; Disanti, M. A.; Mumma, M. J.; Kuan, Y.-J.; Remijan, A. J.
Central Bureau Electronic Telegrams, 3693, 1 (2013). Edited by Green, D. W. E.
C. Opitom, E. Jehin, J. Manfroid, and M. Gillon, Liege University, report that they obtained narrowband photometry of comet C/2012 S1 regularly since Oct. 12 with the robotic TRAPPIST 0.6-m telescope at the European Southern Observatory, La Silla. While the comet activity was quite low and stable for about three weeks, the gas production rates have increased rapidly since Nov. 3, while the dust-production rate has not increased and is still quite low. The gas-production rates (Q) were computed at 10000 km using a Haser model (Vp = Vd = 1 km/s), and Af(rho) was measured in the blue continuum at 10000 km. On Oct. 19 (r = 1.28 AU, Delta = 1.60 AU), a typical night during the quiet and nearly constant production-rate phase (until Oct. 31), the data yield Q(OH) = 5.57 (+/- 2.12) x 10**27 molecules/s, Q(CN) = 1.62 (+/- 0.16) x 10**25 molecules/s, Q(C_2) = 2.54 (+/- 0.13) x 10**25 molecules/s, and Af(rho) = 263 +/- 47 cm at 445.0 nm; on Nov. 5 (r = 0.89 AU, Delta = 1.11 AU), Q(OH) = 8.14 (+/- 2.31) x 10**27 molecules/s, Q(CN) = 3.13 (+/- 0.20) x 10**25 molecules/s, and Q(C_2) = 4.90 (+/- 0.17) x 10**25 molecules/s, which indicates that the gas-production rates increased by about a factor of two in a few days, while Af(rho) is still low (175 +/- 27 cm at 445.0 nm). These values indicate also that C/2012 S1 has a "typical" composition and has a relatively low dust-to- gas ratio. Two jets are now observed at p.a. 10 and 90 deg in the CN and C_2 filters.