Electronic Telegram No. 3693 Central Bureau for Astronomical Telegrams INTERNATIONAL ASTRONOMICAL UNION CBAT Director: Daniel W. E. Green; Hoffman Lab 209; Harvard University; 20 Oxford St.; Cambridge, MA 02138; U.S.A. e-mail: cbatiau@eps.harvard.edu (alternate cbat@iau.org) URL http://www.cbat.eps.harvard.edu/index.html Prepared using the Tamkin Foundation Computer Network COMET C/2012 S1 (ISON) 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. I. M. Coulson, Joint Astronomy Centre (JAC), Hilo; S. N. Milam, G. L. Villanueva, S. B. Charnley, M. A. Disanti, and M. J. Mumma, Goddard Space Flight Center (GSFC), NASA; Y.-J. Kuan, National Taiwan Normal University; and A. J. Remijan, National Radio Astronomical Observatory (NRAO), report the detection of HCN (J=4-3) in comet C/2012 S1 from the James Clerk Maxwell Telescope (JCMT) on Mauna Kea on Oct. 4.9 UT, when the comet was at heliocentric and geocentric distances of r = 1.58 AU and Delta = 2.03 AU, respectively. Spectra were taken over a 3-hr period (for program m13bi07) with the HARP B-band array receiver, and they show an emission line at the expected velocity (+/- 0.1 km/s) of peak strength 38 mK (Ta*) above the baseline noise of 10 mK per 1 km/s, and of FWHM 0.9 +/- 0.2 km/s. The derived HCN production rate is (3.2 +/- 0.8) x 10**25 molecules/s. Similar JCMT measures of HCN were taken over a total of 4 hr on Nov. 1.7 by the above authors (Coulson et al.), and (contiguously) by K. Meech, J. Keane, B. Yang, T. Riesen, H. Hsieh, and T. Owen (University of Hawaii), when C/2012 S1 was at r = 0.99 AU and Delta = 1.22 AU. The combined data show a line of peak 34 mK (above the noise level of 13 mK), implying a production rate of Q(HCN) about (1.5 +/- 0.6) x 10**25 molecules/s. Supporting observations were also conducted by A. J. Remijan, NRAO; A. Gicquel, S. N. Milam, M. A. Cordiner, S. B. Charnley, and G. L. Villanueva, GSFC, NASA; and I. M. Coulson, JAC, and detected the F=2-2 hyperfine transition of the J=3/2 level of OH near 1667.359 MHz at the NRAO Green Bank Telescope on Nov. 5.46 (under the program GBT/13B-200). At this time, the comet was 0.9 AU from the sun and 1.12 AU from the earth. The OH fitted-line parameters yield a peak brightness of -0.032 K, a line width of 1.37 km/s, and an integrated intensity about 0.044 K km/s for a 3-sigma detection in less than 45 min. Following Tacconi-Garman et al. (1990, Ap.J. 364, 672) and Schleicher and A'Hearn (1988, Ap.J. 331, 1058), the production rate of OH is Q(OH) about 6.52 x 10**27 molecules/s. Measurements reported here are slightly lower than those reported from recent infrared observations in IAUC 9261 and CBET 3686. NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2013 CBAT 2013 November 8 (CBET 3693) Daniel W. E. Green