[IAUC] CBET 3693: 20131108 : COMET C/2012 S1 (ISON)

Jue Nov 7 21:01:50 ART 2013

                                                  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 en eps.harvard.edu (alternate cbat en 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