Electronic Telegram No. 3719
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. M. Lisse, Applied Physics Laboratory, Johns Hopkins University; S. J.
Wolk, Harvard-Smithsonian Center for Astrophysics; D. J. Christian, California
State University, Northridge; K. Dennerl, Max-Planck-Institut fuer
Extraterrestrische Physik; D. Bodewits, University of Maryland; and M. R.
Combi, S. T. Lepri, and T. H. Zurbuchen, University of Michigan, report the
detection of comet C/2012 S1 by the Chandra X-ray Telescope in three
observations of the comet on Oct. 31.302, Nov. 3.083, and Nov. 6.438 UT.
Detections were obtained in both the ACIS-S spectrophotometric (0.3-2.0 keV)
and HRC-I imaging (0.1-10 keV) cameras in 8700- and 3800-s duration exposures,
respectively.  Total count rates of 0.24, 0.36, and 0.30 counts/s were found
for C/2012 S1 by the ACIS-S when the comet was at r = 1.0, 0.94, and 0.87 AU
from the sun, and at Delta = 1.25, 1.17, and 1.08 AU from the earth.  During
this time, C/2012 S1 exhibited a neutral gas-emission rate, Q_gas, of 1 to 3
x 10**28 molecules/s (Dello Russo et al., CBET 3686; Mumma et al., IAUC 9261)
and a moderately low dust-to-gas ratio of about 0.7.  Assuming a 1/Delta
luminosity dependence, the comet's 0.3- to 1.0-keV x-ray luminosity was 3.1,
3.5, and 3.9 x 10^15 ergs/s and its L_x/L_opt ratio was about 0.0001,
typical of the brightest Chandra-detected comets.  The approximately 5' width
of the detected x-ray emission seen on Nov. 3 and Nov. 6 corresponds to an
emitting region about 260000 km in diameter, typical for bright x-ray comets
and consistent with the OH coma radius of > 500000 km detected by SWIFT on
Nov. 7 (see Bodewits et al., CBET 3718).  The relative signal ratio of O VIII/
O VII in the ACIS-S vs. HRC-I cameras flipped between Oct. 31 and Nov. 3/6,
likely due a decrease in the corresponding coronal-source (O^{7+}/O^{6+}) ion
abundance in the solar wind [dominated by wind from a coronal mass ejection
or a coronal hole; cf. Neugebauer et al. 2002, J. Geophys. Res. 107(A12),
SSH 13-1] that impacted the comet on Oct. 31.

     C. Opitom, E. Jehin, J. Manfroid, and M. Gillon, Liege University, report
on the detection of a new outburst of comet C/2012 S1 that started between
Nov. 18.37 and 19.37 UT, in observations made with the robotic TRAPPIST 0.6-m
telescope at the European Southern Observatory at La Silla.  In the following
48 hours, the gas- and dust-production rates multiplied by a factor of about
five.  This is the third outburst detected by the TRAPPIST team after those
of Nov. 4 (CBET 3693) and Nov. 13 (CBET 3711).  The production rates dropped
by a factor of about two during the five nights following the previous
outburst (Nov. 13).  The new maximum was observed on Nov. 21.37 (r = 0.41 AU,
Delta = 0.86 AU), and the following gas-production rates were computed for
10000 km from the comet's nucleus using a Haser Model (V_p = V_d = 1 km/s),
and Af(rho) was measured in the blue continuum at 10000 km:  Q(OH) = 1.08
(+/- 0.58) x 10**29 molecules/s, Q(CN) = 1.60 (+/- 0.18) x 10**27 molecules/s,
Q(C_2) = 2.52 (+/- 0.12) x 10**27 molecules/s, Af(rho) = 5820 +/- 644 cm.
Two bright jets perpendicular to the tail were visible, and there is no
indication yet of splitting or disruption.

     Additional visual total-magnitude and coma-diameter estimates (cf. CBET
3711; an asterisk indicates a magnitude that has been corrected for
atmospheric extinction):  Nov. 15.30 UT, 5.3, 5' (W. Souza, Sao Paulo, Brazil,
10x50 binoculars); 16.22, 5.3, 9' (S. Baroni, Milan, Italy, 20x80 binoculars);
17.22, 5.7, 4' (B. H. Granslo, Roverkollen, Oslo, Norway, 10x50 binoculars;
altitude 9 degrees; bright sky); 18.17, 5.4, 2' (Kazimieras Cernis, Vilnius,
Zirmunai, Lithuania, 7x50 binoculars; altitude 9 degrees); 18.53, 5.4, 3'
(Carl Hergenrother, Tucson, AZ, U.S.A., 10x50 binoculars); 19.18, 5.0*, about
4' (M. L. Paradowski, Lublin, Poland, 7x50 binoculars; twilight; altitude 9
degrees); 19.53, 5.2, 3' (Hergenrother); 20.22, 5.0, -- (J. J. Chambo,
Valencia, Spain, 20x60 binoculars; moonlight; altitude 7 degrees); 20.24, 4.6,
2' (Granslo, 8.0-cm refractor; altitude 6 degrees); 20.86, 3.8*, -- (K.
Yoshimoto, Yamaguchi, Japan, 8x42 binoculars; altitude 9 degrees); 21.25, 3.8,
2' (J. J. Gonzalez, Salamanca, Spain, 10x50 binoculars; 1.5-deg tail;
moonlight); 21.45, 4.0, -- (John E. Bortle, Stormville, NY, U.S.A., 15x70
binoculars; low altitude).


NOTE: These 'Central Bureau Electronic Telegrams' are sometimes
      superseded by text appearing later in the printed IAU Circulars.

                         (C) Copyright 2013 CBAT
2013 November 22                 (CBET 3719)              Daniel W. E. Green