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IAUC 9257: C/2012 F6; C/2012 S1

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                                                  Circular No. 9257
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
New postal address:  Hoffman Lab 209; Harvard University;
 20 Oxford St.; Cambridge, MA  02138; U.S.A.
CBATIAU@EPS.HARVARD.EDU           ISSN 0081-0304
URL http://www.cbat.eps.harvard.edu/index.html
Prepared using the Tamkin Foundation Computer Network


COMET C/2012 F6 (LEMMON)}
     M. A. DiSanti, B. P. Bonev, G. L. Villanueva, L. Paganini, and
M. J. Mumma, Goddard Space Flight Center; and E. L. Gibb,
University of Missouri at St. Louis, report detection of parent
volatiles in C/2012 F6 shortly after perihelion, on 2013 Mar. 31
and Apr. 1 UT (when the comet was at r = 0.75 AU, Delta = 1.55 AU;
geocentric velocity +16 km/s), based on high-resolution infrared
spectra acquired with CSHELL at the NASA Infrared Telescope
Facility.  The slit was oriented approximately along the projected
sun-comet direction on Mar. 31, and perpendicular to it on Apr. 1.
Seven gases were detected:  H_2O, OH*** (prompt emission), CO
(measured together with H_2O), C_2H_6, CH_3OH, CH_4 (with OH***),
and H_2CO (with OH***).  Rotational temperatures for H_2O were 80 K
on Mar. 31, and 100 K on Apr. 1.  Using these values, they derived
preliminary production rates (in 10**27 molecules/s) and abundance
ratios (relative to contemporaneously measured H_2O = 100):  Mar.
31, H_2O, 511 +/- 50, 100; CO, 19.5 +/- 2.3, 3.8 +/- 0.6; C_2H_6,
1.69 +/- 0.24, 0.33 +/- 0.06; CH_3OH, 5.77 +/- 0.68, 1.13 +/- 0.16;
CH_4, 3.06 +/- 0.57, 0.60 +/- 0.13; H_2CO, 2.46 +/- 0.45, 0.48 +/-
0.10).  Apr. 1, H_2O, 730 +/- 42, 100; CO, 25.2 +/- 2.3, 3.4 +/-
0.3; C_2H_6, 2.05 +/- 0.21, 0.27 +/- 0.03; CH_3OH, 6.76 +/- 0.51,
0.93 +/- 0.09.  For each date, Q(H_2O) represents the mean from
multiple settings containing water hot-band or OH prompt emissions;
retrieved values among settings were in agreement (within their
1-sigma uncertainties).
     Visual total-magnitude and coma-diameter estimates:  Apr.
10.79 UT, 4.9, -- (D. A. J. Seargent, The Entrance, NSW, Australia,
10x50 binoculars); 16.35, 5.7, 7' (W. Souza, Sao Paulo, Brazil,
11x80 binoculars); May 2.80, 6.7, 4' (K. Yoshimoto, Yamaguchi,
Japan, 20x100 binoculars); 4.15, 6.2, 6' (J. J. Gonzalez, Leon,
Spain, 25x100 binoculars).


COMET C/2012 S1 (ISON)}
     D. Schleicher, Lowell Observatory, obtained limited narrowband
photometry of comet C/2012 S1 on May 4 (when the comet was at r =
3.86 AU) using the Hall 1.1-m telescope at Lowell Observatory,
resulting in the following CN and dust production rates: b Q(CN) =
2.2 x 10**24; Af(rho)(445.0 nm) = 270 cm, with a 62"-diameter
aperture.  The CN value can be used to infer a value for Q(H_2O;
vectorial) at this heliocentric distance of about 6 x 10**26, but
with viable range from 2 x 10**26 to 2 x 10**27.

                      (C) Copyright 2013 CBAT
2013 May 8                     (9257)            Daniel W. E. Green

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