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IAUC 6234: C/1995 O1; 73P; V705 Cas

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IAUC number

                                                  Circular No. 6234
Central Bureau for Astronomical Telegrams
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
Phone 617-495-7244/7440/7444 (for emergency use only)

     H. E. Matthews, Joint Astronomy Centre, Hilo, and Herzberg
Institute of Astrophysics, Ottawa; and D. Jewitt and M. C. Senay,
University of Hawaii, communicate:  "We have detected the 230-GHz
CO 2-1 rotational line in C/1995 O1, using the 15-m James Clerk
Maxwell Telescope on Mauna Kea on Sept. 5, 7, 19 and 20 UT.
Preliminary measurements of the Sept. 19 data yield line area 0.041
+/- 0.006 K km sE-1 and peak temperature 0.08 K.  The line center
is blueshifted by 0.35 +/- 0.05 km/s with respect to the
instantaneous geocentric velocity, indicating preferential sunward
ejection of gas from the nucleus.  Similar blueshifts were observed
on the other three nights.  Assuming a kinetic temperature of 10 K
(as deduced for CO in 29P/Schwassmann-Wachmann 1 at a similar
heliocentric distance; cf. IAUC 5929), we infer a CO production
rate of 700 kg/s at r = 6.7 AU.  The CO is presumably responsible
for the creation of the extended dust coma seen in C/1995 O1, and
thus for the overall brightness of this comet at large heliocentric
distances.  We expect C/1995 O1 to continue as a CO-driven comet
until water sublimation dominates the volatile production at about
3.5 AU (summer 1996)."
     Z. Sekanina, Jet Propulsion Laboratory, has used the above
production rate to calculate a correspondence to a sublimation area
of 5 kmE2 if near the sub-solar point.  This in turn suggests, if
only 1 percent of the nucleus were active, that the nucleus' size
need not be larger than 10-15 km.

     Total visual magnitude estimates suggest that this comet is
indeed in outburst (cf. IAUC 6215, 6227):  Sept. 17.09 UT, 8.3: (A.
Hale, Cloudcroft, NM, 0.2-m reflector); 18.43, 8.3 (J. Kobayashi,
Kumamoto, Japan, 0.41-m reflector; 4' coma); 21.13, 8.3: (C. S.
Morris, Pine Mtn. Club, CA, 0.26-m reflector; low altitude; 30'
tail in p.a. 110 deg).

     A. Retter and E.M. Leibowitz, Wise Observatory, Tel Aviv
University, report that observations of V705 Cas (N Cas 1993) over
ten nights in Aug. and Sept. with the CCD camera (+ I filter) yield
a light curve that shows clear periodic oscillations with a peak-
to-peak amplitude of 0.05 mag and period 0.2280 +/- 0.0005 day.

1995 September 21              (6234)            Daniel W. E. Green

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