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IAUC 6318: C/1996 B2; GRO J1744-28

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                                                  Circular No. 6318
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. Matthews, Joint Astronomy Centre, Hilo, and Herzberg
Institute of Astrophysics, National Research Council of Canada; and
M. Senay and D. Jewitt, University of Hawaii, report the detection
of HCN (4-3) emission from comet C/1996 B2 at the James Clerk
Maxwell Telescope on Mauna Kea:  "Observations on Feb. 10.7 UT show
the line at -58.05 +/- 0.05 km/s, with peak antenna temperature
0.33 K and area 0.40 +/- 0.03 K km/s.  The geocentric radial
velocity of the comet was -58.01 km/s.  The line width (1.1 +/- 0.1
km/s) indicates expansion of the coma gases at 550 m/s.  Assuming a
kinetic temperature of 15 K (30 K), we estimate HCN production
rates log Q(HCN) = 26.26 (25.93).  This is comparable to the HCN
production rate in 1P/Halley at 1.65 AU inbound (Schloerb et al.
1987, A.Ap. 187, 475).  The ratio of the HCN to OH production rates
(cf. IAUC 6311) is about 0.004.  Within the uncertainties due to
modelling and to possible temporal variability, this ratio is
consistent with the value measured in 1P/Halley at perihelion."
     R. West, European Southern Observatory (ESO), writes that a
15-min CCD exposure obtained by F. Patat on Feb. 16.35 UT with the
Danish 1.54-m telescope (+ DFOSC + R filter) shows two broad tails
that can be followed from about 3' from the point of maximum light
out to 10' at the CCD frame's border.  The stronger of the two
tails has comparatively straight, sharp edges at p.a. 296 and 286
deg (i.e., in the general antisun direction) and shows signs of
internal structure ('streamers'); this is probably an ion tail
(despite the filter).  The other tail is broader, with rather
diffuse structure and undefined edges near p.a. 275 deg.  Spectra
obtained by Patat on Feb. 16.4 (same telescope) and by E.
Cappellaro on Feb. 19.4 (ESO 1.52-m telescope + Boller & Chivens
spectrograph) are very similar to that obtained at La Silla on Feb.
8.2 (IAUC 6306), except that on Feb. 19.4 the CN (1,0) band at
917.0 nm is visible."

GRO J1744-28
     M. C. Miller, University of Chicago, reports that the right
ascension of 'star a' as given on IAUC 6315 (line 23) should read
R.A. = 17h44m36s.72.
R. Rutledge and R. Hunstead alerted Vanden Berk et al. that
'star a' lies closest to 'star C'.

                      (C) Copyright 1996 CBAT
1996 February 20               (6318)            Daniel W. E. Green

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