Central Bureau for Astronomical Telegrams
IAUC 6372: C/1996 B2
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Circular No. 6372
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
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)
BMARSDEN@CFA.HARVARD.EDU or DGREEN@CFA.HARVARD.EDU (science)
Phone 617-495-7244/7440/7444 (for emergency use only)
COMET C/1996 B2 (HYAKUTAKE)
D. Schleicher, Lowell Observatory, communicates: "Narrowband
photometry of comet C/1996 B2 was obtained by D. Osip and S.
Lederer (University of Florida) using the 0.79-m telescope at
Lowell Observatory on Mar. 23.2-23.5 UT (r = 1.08 AU), Mar. 24.2-
24.5 (1.06 AU), and Mar. 25.1-25.2 (1.05 AU). Mean Haser-model
production rates for the three dates, respectively, were: log
Q(OH) = 29.17, 29.18, and 28.93; log Q(CN) = 26.69, 26.67, and
26.60; log Q(C2) = 26.86, 26.84, and 26.78. The dust-production
rates were log [Af(rho)] = 3.91, 3.82, and 3.75. Additional
photometry was obtained by R. Millis, D. Schleicher, and L.
Wasserman using the Hall 1.07-m telescope at Lowell Observatory on
Mar. 29.1-29.3 (0.96 AU) and 30.1-30.2 (0.94 AU). Production rates
for these dates were: log Q(OH) = 28.88 and 28.89; log Q(CN) =
26.56 and 26.58; log Q(C2) = 26.73 and 26.77; and log [Af(rho)] =
3.80 and 3.85. Combining these results with those previously
obtained (cf. IAUC 6344) indicates that production was
systematically high on Mar. 23 and 24, particularily for OH, and
returned to near-baseline slopes on the Mar. 25, 29, and 30. The
high values on Mar. 23 and 24 may be related to the 'luminous
knots' reported by Lecacheux et al. (IAUC 6354) on Mar. 23.9-24.2.
Well-defined periodic brightness variations were observed on all
five nights for all species, with a typical amplitude in the log of
about 0.1 each night. Single-peaked lightcurves with periods of
about 6.25 or 8.55 hr are viable, while double-peaked lightcurves
with periods of 9.80, 12.45, 13.0, or 17.2 hr are also acceptable.
Periods shorter than about 5 hr are ruled out. The single-peaked
periods are slightly longer than the periods proposed by Lecacheux
et al. (cf. IAUC 6354). Narrowband CCD imaging by D. Schleicher,
R. Millis, and L. Wasserman using the Hall telescope on Mar. 23,
24, and 25 shows distinct morphological structure varying on a
timescale of well less than 1 hr. Preliminary analysis indicates
the morphology repeats with a period of between 6.0 and 6.4 hr
within an individual night, while the structure does not repeat for
any other period less than 10 hr. The imaging results, combined
with the lightcurve results, strongly imply that the comet has a
rotation period of about 6.25 hr and that a single active region
controls the photometric variations."
Total visual magnitude estimates: Apr. 2.81 UT, 2.2 (H.
Luethen, Hamburg, Germany, 10x50 binoculars); 3.99, 2.1 (R. J.
Bouma, Groningen, Netherlands, naked eye; tail 18 deg long; during
total lunar eclipse); 4.00, 2.3 (J. D. Shanklin, Brinkley, England,
naked eye; tail 7 deg long in p.a. 44 deg).
(C) Copyright 1996 CBAT
1996 April 4 (6372) Daniel W. E. Green
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