[Iaude] CBET 4840: COMET 88P/HOWELL
quai at eps.harvard.edu
quai at eps.harvard.edu
Sat Aug 29 13:13:25 EDT 2020
Electronic Telegram No. 4840
Central Bureau for Astronomical Telegrams
Mailing address: Hoffman Lab 209; Harvard University;
20 Oxford St.; Cambridge, MA 02138; U.S.A.
e-mail: cbatiau at eps.harvard.edu (alternate cbat at iau.org)
Prepared using the Tamkin Foundation Computer Network
J. Crovisier, P. Colom, N. Biver, D. Bockelee-Morvan, LESIA, Observatoire
de Paris; and I. Cognard, Laboratoire de Physique et Chimie de l'Environnement
et de l'Espace, Universite d'Orleans, report: "While monitoring the 18-cm
lines of OH in comet 88P/Howell at the Nancay radio telescope, we
serendipitously observed the occultation of the radio source PKS 1416-15 by
the comet on Aug. 15.69 UT. This point radio source, which has a flux of
about 2 Jy at 18 cm, was then 2'.2 from the comet nucleus, corresponding to a
projected distance of 125000 km. The 1667-MHz line area was then observed to
be -250 +/- 25 mJy*km/s, enhanced by a factor of 5 with respect to the signal
as averaged for +/- 6 days before/after the event. This can be explained by
the OH maser amplification of the background radio source radiation. The OH
production rate averaged before/after the occultation was estimated to be 3.3
x 10**28 molecules/s. A similar event was observed on 1989 Oct. 13 for comet
C/1989 Q1 (Crovisier et al. 1989, IAUC 4882; Crovisier et al. 1992, A.Ap.
E. Jehin, STAR Institute, University of Liege, reports (together with
Y. Moulane, J. Manfroid, F. Pozuelos, and D. Hutsemekers) that they obtained
narrowband photometry of comet 88P with the robotic 0.6-m "Transiting Planets
and Planetesimals Small Telescope" (TRAPPIST-North) at Oukaimden, Morocco,
on Aug. 17 (with the comet at r = 1.42 AU and Delta = 1.31 AU), using the
HB comet filters (cf. Farnham et al. 2000, Icarus 147, 180) that focus on
seven cometary emissions and four continuum bands. Using a Haser model (with
V_p = V_d = 1 km/s, for 10000 km and correcting for the phase angle) they
computed the dust-production rate proxy (as explained on CBET 4691) by
profile fitting and correcting for the phase angle: A(0)f[rho](R) = 372 +/-
9 cm. They determined the following molecular production rates:
Q(OH) = 2.97 (+/- 0.17) x 10**28 molecules/s, Q(CN) = 4.86 (+/- 0.10) x
10**25 molecules/s, Q(C_2) = 5.59 (+/- 0.12) x 10**25 molecules/s.
Selected recent visual total-magnitude and coma-diameter estimates:
Apr. 15.46 UT, 14.4, 0'.8 (C. Wyatt, Walcha, NSW, Australia, 0.40-m
reflector); 18.48, 13.9, 1' (P. Camilleri, Katherine, NT, Australia, 0.40-m
reflector); May 10.39, 13.6, 0'.8 (Wyatt, 25-cm reflector); 21.87, 13.0,
0'.3 (W. Hasubick, Buchloe, Germany, 44-cm reflector); June 9.48, 12.2, 3'
(Camilleri); 16.37, 11.7, 3' (Wyatt, 25-cm reflector); 20.94, 10.7, 4' (J. J.
Gonzalez, Leon, Spain, 0.20-m reflector); July 12.98, 11.2, 2' (M. Goiato,
Aracatuba, Brazil, 0.22-m reflector); 18.43, 10.6, 3' (Camilleri); 24.91,
10.1, 3'.5 (Gonzalez); 30.37, 10.3, 4' (Wyatt, 25-cm reflector; moonlight);
Aug. 8.98, 10.3, 3' (Goiato); 13.88, 9.4, 7' (Gonzalez); 19.48, 9.3, 4' (K.
Yoshimoto, Yamaguchi, Japan, 20x100 binoculars); 23.92, 9.6, -- (J. G. de S.
Aguiar, Campinas, Brazil, 25x100 binoculars; moonlight); 27.92, 9.4, --
(Aguiar, 0.27-m reflector).
NOTE: These 'Central Bureau Electronic Telegrams' are sometimes
superseded by text appearing later in the printed IAU Circulars.
(C) Copyright 2020 CBAT
2020 August 29 (CBET 4840) Daniel W. E. Green
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