Comet 88P/HOWELL

Crovisier, J. ; Colom, P. ; Biver, N. ; Bockelee-Morvan, D. ; Cognard, I. ; Jehin, E. ; Moulane, Y. ; Manfroid, J. ; Pozuelos, F. ; Hutsemekers, D. ; Wyatt, C. ; Camilleri, P. ; Hasubick, W. ; Goiato, M. ; Gonzalez, J. J. ; Yoshimoto, M. ; Aguiar, J. G. de S. 

Abstract

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. 253, 286)."

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).