Circular No. 6634 Central Bureau for Astronomical Telegrams INTERNATIONAL ASTRONOMICAL UNION Mailstop 18, 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) URL http://cfa-www.harvard.edu/cfa/ps/cbat.html Phone 617-495-7244/7440/7444 (for emergency use only) COMET C/1995 O1 (HALE-BOPP) G. Cremonese, Astronomical Observatory, Padua; H. Rauer, Observatoire de Paris, Meudon; and A. Fitzsimmons, Queen's University, Belfast, on behalf of the European Hale-Bopp Team, report further observations pertaining to the neutral-sodium tail recently discovered in C/1995 O1 (IAUC 6631; c.f. http://ing.iac.es/PR/Caption_ING397.html): "Spectra were obtained on Apr. 19.90 UT with the Utrecht Echelle Spectrograph at the 4.2-m William Herschel Telescope at the Observatorio del Roque de los Muchachos, La Palma, with a 4".0 by 1".1 slit positioned 1.5 deg along the sodium tail at p.a. 56 deg (this position angle being determined by simultaneous imaging with the CoCAM instrument). The location of the slit corresponds to a cometocentric distance of 1.1 x 10**7 km along the tail. A series of spectral windows were observed between 500 nm and 800 nm at a resolution of 7 km/s. In a 15-min exposure, strong Na D lines were detected (their strength relative to the sky lines being approximately 1.3:1), redshifted at a line-of-sight velocity of +105 km/s, which corresponds to a cometocentric velocity of approximately 95 km/s along the tail. The lines are resolved with an intrinsic FWHM of about 11 km/s. These data confirmed that neutral Na is present in the newly-detected third type of cometary tail. Emissions from H2O+, NH2 and C2 (among other molecules) were not detected at this tail position. The same instrumentation was used on Apr. 20.85 UT to obtain spectra at 10" from the nucleus and at 0.7 deg (cometocentric distance 5.0 x 10**6 km) along the Na tail. Once again, Na D-line emission associated with the comet was observed, at cometocentric velocities of 0 and 58 km/s, respectively. From the measured velocity distribution and surface brightness along the tail, it would appear that the data are consistent with a model in which neutral sodium atoms are released from still-unidentified sources within the coma and then accelerated in the antisolar direction by simple fluorescence. At the same time as the Apr. 19.90 spectroscopic data were being secured, CCD imaging was performed by J. Licandro, Instituto de Astrofisica de Canarias, with the 1-m Jacobus Kapteyn Telescope through a narrow-band filter (lambda_0 = 587.7 nm, FWHM = 4.9 nm) and an adjacent continuum filter. A comparison between these images over the 5' field of view did not reveal any features that could be identified as peculiar to neutral Na." COMET 29P/SCHWASSMANN-WACHMANN 1 Visual m1 estimates: Mar. 10.93 UT, 13.5 (K. Hornoch, Lelekovice, Czech Republic, 0.35-m refl.); 28.93, 14.2 (J. Carvajal, Teruel, Spain, 0.44-m refl.); Apr. 1.92, [13.5 (K. Sarneczky, Raktanya, Hungary, 0.44-m refl.). (C) Copyright 1997 CBAT 1997 April 21 (6634) Brian G. Marsden ================== RFC 822 Headers ================== Received: from cfa0.harvard.edu (cfa0.harvard.edu [131.142.10.30]) by cfa.harvard.edu (8.8.5/8.7.3) with SMTP id LAA17861 for ; Mon, 21 Apr 1997 11:51:25 -0400 (EDT) Received: by cfa0.harvard.edu (SMI-8.6/SMI-SVR4) id KAA01538; Mon, 21 Apr 1997 10:55:57 -0400 Date: Mon, 21 Apr 1997 10:55:57 -0400 From: marsden@cfa0.harvard.edu (Brian Marsden) Message-Id: <199704211455.KAA01538@cfa0.harvard.edu> To: iau@gxvg.ast.cam.ac.uk Subject: IAUC 6634: C/1995 O1, 29P