Circular No. 6631
Central Bureau for Astronomical Telegrams
Mailstop 18, 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)

     G. Cremonese, Astronomical Observatory, Padua, on
behalf of the European Hale-Bopp Team, reports the detection of
an extensive neutral Na tail structure associated with this comet:
"The structure is visible on images obtained by D. Pollacco, Isaac
Newton Group, with the wide-field CoCAM instrument (aperture 50 mm,
2k by 1k EEV CCD, 26"/pixel) at the Observatorio del Roque de los
Muchachos, La Palma.  The following description is based on two 10-min
exposures obtained through an Na D filter on Apr. 16.88 UT under
mediocre sky conditions.  The filter (lambda_0 = 589.2 nm,
FWHM = 2.1 nm) has no leak at the 0.02-percent level over the entire
sensitivity range (300-1100 nm) of the CCD.  The images display two
main tails.  The first is a very linear feature 6.6 deg long and less
than (or equal to) 10 arcmin wide with parallel edges over its entire
length and a very sharp south edge at p.a. 52 deg (3 deg north of the
projected antisolar direction).  The second is a broad diffuse northern
tail extending to the edge of the frame, i.e., to more than 6.5 deg.
While the second tail coincides with the dust tail as seen in an adjacent
continuum filter, the first tail has no such counterpart, and we
identify it as a neutral Na tail.  In particular, near-simultaneous
imaging with an H2O+ filter (lambda_0 = 619.3nm, FWHM = 4.5 nm) displays
an ion tail of entirely different and more complex morphology with a main
ray at p.a. 46 deg.  We believe that this is the first clear separation
of a neutral tail of a comet from the dust and ion tails.  The existence
of this third type of cometary tail was confirmed in additional CoCAM
images obtained on Apr. 17.8 UT."

GRB 970228
     M. R. Metzger, J. L. Cohen, J. P. Blakeslee, S. R. Kulkarni,
S. G. Djorgovski and C. C. Steidel, California Institute of Technology;
and D. A. Frail, National Radio Astronomy Observatory, report:
"Moderately deep images of the region near the optical variable reported
on IAUC 6584 were obtained on Apr. 5.24 and 6.27 UT with LRIS on the
Keck II 10-m telescope.  The faint source noted by Groot et al. and by
Metzger et al. on IAUC 6588 and observed later by HST (Sahu et al., IAUC
6606, 6619) was measured in a combined image (15 min total exposure time)
at R = 24.9 +/- 0.3.  In the combined image (with seeing 0".7 FWHM), the
source does not appear significantly extended.  Direct comparison with
the Mar. 6.32 image (Metzger et al., IAUC 6588) indicates that the total
R magnitude has faded by 1.0 +/- 0.4 mag and that the component causing
the earlier images to appear extended has faded below detection level."

                      (C) Copyright 1997 CBAT
1997 April 18                  (6631)              Brian G. Marsden
================== RFC 822 Headers ==================
Received: from ( []) by (8.8.5/8.7.3) with SMTP id KAA28617 for ; Fri, 18 Apr 1997 10:29:04 -0400 (EDT)
Received: by (SMI-8.6/SMI-SVR4)
	id KAA26170; Fri, 18 Apr 1997 10:28:44 -0400
Date: Fri, 18 Apr 1997 10:28:44 -0400
From: (Brian Marsden)
Message-Id: <>
Subject: IAUC 6631: C/1995 O1, GRB 970228