Central Bureau for Astronomical Telegrams

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IAUC 7476: 2000dc; C/1999 S4

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                                                  Circular No. 7476
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)
URL http://cfa-www.harvard.edu/iau/cbat.html  ISSN 0081-0304
Phone 617-495-7244/7440/7444 (for emergency use only)

SUPERNOVA 2000dc IN ESO 527-G019
     C. Yu and W. D. Li, University of California at Berkeley, on
behalf of the Lick Observatory Supernova Search (cf. IAUC 6627,
7126), report the discovery with the 0.8-m Katzman Automatic
Imaging Telescope (KAIT) of an apparent supernova on unfiltered
images taken on Aug. 9.3 UT (mag about 16.9) and Aug. 10.3 (mag
about 16.5). The new object is located at R.A. = 20h20m45s.47,
Decl. = -24o07'57".5 (equinox 2000.0), which is 3".5 west and
16".0 south of the nucleus of ESO 527-G019.  A KAIT image of the
same field on Aug. 2.3 showed nothing at the position of SN 2000dc
(limiting mag about 19.0).

     H. Weaver, Johns Hopkins University, and R. West, European
Southern Observatory, on behalf of a large group of collaborators,
report the following results: "Hubble Space Telescope (HST) images
taken during Aug. 5.167-5.396 UT and Very Large Telescope (VLT)
images (image quality about 0".6) taken during Aug. 6.978-6.999
revealed about a dozen active fragments, most of them located
within about 20" of the western tip of the dust tail (cf. IAUC 7474).
The correspondence between fragments in the HST and VLT images is
generally very good, but the brightest fragment in the HST image is
not seen in the VLT image, indicating rapid variability in the
activity levels. The dynamic nature of the fragments was further
highlighted by a dramatic change in the appearance of the fragments
in VLT images taken during Aug. 9.976-9.996, when they were barely
detectable. Although the latter images were taken under mediocre
observational conditions (image quality about 1"-1".3, thin cirrus,
and nearly full moon), that alone seems unlikely to account for the
observed changes. A very preliminary estimate for the R magnitude,
within a circular aperture of radius 0".23, of one well-isolated
fragment is about 24. A completely inactive fragment with a diameter
of 100 meters observed under these conditions (r = 0.79 AU, Delta =
0.69 AU, Phase = 86o) would have R about 25.9 (assuming a 4-percent albedo
and 0.04 mag/deg phase law). We urge ground-based observers to
continue monitoring the comet and to report any unusual changes near
the 'tip', both in brightness and morphology."

                      (C) Copyright 2000 CBAT
2000 August 10                 (7476)           Elizabeth O. Waagen

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