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IAUC 7317: 1999gc; HD 209458; C/1999 S3

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                                                  Circular No. 7317
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/iau/cbat.html  ISSN 0081-0304
Phone 617-495-7244/7440/7444 (for emergency use only)


SUPERNOVA 1999gc IN ANONYMOUS GALAXY
     J. Maza, University of Chile; and M. Hamuy, University of
Arizona, report the discovery by R. Antezana, on a 20-min
unfiltered T-Max 400 film taken by L. Gonzalez on Nov. 10.25 UT
with the University of Chile's Maksutov telescope, of a supernova
(m_pv about 17.5) located at R.A. = 1h05m10s.87, Decl. =
-20o17'48".1 (equinox 2000.0), which is 6".7 west and 10".7 north
of the nucleus of the host galaxy.  The supernova was confirmed by
L.-G. Strolger (University of Michigan) from B,V,R,I images taken
with the Cerro Tololo 1.5-m telescope on Nov. 16.  Hamuy obtained a
spectrum (range 350-900 nm; resolution 0.3 nm) of SN 1999gc on Nov.
19.13 using the New Technology Telescope at the European Southern
Observatory, revealing that the supernova is a type-Ia event, about
3 weeks past V maximum light.  Weak emission lines from the host
galaxy indicate a redshift z = 0.054.  Additional B,V,I images
taken with the Cerro Tololo 0.91-m telescope by Antezana and Hamuy
on Nov. 24.23 yield B = 19.81 and V = 18.65 (+/- 0.05).


HD 209458
     G. Gonzalez, University of Washington, writes that he obtained
differential CCD photometry of HD 209458 during Nov. 22.07-22.35
UT, using the the Manastash Ridge Observatory 0.76-m telescope,
with C. Laws and M. Braunstein.  An 8-nm-side filter centered at
673 nm was used to obtain images every about 3 min.  They detect a
dimming of HD 209458 starting at Nov. 22.28 +/- 0.015 day, but they
did not observe long enough to see last contact, due to the low
altitude of the star.  They estimate that the dimming amounted to
about 0.028 mag (using two comparison stars that were each about 4
mag fainter than HD 209458).


COMET C/1999 S3 (LINEAR)
     Ephemeris extension to IAUC 7285 (elements MPC 36653):

1999/2000   R. A. (2000) Decl.   Delta     r    Elong. Phase    m1
Nov. 28    20 34.26   +53 45.3   1.575   1.908   93.4   31.1   12.8
Dec.  8    20 27.09   +52 55.6   1.685   1.926   88.2   30.8   13.0
     18    20 25.02   +52 45.6   1.788   1.950   84.1   30.1   13.2
     28    20 26.38   +53 15.0   1.882   1.981   80.9   29.4   13.3
Jan.  7    20 30.17   +54 22.3   1.964   2.018   78.8   28.5   13.5
     17    20 35.67   +56 06.3   2.036   2.061   77.6   27.8   13.7

                      (C) Copyright 1999 CBAT
1999 November 24               (7317)            Daniel W. E. Green

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