Electronic Telegram No. 175
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
M.S. 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
CBAT@CFA.HARVARD.EDU (science)
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SUPERNOVA 2005cs IN M51
     W. Li, University of California at Berkeley; S. D. Van Dyk,
Spitzer Science Center, California Institute of Technology; and
A. V. Filippenko, University of California at Berkeley, report
that they have isolated a possible progenitor for this young
type-II supernova in Hubble Space Telescope images of M51
(GO/DD program 10452) taken with the Advanced Camera for Surveys
(ACS).  A geometrical transformation between recent KAIT images
of the supernova and the ACS images has yielded the identification
of an object (mag 24.0 +/- 0.2) in the ACS F814W images that is
within the 0".15 uncertainty of the supernova position; this
object was not detected in the F555W images (mag > 25.5).
Assuming low reddening to the supernova [E(B-V) = 0.1 mag; cf.
IAUC 8555] and a true distance modulus to M51 of 29.6 mag
(Richmond et al. 1996, A.J. 111, 327), the object is consistent with
a red supergiant with an approximate absolute I magnitude of -5.8
and colors V-I > +1.4, implying an initial mass for the progenitor
of less than about 10 solar masses.  The supernova occurred in a
crowded field, and there are several other red sources and a bright,
blue, possible compact star cluster within 0".3 of the supernova
location.  High-resolution images of the supernova and a more
thorough analysis are required to verify the identification of
the progenitor.


NOTE: These 'Central Bureau Electronic Telegrams' are sometimes
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                         (C) Copyright 2005 CBAT
2005 July 1                      (CBET 175)               Daniel W. E. Green