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IAUC 8556: 2005cs

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                                                  Circular No. 8556
Central Bureau for Astronomical Telegrams
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
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     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 (UCB),
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 < 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.
     Li, Van Dyk, and Filippenko, together with J.-C. Cuillandre,
Canada-France-Hawaii Telescope (CFHT) Corporation; and S. Jha, UCB,
add:  "We have confirmed our identification of the progenitor of SN
2005cs, using CFHT images taken on July 2.28 UT under excellent
seeing conditions (0".7).  Geometrical transformation between the
CFHT images and the HST/ACS images (as mentioned above) yields a
precision of 0.8 ACS pixel for the supernova location on the ACS
images, and our proposed progenitor (above) is the only object
within the error circle.  The position of the progenitor is
measured to be R.A. = 13h29m52s.760, Decl. = +47o10'36".11 (equinox
2000.0) on the mosaic F814W image.  Since only one object exists
within our error circle, and since the limiting absolute V
magnitude in the ACS images is > about -3, we consider it highly
suggestive that this red supergiant is the progenitor of SN 2005cs.
Further analysis is in progress."
     CCD magnitudes for SN 2005cs:  June 30.914 UT, R = 14.0 (R.
Casas, Sabadell, Spain); July 1.86, R_c = 14.1 (T. Scarmato,
Calabria, Italy).

                      (C) Copyright 2005 CBAT
2005 July 3                    (8556)            Daniel W. E. Green

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