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IAUC 8385: 2004dj

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                                                  Circular No. 8385
Central Bureau for Astronomical Telegrams
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
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SUPERNOVA 2004dj IN NGC 2403
     It has been noted by several contributors that star 96 of
Sandage (1984, A.J. 89, 630; B = 18.55, V = 18.31) is close to that
the position of SN 2004dj (cf. IAUC 8377, 8379).  H. Yamaoka,
Kyushu University, remarks that star 96 was questioned by Sandage
and resolved by Larsen (1999, A.Ap. Suppl. 139, 393) to be a young
massive cluster.  He adds that, at the distance of NGC 2403, 1"
translates to 15 pc (as large as the scale of young clusters), and
Larsen gave the effective radius of this cluster (n2403-2866) as
4.3 pc, so that the nature of this source is necessarily uncertain.
     J. Maiz-Apellaniz, Space Telescope Science Institute (STSI),
writes that Sandage's star 96 appears to be pointlike in the
H_alpha image (not continuum-subtracted) obtained by Matonick et
al. (1997, Ap.J. Suppl. 113, 333, Fig. 5a) but was not identified
as an H II region by Sivan et al. (1990, A.Ap. 237, 23), indicating
that Matonick et al. simply detected the R-band continuum.  Based
on these data and on a distance to NGC 2403 of 3.30 Mpc
(Karachentsev et al. 2004, A.J. 127, 2031), star 96 appears to be a
very bright (M_V < -9.3) blue supergiant.  Alternatively, the
progenitor could have been a red supergiant, in which case it must
have been a member of a multiple system or a very compact cluster
that included very bright blue stars.  If the progenitor is indeed
a late-B/early-A supergiant, the color (B-V = +0.24) measured by
Sandage would be compatible with the value E(B-V) about 0.18
measured by Patat et al. (IAUC 8378).
     H. E. Bond and M. H. Siegel, STSI, report that the site of SN
2004dj was imaged on three nights in 1999 January with the Kitt
Peak 4-m telescope (+ Mosaic camera) and on six nights in 1998-
1999 with the Kitt Peak 0.9-m telescope.  Recent CCD frames
showing the supernova (provided by Y. Lipkin, D. Maoz, E. Ofek,
and D. Poznanski of Wise Observatory; R. Arbour of South Wonston,
Hampshire, England; D. Bishop of Hilton, NY; and O. Nielsen of
Rijswijk, The Netherlands), when compared with 1999 4-m-telescope
frames, indicate that SN 2004dj is within 0".3 of Sandage's star
96, and no other star visible in the 4-m-telescope frames is as
close to the supernova position.  Star 96 is one of the brightest
blue supergiants known in NGC 2403; the 0.9-m-telescope CCD frames
yield V = 17.93 and B-V = +0.17.  Humphreys and Aaronson (1987,
A.J. 94, 1156) obtained spectra of star 96 and classified it as
having a composite spectrum with an integrated early-A type but
with He I lines, suggesting the presence of some B stars, as well;
the object appears slightly nonstellar on the 4-m-telescope frames
in 0".9 seeing.

                      (C) Copyright 2004 CBAT
2004 August 10                 (8385)            Daniel W. E. Green

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