Central Bureau for Astronomical Telegrams
IAUC 5739: 1993J
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Circular No. 5739
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
Telephone 617-495-7244/7440/7444 (for emergency use only)
TWX 710-320-6842 ASTROGRAM CAM EASYLINK 62794505
MARSDEN@CFA or GREEN@CFA (.SPAN, .BITNET or .HARVARD.EDU)
SUPERNOVA 1993J IN NGC 3031
R. M. Humphreys, G. S. Aldering, C. O. Bryja and P. M. Thurmes,
University of Minnesota, communicate: "We have a probable identification
of the progenitor star from scans of U,B,V and R Kitt Peak 4-m
prime-focus plates with the Automated Plate Scanner at the University
of Minnesota. These plates were originally obtained on 1982 Mar. 21-23
by Humphreys and were scanned for a stellar content study of M81 by
Zickgraf and Humphreys (1991, A.J. 102, 113). Inspecting these scans
and using the astrometric solution from the above survey, we find a mag
21 star at R.A. = 9h51m19s.2s, Decl. = +69D15'26".5 (equinox 1950.0), in
agreement with the supernova position on IAUC 5731. As additional
confirmation of this identification, we used an I-band CCD image of
SN 1993J, made available by M. Richmond over internet, to measure the
positions of six reference stars in the immediate vicinity of SN 1993J
using imexamine in IRAF. The corresponding positions on the 4-m plates
were determined from the isodensity scans made with the APS. A linear
transformation between these sets of coordinates was then calculated. The
root-mean-square uncertainty of the transformation was less than 0".15
in each coordinate. The candidate progenitor has a position on all four
4-m plates that is within 0".15 of the position of SN 1993J on the CCD
frame. The magnitudes measured from these plates are: V = 20.8 +/- 0.1,
B = 21.4 +/- 0.2, R = 19.9 +/- 0.2 and U = 21.7 +/- 0.2. Our V is 0.8
mag fainter than reported by Perelmuter on IAUC 5736. Thus the star
may be variable; all of our photometry is from plates obtained within
two days of each other. The colors are consistent with the candidate
progenitor being a highly reddened late A or early F-type supergiant.
We have looked for evidence of blending in our images, but as well as
can be determined from our plates (1"-2" seeing) the image is isolated.
The star is in an association of faint blue stars as seen on our U and
B plates. It is also on the inside edge of a prominent dust lane or
cloud, so reddening should be considered when interpreting the photometry."
M. Richmond, Princeton University, reports: "The progenitor
of SN 1993J could not have been a blue supergiant. Images of
M81 obtained in the ultraviolet (Hill et al. 1992, Ap.J. 395, L37) and
in H alpha (Petit et al. 1988, A.Ap.Suppl. 74, 475) show no H II region
within about 10" (= 150 pc) of the supernova's position. The H alpha
result puts an upper limit on the luminosity of any H II region
in the area that would be exceeded by a main sequence O star.
The ultraviolet images also indicate that the extinction in the
direction of M81 is about 1.5 mag in the V band."
1993 April 1 (5739) Brian G. Marsden
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