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IAUC 4781: 1987A

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                                                  Circular No. 4781
Central Bureau for Astronomical Telegrams
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

     C. Burrows, Space Telescope Science Institute; and Astrophysics
Division, ESA Space Science Department, reports: "CCD coronagraphic
images taken with the 2.2-m telescope at the European Southern
Observatory on 1988 Sept. 8 contain 16 pointlike sources down to a
limit of 20 mag in a 20" x 30" region centered on the supernova.  All
these sources appear consistent photometrically and astrometrically
with sources present on the pre-explosion digitized plate No. 4858
referred to by Walborn et al. (1987, Ap.J. 321, L41).  After
subtraction of these sources, all the remaining structure in the field
is consistent with fainter background stars present in both residual
images.  This shows that there is no apparent light echo with an
annular morphology and a thickness of 1" to 3" in the angular range 5"
to 10" from the supernova to a limit of R = 22 mag per square arcsec,
and it appears inconsistent with a sheet or spherical shell of dust as
being the cause of the inner echo reported by Bond et al. (IAUC 4733)."

     M. Karovska, P. Nisenson, C. Standley and C. Bailyn, Center for
Astrophysics; and S. Heathcote, Cerro Tololo Interamerican
Observatory, communicate: "The position of maximum brightness of
SN 1987A determined from speckle (1988 Dec., IAUC 4749) and CCD
(1989 Mar., IAUC 4753) images obtained at the CTIO 4-m telescope shows
evidence for a displacement of 0".15 +/- 0".07 from the astrometric
position of star 1 as measured by Testor (1987, A.Ap. 190, L1) and
Heap et al. (1987, A.Ap. 185, L10) in the pre-explosion images of the
Sk -69 202 complex.  The possibility of extended structure around the
supernova may result in an additional systematic error in the position
of the supernova itself not included in the above error estimates.
Analysis of pre-supernova plates suggested that star 1 may be composed
of two stars (Testor; Heap et al.) separated in the north-south
direction and allows a possibility that one of the components survived
the explosion.  Assuming the supernova itself continued to decay at
the same rate as it did during the period from day 500 to
approximately day 600, the change in slope after day 600 can be
explained by the presence of the other star.  In this case the visible
lightcurve is well fit by including a star with V = 13.4, probably a
supergiant of a spectral type between late A and early G.  The
pre-explosion magnitude of the B supergiant that became SN 1987A would
then have been V = 12.8.  Extrapolation of this fit predicts that the
lightcurve will flatten out by mid-July."

1989 May 17                    (4781)              Brian G. Marsden

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