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IAUC 4567: 1987A; 1988a

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                                                  Circular No. 4567
Central Bureau for Astronomical Telegrams
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
TWX 710-320-6842 ASTROGRAM CAM    Telephone 617-495-7244/7440/7444

     S. Heathcote and N. Suntzeff, Cerro Tololo Interamerican
Observatory, telex:  "N. Caldwell has obtained direct BVR CCD frames
with the CTIO 1.5-m telescope of the region around SN 1987A on Mar.
19, confirming the two arc-shaped nebulae (cf. IAUC 4561, 4564).
The mean colors of both the inner and outer rings are B-V = +1.2,
V-R = +0.1; there are no obvious color variations within each ring.
The surface brightness of the ring is V about 21.5 mag/arcsec2 in the
brighter knots.   The radii are 33".0 and 54".0 (+/- 0".5) from the SN,
the thicknesses being typically 5"-10".  At p.a. 60 deg, there is a
short arc with a radius of 52".0.  J. Huchra and R. Olowin have
obtained low-dispersion spectra (range 375-525 nm, resolution 0.6 nm;
slit width = 1".4 and slit position angle = 233.3 deg, tangential to the
ring; CTIO 4-m telescope) on Mar. 19 of the brightest knots in the
outer arc, 25" east and 50" north of SN 1987A.  The spectrum is
clearly that of the SN, which confirms that the arc-shaped nebula
is a light echo.  The spectrum is quite different from that of SN
1987A itself, obtained on the same night with the same equipment.
We have averaged our spectral data archive (which contains almost
nightly spectra of SN 1987A) month by month, and find that the
spectrum is consistent with the average spectra in 1987 Apr. and
inconsistent with all other months, including 1987 May when the SN
was at maximum.  A spectrum of the inner ring was obtained, by the
same observers with the same equipment on Mar. 20 (slit positioned
on a bright knot 25" east and 22" north of the SN and slit position
angle 126.3 deg), that is more nearly consistent with the average of
the spectra of SN 1987A obtained during 1987 May.  Since the
spectrograph slit is much more narrow than the thickness of the ring,
we cannot exclude the possibility that parts of each ring reflect
the light emitted by SN 1987A at different epochs.  On comparing a
1988 Jan. 27 CCD frame (obtained by B. Weller with the CTIO 1.5-m
telescope) with the present images, we find that the inner arc has
expanded by 3".0 +/- 0".5, or 1".8/month.  Noticeable changes in the
arc structure occurred between these dates.  The outer arc is not
visible in the earlier frames due to strong SN ghost images."

     Total visual magnitude estimates:  Mar. 6.01 UT, 8.1 (J. E.
Bortle, Stormville, NY, 0.32-m reflector); 12.01, 7.4 (Bortle);
18.77, 6.7 (S. Baroni, Milan, Italy, 20x80 binoculars).

1988 March 21                  (4567)            Daniel W. E. Green

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