Central Bureau for Astronomical Telegrams
IAUC 4948: 1987A; NSV 01098
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Circular No. 4948
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 or GREEN@CFA.BITNET MARSDEN or GREEN@CFAPS2.SPAN
SUPERNOVA 1987A IN THE LARGE MAGELLANIC CLOUD
A. Crotts, NASA Goddard Space Flight Center; and W. Kunkel,
Observatories of the Carnegie Institute of Washington, report: "The
innermost light echoes around SN 1987A (IAUC 4791, 4943) have evolved
significantly since March 1989 (cf. Crotts et al. 1989, Ap.J. 347,
L61). We obtained new continuum-band images with the Las Campanas
2.5-m telescope on 1989 Dec. 18 using a CCD with 0".16/pixel sampling.
In best seeing stellar images were about 0".7 FWHM. (We also have
intermediate-epoch data to aid in interpolating between March and
December.) The off-center 3"-diameter ring prominent last March has
shifted 0".5 northwestward and hence is evolving more like the echo
from an inclined cylinder than a flat sheet (for analyses, see Crotts
op. cit. and Chevalier 1990, Proc. Santa Cruz SN Workshop). The two
'horns' described by Crotts et al. have also changed: the protrusion
south of star 3 has elongated and shifted 0".5 westward, while the
other has condensed into a more pointlike structure 1".8 west and 0".8
south of the supernova. A new structure has appeared extending 3"
northeast from star 3. Most of the fainter echo extending to 9" from
the supernova last March has disappeared. The brighter glow to radius
6" is now less circular, like the crown of the 'Napoleonic hat'
described on IAUC 4943; the 'tips' of this structure consist primarily
of sources seen before SN 1987A." S. Heathcote, Cerro Tololo
Interamerican Observatory; and Crotts add: "Our spatially resolved,
high-dispersion spectra show, over the same period, significant changes
in the structure of the emission-line nebula around SN 1987A. In CTIO
4-m echelle spectra from Aug. and Dec. 1989, the structure of the
nebula in both forbidden and the Balmer lines showed details consistent
with those described by Wampler et al. on IAUC 4943. However, spectra
obtained in March 1989 with the same equipment show several compact
regions, emitting only in the Balmer lines, superposed on this
structure. These features were also visible in the H-alpha images of
Crotts et al. mentioned on IAUC 4791." Crotts stresses that most of
these structures have changed significantly in less than a year and,
consequently, they should be monitored frequently.
NSV 01098
Visual magnitudes by A. Pereira, Cabo da Roca, Portugal: 1989 Nov.
23.04 UT, 10.8; 28.18, 10.4; 30.19, 10.5; Dec. 22.84, 10.3; 24.04, 10.2.
1990 January 18 (4948) Brian G. Marsden
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