Central Bureau for Astronomical Telegrams
IAUC 4604: 1987A; T Leo
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Circular No. 4604
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
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
MARSDEN or GREEN@CFA.BITNET MARSDEN or GREEN@CFAPS2.SPAN
SUPERNOVA 1987A IN THE LARGE MAGELLANIC CLOUD
M. Karovska, L. Koechlin, P. Nisenson, C. Papaliolios and C.
Standley, Center for Astrophysics, report: "New measurements have been
made of SN 1987A, showing a substantial asymmetry in the expanding
shell. Speckle interferometric processing was applied to data that
were recorded using the CTIO 4-m telescope and our PAPA camera speckle
system during Feb. 29-Mar. 2 and Apr. 9-12. Data were recorded in
10-nm passbands at several wavelengths. We report on results obtained
at two wavelengths, 533 nm and 656 nm (H alpha). Previous diameter
measurements were reported on IAUC 4521 and 4457. For those data,
azimuthal averages of the power spectra were performed, and Airy disks
were fitted. These new data are of better quality than the earlier
data, mostly due to better seeing. The higher signal-to-noise and
increased size of the shell have allowed greater accuracy in the
measurements. A substantial asymmetry is observed in displays of the
power spectra and in the image reconstructions. The images are
elongated along an axis tilted about 20 degrees from north. The
image is 20 to 30 percent longer along this axis and is somewhat
brighter in the southwest direction. Similar asymmetries have been
detected in previous observations, but the poorer signal-to-noise in
those data and the smaller scale of the SN at the time precluded
accurate measurements of the effect. A summary of the results
follows. The azimuthally averaged diameter in Feb.-Mar. was 0".019 at
533 nm and 0".020 at 656 nm. In Apr. the diameter was 0".026 at 533
and 0".027 at 656 nm. The 1-sigma error bars in these measurements
are about 0".001. The Feb.-Mar. data give a 0".017 minor axis and
0".025 major axis (+/- 0".002). In April the minor axis was 0".025
and the major axis 0".030 (+/- 0".002). Data recorded on comparison
stars gave symmetric power spectra and images and were unresolved
(< 0".001 angular diameter). New measurements of Alpha Cen A give a
diameter of 0".010 +/- 0".001, and the images show no asymmetry.
Photometric estimates for Alpha Cen give a diameter of 0".009."
T LEONIS
Visual magnitude estimates: May 20.96 UT, [11.0 (P. Schmeer,
Bischmisheim, West Germany); 23.87, 10.1 (Schmeer); 24.89, 10.1
(A. Boattini, Florence, Italy); 25.89, 10.2 (Boattini); 27.06,
10.5 (G. Dyck, North Dartmouth, MA).
1988 May 27 (4604) Brian G. Marsden
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