Central Bureau for Astronomical Telegrams
IAUC 7056: 1987A
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Circular No. 7056
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
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SUPERNOVA 1987A IN THE LARGE MAGELLANIC CLOUD
W. Kunkel, Las Campanas Observatory (LCO); S. Lawrence and A.
Crotts, Columbia University; and P. Bouchet, S. Heathcote, and R.
Probst, Cerro Tololo Interamerican Observatory (CTIO), report
brightening of the 'hotspot' (IAUC 6665, 6710, 6761) on the inner
ring around SN 1987A: "Images obtained on Oct. 31 UT at the LCO
2.5-m telescope (+ H-alpha filter; 0".6 FWHM seeing) show a strong
concentration of light at p.a. 31 deg and radius 0".59 on the inner
edge of the ring. A comparison was made to images taken on 1997
July 10 using the HST's WFPC2 in the F656N band, which includes
H-alpha and [N II] at 654.8 nm. H-alpha and [N II] images from
Oct. 31 were combined in the same ratio as in F656N, and the point-
spread function of the WFPC2 image was matched to that from Oct.
31. Subtraction of these shows a compact spot that now totals 3.7
percent of the H-alpha ring brightness, up from 1 percent in 1997
Apr. 26 data from HST/STIS, while the ring appears to have faded by
about 15 percent in H-alpha. No other H-alpha spots are seen
elsewhere on the ring, nor any spots in other bands: [N II] at
658.3 nm, [O III] at 500.7 nm, or continuum at 612 nm. Near-
infrared images obtained on 1998 Oct. 6 (4-m CTIO Blanco telescope;
0".5 FWHM seeing) show that the hot spot has also brightened
considerably in the He I 1083.0-nm line, and the spot now has 27
percent of the total brightness of the ring at this wavelength,
compared to only 15 percent in images obtained with the same
equipment on 1997 Nov. 23. The brightness of the ring has remained
constant, or only slightly increased (< 5 percent), over this
period. Similar images obtained on 1998 Feb. 13 are consistent
with a roughly linear increase in the hot spot's brightness with
time. Comparison of the Oct. 1998 H-alpha and He I images
suggests that the hot spot is slightly more compact in He I and
that its photocenter is displaced about 0".1 eastward along the
ring.
"In addition, R. Blum and S. Heathcote (CTIO) report that low-
resolution (R about 550), near-infrared (840-2400 nm) spectra
obtained on 1998 Nov. 10 with the 4-m telescope show strong lines
of He I at 1083 nm and [Fe II] at 1257, 1278, and 1644 nm. Much
weaker lines due to [S III] 953.0-nm, [S II] 1035-nm, Paschen-gamma
1094-nm, and [Fe II] 1533-nm were also detected. The line at 1278
nm may include a contribution from Paschen-beta; however, the
weakness of Paschen-gamma suggests that the [Fe II] line dominates.
The spatial profile of the He I 1083-nm line is asymmetric and
incipiently double-peaked, with the brighter peak being to the
northeast (the slit was oriented in p.a. 30 deg), consistent with
the hot-spot-plus-ring structure seen in images. The other lines
are too faint to reliably extract spatial information."
(C) Copyright 1998 CBAT
1998 November 20 (7056) Daniel W. E. Green
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