Central Bureau for Astronomical Telegrams
IAUC 4333: 1987A
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Circular No. 4333
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
SUPERNOVA 1987A IN THE LARGE MAGELLANIC CLOUD
G. Sonneborn, IUE Observatory, Goddard Space Flight Center;
and R. Kirshner, Center for Astrophysics, report: "IUE spectra
taken on Feb. 27, 28, Mar. 1 and 2 confirm the detection of Sanduleak
-69 202 beneath the fading far-ultraviolet flux of SN 1987A
reported by the European IUE SN Team (IAUC 4327, 4330). The
identification of the detected spectrum with Sanduleak -69 202 is based
on the presence and relative strengths of C III 117.5, Si II 126.0,
Si III 130.0, C II 133.5 nm and Fe III features between 185 and
200 nm. The best spectral match to Sanduleak -69 202 in the IUE
archives is the B3 Ia star Sanduleak -70 50. (We acknowledge the
assistance of E. Fitzpatrick, Joint Institute for Laboratory
Astrophysics, with the spectral classification.) The continuum flux
level (about 7.0 x 10*-14 erg cm-2 s-1 A-1 between 125.0 and 137.5 nm)
is within a factor of two of that expected for a B3 supergiant in
the LMC with the known optical properties (B3 Ia, V=12.3, E(B-V) <
0.17) of Sanduleak -69 202. However, the far-ultraviolet spectrum
below 150 nm is too steep for a B3 supergiant. Analysis of the
spatially-resolved ultraviolet spectra also shows that the spectrum
shortward of 150 nm is too wide for a single point source.
The far-ultraviolet brightness distribution perpendicular to the
dispersion is consistent with two point sources separated by about
3", with the dimmer star to the north of Sanduleak -69 202. The
position angle of the IUE large-aperture (10" x 20") major axis for
these observations is 330 deg. The second star is presumably star 2
of West (IAUC 4319), which he suggested was bluer than a B3 star.
This star also shows strong absorption at Si II, Si III and C II.
Apparently neither star 1 nor star 2 has exploded. The ultraviolet
spectrum of the supernova has continued to fade and in the
115-200 nm region is detectable only as a broad emission feature
(about 5000 km/s FWHM) centered near 190 nm. The width of the
spectrum longward of 180 nm is consistent with a single point source,
and its appearance bears a strong resemblance to the ultraviolet
spectra of both SN Ia and SN Ib. The following V estimates (not
corrected for any B-V dependence) have been derived from IUE fine-
error-sensor measurements: Feb. 26.83, 4.45; 27.45, 4.43; 27.64,
4.40; 27.90, 4.45; 28.07, 4.46; 28.50, 4.46; 28.82, 4.50; Mar.
1.04, 4.52; 1.46, 4.51; 1.66, 4.55; 2.02, 4.56; 2.81, 4.48;
3.07, 4.54; 3.81, 4.55; 3.96, 4.54; 4.13, 4.54; 4.47, 4.56;
4.68, 4.58; 4.87, 4.54; 5.45, 4.57. The calibration was checked
against HR 2015, for which we measured V = 4.37 on Feb. 26.9."
1987 March 7 (4333) Brian G. Marsden
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