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IAUC 4521: 1987A; Poss. SN IN UGC 4060; 1987g1

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                                                  Circular No. 4521
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

      M. Karovska, L. Koechlin, P. Nisenson, C. Papaliolios and C.
Standley, Center for Astrophysics, report: "New measurements have
been made of the angular diameter of SN 1987A using speckle
interferometric techniques.  The data were recorded on Nov. 17-18 using
the 4-m telescope at Cerro Tololo Interamerican Observatory and
our PAPA camera speckle system.  Data were recorded in 10-nm passbands
at 533, 640, 656.5, 658.5 and 700 nm.  Data were also recorded
at 850 nm with a 250-nm passband.  Count rates were adjusted
using neutral-density filters to a level of 50 000 to 70 000
detected photons per second.  The supernova had a visual magnitude
of about 5.5 at that time.  The result of least-squares fitting of Airy
disks to the integrated power spectra gives the following diameters:
533 nm, 0".021; 640 nm, 0".020; 656.5 nm, 0".023; 700 nm, 0".024;
850 nm, 0".023.  All results have an error of 0".002.  Our
measurements made on a G8 star, BS 1008, whose diameter has been
estimated from the blackbody calculation to be 0".019, give a diameter
of 0".019 +/- 0".002.  We have also applied the same technique to
comparison stars recorded with the supernova data, and all results
show these stars to be unresolved, as expected.  The result at
656.5 nm, when combined with earlier data sets, appears to fit a
linear expansion velocity of 4000 km/s at 50 kpc, which may well
be a direct measure of the photospheric expansion.  The measured
diameter is substantially larger than the value that would be
obtained using a blackbody fit to the spectrum, but such a calculation
is only applicable to stars without extended atmospheres."
     Visual magnitude estimates by A. C. Beresford, Adelaide, South
Australia: Dec. 24.46 UT, 6.2; 25.48, 6.3; 27.50, 6.4; 28.49, 6.4.

     C. Pollas, Caussols Observatory, reports his discovery of a
possible supernova with the CERGA Schmidt telescope.  The object
is located 30" due west of the nucleus of UGC 4060 (R.A. = 7h48m.7, Decl. =
+14 09', equinox 1950.0) and was at mpg = 17 on Dec. 20.1 UT.

     Total visual magnitude estimate by D. Levy, Mt. Bigelow, AZ
(1.5-m reflector): Dec. 16.19 UT, 16.0:.

1987 December 28               (4521)              Brian G. Marsden

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