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IAUC 4358: 1987C; 1987A

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                                                  Circular No. 4358
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

     A. M. Cherepashchuk, Sternberg Astronomical Institute, cables
the discovery by Petrosian and Oganian of a supernova 11" east and
18" south of the center of Markarian 90 (MCG +9-14-47; R.A. = 4h26.1,
Decl. = +52 52', equinox 1950.0).  On Mar. 21, mpg = 17.5.

     O. Benvenuto, A. Clocchiatti, C. Feinstein, B. Garcia, H.
Luna, M. Mendez, and N. Morrell, Observatorio Astronomico de La
Plata, telex:  "We have been observing SN 1987A since Feb. 28 with
a 0.8-m Cassegrain telescope, a rotating half-wavelength plate
polarimeter, and Johnson UBVRI filters, and have found the linear
polarization in B, V, R, and I filters to be decreasing, while that
with the U filter exhibits irregular behavior.  The following
measurements are all given as percentages, with errors given
parenthetically in units of 0.01:

 1987          U           B           V          R          I

 Feb. 28    0.89 (42)   1.10 (10)   0.93 (4)   0.93 (4)   0.76 (7)
 Mar. 15    2.30 (36)   0.56  (6)   0.61 (6)   0.60 (4)   0.55 (4)
      21    2.62 (47)
      22                0.50  (7)   0.52 (5)   0.54 (5)   0.38 (5)

The position angle has remained almost constant at 40 deg +/- 3 deg in all
of the filters during the observational period.  The observed
wavelength dependence of the polarization does not appear to be in
agreement with that expected from interstellar dust."
     W. Couch, K. Taylor, C. McCowage, J. Bailey, and M. Cropper,
Anglo-Australian Observatory, report:  "Spectropolarimetry of SN
1987A using a Pockels cell and CCD as detector on Mar. 7 reveals
that there is a dip in the linear polarization centered on the
wavelength of the trough of the 630-nm H-alpha absorption feature.  The
dip is more narrow than the absorption trough with a full-width of
8.5 nm.  The polarization is reduced from 0.80 to 0.62 percent at
the center of the dip.  Uncertainties are typically 0.03 percent in
each 0.6-nm bin.  There is also evidence for a decrease in the position
angle from 40 deg to 35 deg at the same wavelength.  The dips are
evident at two grating positions centered on the H-alpha emission peak
and absorption trough.  There is no change in the polarization at
the H-alpha emission peak."

1987 April 3                   (4358)            Daniel W. E. Green

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