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IAUC 6760: 1997dh; RX J0558.0+5353; SW UMa

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                                                 Circular No. 6760
Central Bureau for Astronomical Telegrams
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
URL http://cfa-www.harvard.edu/iau/cbat.html
Phone 617-495-7244/7440/7444 (for emergency use only)

     O. Perdereau and J. C. Hamilton, on behalf of the Experience
de Recherche d'Objets Sombres (EROS) collaboration, report the
discovery on Oct. 20 and 21 CCD images taken by members of the EROS
team of an apparent supernova (V about 19), using the Marly 1-m
telescope at the European Southern Observatory, La Silla.  SN
1997dh is located at R.A. = 23h45m17s.17, Decl. = -44o56'45".1
(equinox 2000.0), which is 4" southwest of the center of the host
galaxy.  Nothing was present at this position on an image (limiting
mag about 22) taken on 1996 Oct. 10.  A finding chart can be found
at http://www.lal.in2p3.fr/EROS/SNe/Charts/.

RX J0558.0+5353
     N. M. Shakhovskoj, Crimean Astrophysical Observatory, Nauchnij;
and S. V. Kolesnikov, Odessa Astronomical Observatory, write:
"Periodic variations in the circular polarization, with period P =
0.006301 +/- 0.000055 day (544.4 +/- 4.8 s) and semiamplitude of
1.80 +/- 0.16 percent, were detected in this object on Oct. 4 at
the Shajn 2.6-m telescope (+ one-channel polarimeter + fast-rotating
achromatic quarter-wave plate and a broad red filter spanning
0.500-0.750 nm).  Variations of the circular polarization are
sinusoidal with the changing of the polarity.  The photometric
variations of the same observing run show P = 0.003592 +/- 0.000012
day; however, the peaks of the periodogram are accompanied by
aliases, one of which corresponds to the double frequency (P =
0.003120 +/- 0.000012 day = 269.5 +/- 1.0 s) and amplitude 0.035
+/- 0.003 mag.  This period is very near the period of 272.785 s
detected by Ashoka et al. (1995, A.Ap. 297, L83) in white light,
and the period of 272.74 s found by Haberl et al. (1994, A.Ap. 291,
171) in x-rays.  Light maxima coincide with the extreme positive
and negative circular polarization.  Johnson magnitudes from Oct. 4
(1.25-m telescope):  U = 13.29, B = 13.98, V = 13.91, R = 13.49, I
= 13.31."

     J. A. Mattei, AAVSO, reports that this SU UMa-type dwarf nova
is in superoutburst, as indicated by the following visual
observations:  Oct. 18.51 UT, [14.6 (G. Hanson, Brookfield, WI);
19.17, [13.0 (P. Schmeer, Saarbrucken, Germany); 19.490, 11.1
(Hanson); 19.969, 10.4 (B. Granslo, Nordahl Griegs Vei, Norway);
20.353, 10.5 (Hanson); 22.168, 11.2 (Schmeer, Bischmisheim,
Germany).  The star reached peak mag 9.6 during its last outburst
on 1996 Apr. 13.

                      (C) Copyright 1997 CBAT
1997 October 24                (6760)            Daniel W. E. Green

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