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IAUC 4640: 3C 446; PSR 1957+20; N Oph 1988

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                                                  Circular No. 4640
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

3C 446
     E. Perez, Instituto de Astrofisica de Canarias, reports: "The
optically violent variable quasar 3C 446 was observed
spectrophotometrically on Aug. 11 and found to be in outburst.  While
the object has been for the past four years (at least until June) in a
low state, fainter than about mag 18, we calculate from the raw
unreduced spectrum that it is now at mag 15.5.  Intensive photometric
and spectroscopic monitoring at all wavelengths (x-ray, ultraviolet,
optical and infrared) would be of utmost importance in following up
this outburst.  The C IV and C III] emission lines are very weak, and
the Mg II absorption system at z = 0.86 is clearly visible against the
bright continuum."

PSR 1957+20
     S. Djorgovski and C. R. Evans, California Institute of
Technology, report: "We obtained a detailed lightcurve of the proposed
optical counterpart (cf. IAUC 4617) to the eclipsing millisecond
pulsar 1957+20.  The light variation matches the 9.17-hr orbital
period of the pulsar, with Gunn r = 19.36 at maximum, g-r = +0.66 and
variation amplitude 0.85 mag.  The centroid of the optical counterpart
displays a 9.17-hr periodic wobble with amplitude 0".5, indicating the
presence of a field star separated by 0".8-1".0.  If the minimum light
is due entirely to the field star, the pulsar companion would have
peak r = 20.05 and g-r = +0.45, not including extinction.  If the
visual extinction is 1 mag, the effective temperature of the
counterpart is 5800 K.  Assuming the distance 0.9 kpc and 1 mag visual
extinction, we derive for the pulsar companion Mv = 10.5 and radius
0.16 Rsun, close to that of a degenerate hydrogen dwarf."

     Visual magnitude estimates: June 14.42 UT, 10.6 (D. A. J.
Seargent, The Entrance, N.S.W.); 16.45, 11.3 (R. H. McNaught,
Coonabarabran, N.S.W.); 18.5, 11.2 (R. Keen, The Entrance, N.S.W.);
20.39, 11.2 (Seargent); 22.44, 11.5 (McNaught); 24.41, 11.6
(McNaught); 26.42, 10.6 (P. Williams, Heathcote, N.S.W.); 30.2, 10.6
(R. E. Royer, Wrightwood, CA); 30.71, 11.5 (McNaught); July 5.94, 11.3
(Schmeer); 7.3, 11.1 (Royer); 9.93, 11.1 (P. Schmeer, Bischmisheim,
West Germany); 12.50, 11.7 (Williams); 15.50, 11.6 (Williams); 18.35,
11.7 (Seargent); 20.45, 11.6 (Seargent).

1988 August 13                 (4640)              Brian G. Marsden

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