Central Bureau for Astronomical Telegrams
IAUC 3984: PULSAR IN LMC; 1984g
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Circular No. 3984
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
PULSAR IN LARGE MAGELLANIC CLOUD
J. Middleditch, Los Alamos National Laboratory: and C.
Pennypacker, Lawrence Berkeley/Space Sciences Laboratories, University
of California, communicate: "Optical pulsations corresponding to
the x-ray pulsar in the LMC supernova remnant 0540-69.3 (IAUC 3928)
were detected in 2.3 hr of time-series data taken with the Cerro
Tololo Interamerican Observatory 4-m reflector on Aug. 27.35 UT in
the 320-750-nm band. The pulsations had a barycentric period of
50.28149 +/- 0.00001 ms, corresponding to an average slowdown of
41.53 ns/day since the 1979 observations. The pulse profile is
approximately a 23rd-magnitude sinusoid and corresponds to ~ 2 percent
of the nebular synchrotron light (Chanan, Helfand and Reynolds
1984, Ap.J.Lett., submitted) included in the (centered) 4"6
circular aperture. The amplitudes of the 40-, 60-, 80-, and 140-Hz
harmonics relative to the amplitude of the fundamental are,
approximately: 0.08, 0.13, 0.14, and 0.07 (uncertainties +/-0.05)."
COMET AUSTIN (1984g)
Z. Sekanina, Jet Propulsion Laboratory, reports that observations
by C. S. Morris of the anti-tail (below) indicate that the
elevated emission of dust began before perihelion: a minimum particle
radius of several tens of microns is suggested. The earth will
cross the comet's orbit on Sept. 13.9 UT, at which time the antitail
should be quite noticeable toward p.a. 115. The observational
uncertainty of 7 deg in the spike's p.a. in early Sept. translates
into the following predicted p.a. ranges: Sept. 27, 109-125;
Oct. 7, 99-120; Oct. 17, 80-103; Oct. 27, 54-80. Since
the earth's cometocentric latitude will begin to increase rapidly
after the crossing, it is doubtful that the anti-tail will still be
visible in Oct. other than perhaps photographically.
Further total visual magnitude estimates and tail lengths:
Sept. 2.49 UT, 6.5, 25' in p.a. 117 (0.25-m reflector), 2 deg in p.a.
304 (C. S. Morris, 20x80 binoculars, near Mt. Wilson, CA); 2.88,
6.5 (S. Fujikawa, Onohara, and Y. Sakurai, Mito, Japan); 3.50, 6.4,
20' in p.a. 110 (0.25-m refl.), 1 deg 20' in p.a. 303.5 (Morris, 20x80
binoculars); 4.50, 6.6, 25' in p.a. 115 (0.25-m refl.), 1 deg in p.a.
306 (Morris, 20x80 binoculars); 6.36, 6.5 (D. W. E. Green, Harvard
College Observatory, 20x80 binoculars); 7.36, 6.8 (Green); 8.38,
6.9 (Green); 9.36, 6.9 (Green).
1984 September 10 (3984) Daniel W. E. Green
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