Central Bureau for Astronomical Telegrams
IAUC 4401: Millisec PULSAR IN M28; PLUTO
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Circular No. 4401
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
MILLISECOND PULSAR IN M28
J. Middleditch, Los Alamos National Laboratory; A. G. Lyne
and A. Brinklow, University of Manchester; D. C. Backer and T. R.
Clifton, University of California, Berkeley; and S. R. Kulkarni,
California Institute of Technology, telex: "Following the proposal
that a discrete radio source in the core of the globular cluster
M28 might be a millisecond pulsar (Hamilton et al. 1985, A.J. 80,
606), we have used the 76-m Mk Ia radiotelescope at Jodrell Bank
and a Cray-XMP supercomputer at Los Alamos in a periodicity and
dispersion search for such a pulsar. Outputs from 32 channels of
1 MHz bandwidth near 1400 MHz were recorded every 300 microseconds for 90
min on both 1986 Dec. 6 and 1987 Jan. 2. The same barycentric
periodicity was found in both data sets and has been confirmed in
more recent observations. The pulsar has a barycentric period of
3054.3144 +/- 0.0001 microseconds (epoch 1987 May 31.0), a mean flux density
of 1.1 +/- 0.3 mJy and a dispersion measure of 120 +/- 5 pc cm-3,
consistent with an estimated distance of about 5 kpc to the cluster. The
observed period derivative is less than 3 x 10**-17, so the object
is almost certainly not in a binary system."
PLUTO
S. Sawyer, E. Barker, A. Cochran and B. Cochran, University
of Texas, report that they obtained time-resolved spectra of the
Apr. 4 occultation of Charon by Pluto using the CCD spectrograph
on the McDonald 2.1-m telescope. The 2.5-nm resolution spectrum
of Charon in the 0.5-1.0 micron region showed no evidence of methane
absorption. The Charon spectrum was flat and featureless, whereas
the Pluto spectrum was red and accounted for all of the methane
absorption in the Pluto-Charon system. The geometric albedo of
Charon is 0.41 at 0.6 micron. Lower-quality spectra of the Mar. 3
occultation of Charon by Pluto are consistent with these results.
M.-c. Wu and P.-s. Chen, Yunnan Observatory, telex: "We
observed the transit of Charon across Pluto on Apr. 26 with the
Yunnan 1-m telescope (+ CCD). Preliminary results indicate an
infrared depth of 0.53 mag on Apr. 26.762 UT; the predicted depth
was 0.49 mag on Apr. 26.764 (Tedesco and Dunbar 1986, Bull. AAS
18, 821). Outside of eclipse, the brightness of the system was
found to be I = 12.6, V = 13.7."
1987 June 3 (4401) Brian G. Marsden
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