Central Bureau for Astronomical Telegrams
IAUC 4117: 4U 1820-30; 1982i; Occn BY PLUTO ON 1985 Aug. 19
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Read IAUC 4118
Circular No. 4117
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
4U 1820-30
L. Stella and N. E. White, EXOSAT Observatory and European
Space Agency; and W. Priedhorsky, Los Alamos National Laboratory
and Max-Planck-Institut fur Extraterrestrische Physik, Garching,
telex: "A 7-hr EXOSAT medium-energy observation of 4U 1820-30 =
NGC 6624 on Sept. 23-24 has revealed the presence of quasiperiodic
oscillations (QPO). The source was in a high non-bursting state
with the flux ranging from 400 to 500 mCrab. The centroid frequency
varied erratically on a timescale of an hour from 15 to 30
Hz with no obvious correlation with the overall source intensity.
The rms strength was ~ 5 percent and the FWHM ~ 20 Hz, independent
of the centroid frequency. A power spectrum of the whole observation
tends to average the QPO into a broad excess at frequencies <
40 Hz. One month earlier, this source had been observed by EXOSAT
to be in a lower state (~ 150 mCrab), displaying type-I bursts
every 3.2 hr. This is the first time that bursts have been seen
since 1976. We urge observers with archival x-ray data to study
further the QPO phenomenon from this source."
PERIODIC COMET HALLEY (1982i)
R. Rudy, G. Rossano, R. Puetter and R. Russell, Aerospace
Corporation, report the following magnitudes obtained with the
University of California at San Diego/University of Minnesota
1.52-m telescope on Mt. Lemmon on Oct. 2.5 UT, using a 12" aperture:
J = 12.4, [1.05 micron] = 12.8. A low-resolution (Delta-lambda/lambda
= 2 percent) spectrum over 0.84-1.38 microns was also obtained.
A. Tokunaga, University of Hawaii, reports the following
infrared observations of P/Halley made on Sept. 26 by C. Kaminski
and W. Golisch at the NASA Infrared Telescope Facility (using a
7"3 aperture): J = 13.1, H = 12.6, K = 12.4, L = 12.5 +/- 0.1, [8.7
microns] = 5.7 +/- 0.2, N = 4.7 +/- 0.2, Q = 1.8 +/- 0.2. The color
temperature on this date was ~ 210 K at 8.7-20.0 microns.
OCCULTATION BY PLUTO ON 1985 AUGUST 19
With reference to the item on IAUC 4097, several contributors,
including observer N. Brosch himself, have remarked that the
observed event would have involved Pluto itself, not 1978 P1.
1985 October 7 (4117) Brian G. Marsden
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