Central Bureau for Astronomical Telegrams
IAUC 5532: GEMINGA; PLUTO
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Circular No. 5532
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
Telephone 617-495-7244/7440/7444 (for emergency use only)
TWX 710-320-6842 ASTROGRAM CAM EASYLINK 62794505
MARSDEN@CFA or GREEN@CFA (.SPAN, .BITNET or .HARVARD.EDU)
GEMINGA
J. H. Seiradakis, Max Planck Institute for Radioastronomy,
Bonn, reports: "The 100-m radio telescope at Effelsberg was used to
search for the periodic signals reported at x-rays and gamma-rays
from the strong gamma-ray source Geminga. Two sets of data centered
at 1.41 and 1.675 GHz, covering 79.66 and 84.64 min, respectively,
recorded with a resolution of 230 microsec, were integrated
synchronously with the reported period of the source after taking
into account period-derivative and barycentric corrections. A mean
rms of about 330 microJy was obtained at both frequencies. No
periodic signals were observed, indicating a 3-sigma upper limit of
about 1 mJy. The bandwidth used was 100 MHz. The observations
were therefore sensitive for dispersion measures (DM) up to 100 pc
cmE-3. This corresponds to a distance of more than 2 kpc. A larger
DM would have dispersed the signals by more than one-tenth of
the period. Such DMs have not yet been encountered towards the
galactic anticenter. Geminga is the first neutron star known to
emit copious hard gamma-rays but no radio waves. This result has
serious implications for the emission mechanism of neutron stars,
and/or for the geometry of the emitting region."
PLUTO
T. Owen, Institute for Astronomy, University of Hawaii; T.
Geballe, U.K. Infrared Telescope (UKIRT); C. de Bergh, Observatoire
de Paris; L. Young and J. Elliot, Massachusetts Institute of
Technology; and D. Cruikshank, Ames Research Center, NASA, communicate:
"Spectra of the 1.45- to 2.40-micron region (resolution about 300)
of the combined flux of Pluto and Charon were recorded on the
nights of May 27 and 28 UT with the CGS4 spectrometer on UKIRT at
Mauna Kea. In addition to strong methane ice absorptions clustered
in both the H and K windows, we found a weak methane ice feature at
1.48 microns. We also detected weak absorptions at 2.15 and 2.35
microns that cannot be attributed to methane. We identify these
latter two features as the 2.15-micron absorption of N2 ice and the
(2,0) band of CO ice, respectively (based on work of B. Schmitt, R.
H. Brown, and J. Green). Since Pluto is at least 5 times brighter
than Charon within the K band (Bosh et al. 1992, Icarus 95, 319),
we conclude that all of these features are due to Pluto. N2 has
the highest vapor pressure of these three gases, and would, therefore,
be the dominant gas in Pluto's atmosphere, followed by CO and
CH4 if these gases are in vapor pressure equilibrium."
1992 May 30 (5532) Daniel W. E. Green
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