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IAUC 8746: 2000 QL_251; BF Cyg

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IAUC number

                                                  Circular No. 8746
Central Bureau for Astronomical Telegrams
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
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2000 QL_251
     K. S. Noll, Space Telescope Science Institute; D. C. Stephens,
Johns Hopkins University; W. M. Grundy, Lowell Observatory; and H.
F. Levison, Southwest Research Institute, report the detection of a
binary companion to the transneptunian object 2000 QL_251 (cf. MPEC
2001-M34, 2001-S09; MPO 77471; orbital elements a = 47.65 AU, e =
0.216, i = 3.68 deg, epoch 2006 Sept. 22.0 TT); orbit integrations
carried out by the Deep Ecliptic Survey group show this object to
be in 1:2 resonance with Neptune.  It is the first binary to be
found in this dynamical group, sometimes referred to as "twotinos".
The observations were made during 2006 July 25.433-25.459 UT with
the High Resolution Camera of the Advanced Camera for Surveys on
the Hubble Space Telescope (HST), using the clear filters with one
300-s exposure at each of four dithered positions on the detector.
The two components are clearly resolved in each image and in the
coadded image.  The two components are separated by an angular
distance of 0".261 +/- 0".001.  The two components are
indistinguishable in magnitude within measurement uncertainties.
One of the two equal brightness components lies at a position angle
of 247.6 +/- 0.4 deg as measured from the other component.  The
projected separation of the objects in the sky plane is 7250 +/- 30
km.  The HST corrected for parallax and tracked both components of
2000 QL_251 as they moved together at an average rate of 0".022/min.

     M. L. Sitko, University of Cincinnati and Space Science
Institute; and D. K. Lynch, R. W. Russell, and C. C. Venturini,
Aerospace Corporation, report on 0.8- to 5.5-micron spectroscopy of
BF Cyg on Aug. 22.37 UT using SpeX at the Infrared Telescope
Facility.  The star appears to show a low-excitation shell.  Many
weak emission lines are present against what appears to be a normal
stellar continuum.  The H I Paschen lines are very weak in emission,
and the Brackett and Pfund lines were undetected except for weak
Br_gamma.  He I 1.0830-microns showed a P-Cyg profile, but He I
2.0581-microns was not detected.  Weak absorption of the first
overtone of CO at 2.3 microns was seen, and the Ca II infrared
triplet was present in emission.  A strong emission line appears
near 3.3145 microns.  The lines were not resolved spectrally and
thus are very narrow.

                      (C) Copyright 2006 CBAT
2006 September 12              (8746)            Daniel W. E. Green

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