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THE ASTRONOMER Electronic Circular No 3164      2016 Apr 26 18.38UT
Ed:Guy M Hurst, 16,Westminster Close, Kempshott Rise,  Basingstoke,
Hants, RG22 4PP,England.Telephone/FAX(01256)471074Int:+441256471074
INTERNET: GUY@TAHQ.DEMON.CO.UK      Backup: gmh@wdcc1.bnsc.rl.ac.uk
WORLD WIDE WEB                         http://www.theastronomer.org
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MAKEMAKE SATELLITE: S/2015 (136472) 1

A. H. Parker, Southwest Research Institute; M. W. Buie, Southwest Research
Institute; W. M. Grundy, Lowell Observatory; K. S. Noll, NASA/GSFC; report
the discovery of a satellite of the dwarf planet (136472) Makemake.

"We collected deep imagery of Makemake with the Wide Field Camera 3 on the
Hubble Space Telescope (HST) in the broad F350LP filter over two epochs in
April 2015.  In all six 725-second exposures collected over two sequential
HST orbits starting 2015 April 27.574 UTC a faint companion is visible.  The
companion, provisionally designated S/2015 (136472) 1, is 7.80 +/- 0.04 mag
fainter than Makemake in F350LP.  During these observations, the companion's
motion is perfectly consistent with Makemake's, at an offset of 0".124 +/-
0".001 in R.A. and 0".558 +/- 0".001 in Declination (J2000). In a subsequent
epoch starting 2015 April 29.762 UTC, an identical image set did not reveal
any co-moving sources up to two magnitudes fainter than S/2015 (136472) 1.

Makemake's high ecliptic latitude and the companion's lack of any
parallactic motion offset from Makemake make the serendipitous appulse of an
unbound trans-Neptunian Object extremely unlikely.  We infer that S/2015
(136472) 1 is on a nearly edge-on orbit that placed it too deep within the
PSF of Makemake to be recovered in the second epoch.  Utilising location
constraints from the non-recovery in the second epoch and assuming a
circular orbit, we find that the satellite's likely semi-major axis is
larger than 21,000 km and its orbital period is longer than 12 days."

M.P.E.C. 2016-H46 issued 2016 April 26