Electronic Telegram No. 4275
Central Bureau for Astronomical Telegrams
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S/2015 (136472) 1
     A. H. Parker, Southwest Research Institute; M. W. Buie, Southwest
Research Institute; W. M. Grundy, Lowell Observatory; and K. S. Noll,
Goddard Space Flight Center, NASA, report the discovery of a satellite of the
dwarf planet (136472) Makemake via deep imagery of obtained 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-s exposures collected over
two sequential HST orbits starting at 2015 Apr. 27.574 UTC show that a faint
companion is visible.  The companion, provisionally designated S/2015 (136472)
1, is 7.80 +/- 0.04 magnitude fainter than the primary in the F350LP band.
During these observations, the companion's motion is perfectly consistent with
that of the primary, at an offset of 0".124 +//- 0".001 in R.A. and 0".558 +/-
0".001 in Decl. (equinox J2000.0).  In a subsequent epoch starting on 2015
Apr. 29.762, an identical image set did not reveal any co-moving sources up to
two magnitudes fainter than S/2015 (136472) 1.  The primary's high ecliptic
latitude and the companion's lack of any parallactic motion offset from
the primary make the serendipitous appulse of an unbound trans-Neptunian
object extremely unlikely.  It is inferred that S/2015 (136472) 1 is in a
nearly edge-on orbit that placed it too deep within the point-spread function
of the primary to be recovered in the second epoch.  Utilizing location
constraints from the non-recovery in the second epoch and assuming a circular
orbit, the authors find that the satellite's likely semi-major axis is larger
than 21000 km and its orbital period is longer than 12 days.


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                         (C) Copyright 2016 CBAT
2016 April 26                    (CBET 4275)              Daniel W. E. Green