Electronic Telegram No. 4394
Central Bureau for Astronomical Telegrams
Mailing address:  Hoffman Lab 209; Harvard University;
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Prepared using the Tamkin Foundation Computer Network


(190166) 2005 UP156
     B. D. Warner, Palmer Divide Station, Center for Solar System Studies,
Landers, CA, USA; and A. W. Harris, "MoreData!", La Canada, CA, USA, report
that CCD photometric observations made between May 4 and 23 with a 0.30-m
Schmidt-Cassegrain reflector show that minor planet (190166) 2005 UP156 is a
fully-synchronous binary system with an orbital/rotational period of 40.542
+/- 0.008 hr.  The V magnitude was 16.0 on May 4, brightening to 15.2 on May
23.  The out-of-eclipse lightcurve shows an amplitude of about 0.5 magnitude
with eclipse attenuations of about 0.6 mag.  The deeper event lasts about 2.8
hours.  The effective secondary-to-primary diameter ratio is estimated to be
0.8 +/- 0.1.  The out-of-eclipse amplitude suggests that both bodies are quite
elongated, so the size ratio should be regarded with some caution.  The phase
angle on May 4 was 10.9 degrees; it decreased to 10 deg on May 10 and then
increased to 14.8 deg on May 23.  The phase-angle-bisector longitude (L_pab)
went from 230 to 239 deg, while the latitude, B_pab, went from 5.8 to 10.1
deg.  Observations by Warner during 2014 Aug. 9-23 (at phase angle range
47.7-38.9 deg, L_pab range 2-8 deg, and B_pab range 5-3 deg) showed a
large-amplitude lightcurve of 0.79 mag and period 40.5 hr.  There were no
indications of the binary nature seen at that time (Warner 2015, Minor Planet
Bull. 42, 41-53).  However, that data set was considerably sparse compared to
the current one, which makes comparisons of results between the two somewhat
suspect.
     Observations are continuing.  Radar observations at Arecibo are planned
for early June into August.  Those data should allow a more exact
determination of the system parameters.  The phase angle through early July
will increase to 36 degrees, while L_pab will go from the current 239 deg to
279 deg, and B_pab will progress from 10 to 21 degrees.  It's very possible
that the changing viewing geometry will cause the eclipse events to become
either better defined or even disappear, and so it will be important to have
optical as well as radar observations during the coming weeks in order to
provide the data needed to define the system parameters with assurance.


NOTE: These 'Central Bureau Electronic Telegrams' are sometimes
      superseded by text appearing later in the printed IAU Circulars.

                         (C) Copyright 2017 CBAT
2017 May 24                      (CBET 4394)              Daniel W. E. Green