Electronic Telegram No. 5388
Central Bureau for Astronomical Telegrams
Mailing address:  Hoffman Lab 209; Harvard University;
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Prepared using the Tamkin Foundation Computer Network


(100624) 1997 TR_28
     Y. Ikari, Japan Occultation Information Network, submitted the following
item (revised by D. Herald):
     J. Kubanek, Strasice, Czech Republic;, and M. Ishida and Y. Ikari,
Moriyama, Shiga, Japan, report the discovery of the likely binary nature of
the Trojan minor planet (100624) from the occultation of the 11.6-magnitude
star Tyc2 1335-00979-1 on 2024 Jan. 23.74 UT.  The components were separated
by 25 km, with the smaller component having a diameter of 4 km.  The minor
planet itself was at mag 19.5 (eight magnitudes fainter than the occulted
star).  Diameters for this minor planet were not available via NEOWISE,
Akari Acua, or IRAS measurements; it's expected diameter, derived from its
absolute magnitude of 12.74 and an assumed albedo for a Trojan minor planet
of 0.057, is 16 km.  The light dropped below the limiting magnitude of the
recordings of all observers.  The limiting magnitudes were assessed as 13.0
(Kubanek) for one component, and magnitudes 13.4 (Ikari) and 12.3 (Ishida)
for the second component (that is, magnitude drops of greater than 1.0 were
observed for both components, excluding the possibility of the occulted star
being a close binary star).  Kubanek observed an occultation by the main
component of the system, with a chord length of 10.9 km, which establishes a
minimum diameter for the main component; compared to the chords of Ishida and
Ikari, his chord was displaced in the direction of its geocentric motion by
approximately 22 km.  Ishida and Ikari observed occultations by the second
component of the system, with chord lengths of 3.2 and 2.3 km; their chords
were closely aligned in the direction of apparent geocentric motion and were
separated by 3.5 km -- establishing the diameter of the second component as
4 km.  The close alignment of the two chords for the second component,
combined with the extent of the displacement of the chord for the main
component -- in both the directions of apparent geocentric motion and that
perpendicular -- excludes the possibility of the minor planet being a single
highly elongated body.  The sky-plane separation of the components was 8.9
mas in p.a. 64 deg, a distance of 25 km.  The albedo used for estimating the
diameter of a Trojan minor planet from its absolute magnitude came from a
referee.  D. Herald (Murrumbateman, Australia) helped with the analysis of
the data and the preparation of this text.


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                         (C) Copyright 2024 CBAT
2024 April 29                    (CBET 5388)              Daniel W. E. Green