Electronic Telegram No. 5370
Central Bureau for Astronomical Telegrams
Mailing address:  Hoffman Lab 209; Harvard University;
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Prepared using the Tamkin Foundation Computer Network


(10424) GAILLARD
     J.-F. Gout, Starkville, MS, USA, reports the discovery of the binary
nature of the minor planet (10424) from the occultation of the magnitude-13.0
star UCAC4 558-046959 on 2024 Jan. 14.252 UT.  The minor planet was at mag
18.0, which was five magnitudes fainter than the occulted star.  Two
occultations of 0.45 and 0.26 s (chord lengths 4.3 and 2.6 km) were observed,
separated by an interval of 0.31 s (3.0 km).  For both occultations, the light
level of the occulted star dropped below the limiting magnitude (about 15.5).
The magnitude drops of at least 2.5 for both occultations excludes the
possibility of the occulted star being a close binary star.  Following the
occultation, dense light curves were obtained over a period of 16 days by M.
Conjat (Observatoire de la Cote d'Azur) and Gout.  In confirming the binary
nature of this minor planet, P. Pravec (Ondrejov Observatory, Astronomical
Institute of the Academy of Sciences of the Czech Republic) assessed the
light curves and concluded that the system is a fully synchronous binary with
a period of 42.18 +/- 0.02 hr, with a lower limit of 0.68 in the secondary-to-
primary diameter ratio -- consistent with the ratio of the occultation chord
lengths of 0.63.  For the ellipticity of the bodies, Pravec noted that the
observed rotational light-curve amplitude outside the mutual events suggests
that the equatorial axis ratio a/b = 1.25 (assuming that both bodies have the
same equatorial elongation).  D. Gault and D. Herald helped with the analysis
of the data and the preparation of this text.


NOTE: These 'Central Bureau Electronic Telegrams' are sometimes
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                         (C) Copyright 2024 CBAT
2024 March 15                    (CBET 5370)              Daniel W. E. Green