Electronic Telegram No. 5571
Central Bureau for Astronomical Telegrams
Mailing address:  Hoffman Lab 209; Harvard University;
 20 Oxford St.; Cambridge, MA  02138; U.S.A.
e-mail:  cbatiau@eps.harvard.edu (alternate cbat@iau.org)
URL http://www.cbat.eps.harvard.edu/index.html
Prepared using the Tamkin Foundation Computer Network


(109013) 2001 QS_4
     P. Nosworthy, Trans-Tasman Occultation Alliance (TTOA), reports the
discovery of an apparent satellite of minor planet (109013) based on the
occultation of the star UCAC4 253-082876 (which has catalogued Gaia magnitudes
G = 13.2 and R = 12.6) on 2025 June 1.4993 UT.  The observation was carried
out from the Blue Mountains, west of Sydney, Australia, using a 28-cm
telescope (+ Watec WAT-910BD video camera).  Nosworthy observed two
consecutive occultations of 0.40 and 0.44 s, corresponding to chord lengths of
4.1 and 4.5 km.  The main-belt asteroid was 5 magnitudes fainter than the
star.  The light curve from the observation is posted at the following website
URL:  http://www.cbat.eps.harvard.edu/iau/cbet/005500/CBET5571_Fig1.png.  The
flux during both occultations dropped below the level of comparison star UCAC
253-082814 (magnitudes G = 14.2, R = 13.5), to the limiting magnitude of the
recording (approximately G = 14.9, R = 14.2), thereby excluding the
possibility that a single body occulted a double-star.  The NEOWISE-catalogue
diameter of the minor planet is 6.3 +/- 0.6 km.  Assuming that the chords
represent central occultations by both components, proportioning the NEOWISE
diameter on the basis of the relative chord lengths leads to component
diameters of 4.8 +/- 0.3 and 4.0 +/- 0.3 km.  These diameters are used in the
sky-plane configuration diagram showing the observed occultation chords posted
at URL http://www.cbat.eps.harvard.edu/iau/cbet/005500/CBET5571_Fig2.png.  The
component diameters closely match and are consistent with the observed chord
lengths, and the overall configuration excludes a single body causing both
occultation events.  The separation of the satellite is 0".0139 in p.a. 298
degrees, with a sky-plane separation of 14.8 km.  D. Herald and D. Gault
(both members of TTOA) aided in the analysis.


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      superseded by text appearing later in the printed IAU Circulars.

                         (C) Copyright 2025 CBAT
2025 June 17                     (CBET 5571)              Daniel W. E. Green