Electronic Telegram No. 5552
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


(31736) 1999 JR_73
     C. Weber (Berlin, Germany), on behalf of the European Section of the
International Occultation Timing Association (IOTA), writes that D. Smith,
observing from two sites near Granada, Spain, reports the discovery of an
apparent satellite of the minor planet (31736) via the Stellar Occultation
Data Input System (SODIS).  The detection was achieved through occultation
observations of the 12.4-magnitude star UCAC4 401-061053 (Gaia DR3 star
number 6316990418098769408) on 2025 Apr. 22.055 UT.  The observation revealing
the satellite was carried out from Gergal (Spain) using a 20-cm Newtonian
telescope (+ ASI462MM camera).  The light curve (which is posted at URL
http://www.cbat.eps.harvard.edu/iau/cbet/005500/CBET5552_Fig1.png; see CBET
5521 for explanation of the graph) shows two consecutive drops of 0.37 and
0.13 s, with an interval of 0.808 s.  The resulting chord lengths are 5.8 km
for the first event (chord 3) and 1.51 km for the second (chord 2).  Both
drops reached a depth greater than the V magnitudes of two faint comparison
stars (UCAC4 401-061056, V = 14.0; UCAC4 401-061064, V = 14.7), which rules
out the hypothesis of a double star as the reason for the consecutive
occultation events.  The slightly smaller light drop of the second event is
consistent with Fresnel diffraction at a body with a diameter of 1.5 km.
The remote-controlled second observation from Gorafe (28-cm Schmidt-Cassegrain
telescope + ASI174MM Cool camera) shows one 0.23-s occultation event, which
corresponds to a chord length of 2.67 km (chord 1).  The light curve is
posted at http://www.cbat.eps.harvard.edu/iau/cbet/005500/CBET5552_Fig2.png.
The depth of the dip is fainter than V = 14.7 (comparison star UCAC4
401-061064), which again rules out a double-star explanation.  The position
of the apparent satellite relative to the main body is 0".0078 in p.a. 123
degrees.  The sky-plane plot conveys the light curves of both stations (see
URL http://www.cbat.eps.harvard.edu/iau/cbet/005500/CBET5552_Fig3.png).
Chord 2 depicts the apparent satellite, whose size was set to a circle with
a diameter matching the chord length of 1.51 km.  The size of the apparent
satellite is limited to a certain extent by chord 1, but it is not possible
to draw any conclusions.  The main body (chord 3) was fitted elliptically,
resulting in a profile of 5.98 x 2.55 km (p.a. 96.9 degrees for the long
axis).  This matches the NEOWISE catalogue diameter of 5.1 +/- 0.6 km and
clearly excludes the main body as the reason for the second light drop.  The
two main-body chords are the first-ever occultation chords for this minor
planet.  D. Herald of the Trans-Tasman Occultation Alliance (TTOA) and IOTA;
and D. Gault, TTOA performed independent data analysis to confirm the results.


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

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2025 May 1                       (CBET 5552)              Daniel W. E. Green