Electronic Telegram No. 5714
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


(59195) 1999_BG2
     S. Kidd, British Astronomical Association, reports the discovery of an 
apparent satellite of the minor planet (59195), based on an occultation of the 
star UCAC4 517-112620 (which has Gaia catalogued magnitudes G = 13.66 and R = 
12.86) on 2026 June 18.012 UT.  This main-belt asteroid had a magnitude of 
19.9, which was 6.2 magnitudes fainter than the target star.  The observation 
was made near Stevenage, Hertfordshire, UK, using a 35-cm telescope (+ ASI432 
CMOS camera and a GPS-triggered flasher).  The recording, with a limiting 
magnitude of approximately G = 15.4, showed two consecutive occultations 
lasting 0.62 and 0.17 s, respectively, with a separation of 0.97 s.  This 
corresponds to chord lengths of 6.2 and 1.7 km, and a distance of 9.7 km 
between the chords at the minor planet.  The flux of each drop was lower than 
that of the comparison star, UCAC4 517-112565, which has Gaia magnitudes of 
15.07 (G) and 14.36 (R).  The depths of these drops rule out a double star as 
the cause of the light curve.  The sky-plane configuration diagram showing 
the observed occultation chord is posted at the following website URL: 
http://www.cbat.eps.harvard.edu/iau/cbet/005700/CBET5714_Fig1.png.  The 
separation of the two bodies was 0".0086 in p.a. 106 +/- 3.6 degrees with a 
sky-plane separation of 14.2 km.  
     Representative models of the system, as well as the observed and 
superimposed modeled light curves, are posted at the following website URL: 
http://www.cbat.eps.harvard.edu/iau/cbet/005700/CBET5714_Fig2.png.  Assuming 
that the main body is spherical with a diameter corresponding to the NEOWISE-
catalogued diameter of 6.3 +/- 0.4 km, Fresnel modeling of a central chord 
provides a good fit to the first drop in the light curve.  In the upper model, 
the minimum size of the apparent satellite is modeled as an ellipse of 1 x 2 
km.  The lower model shows the apparent satellite's maximum size (assuming 
that it is circular) with a diameter of 2.5 km.
     D. Herald (who forwarded this report to the Central Bureau) and D. Gault, 
Trans-Tasman Occultation Alliance; and C. Weber, European Section, 
International Occultation Timing Association, all aided in the analysis.  The 
reader is also referred to the end notes on CBET 5679.


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      superseded by text appearing later in the printed IAU Circulars.

                         (C) Copyright 2026 CBAT
2026 July 9                      (CBET 5714)              Daniel W. E. Green