Electronic Telegram No. 5654
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


(7563) 1988 BC
     G. Viscome, International Occultation Timing Association (IOTA), reports
the discovery of an apparent satellite of minor planet (7563) based on an
occultation of the star UCAC4 368-083154 (which has catalogued Gaia magnitudes
G = 13.4 and R = 12.4), as observed on 2024 Apr. 25.3355 UT.  The main-belt
asteroid was 3.8 magnitudes fainter than the star.  Viscome observed from Lake
Placid, NY, USA, using a 37-cm telescope (Astrid GPS disciplined CMOS video
system) and recorded two consecutive occultations of duration 2.48 and 0.25 s,
corresponding to chord lengths of 16.4 and 1.7 km, respectively, with the
interval between the chords being 3.49 s.  The light curve is posted at URL
http://www.cbat.eps.harvard.edu/iau/cbet/005600/CBET5654_Fig1.png.  The flux
during the first occultation dropped to the limiting magnitude of the
recording (approximately G = 15.5 and R = 15.0), and the flux for the second
occultation dropped below the level of comparison star UCAC4 368-083236
(catalogued Gaia magnitudes G = 14.5, R = 13.8) but did not reach the limiting
magnitude of the recording.  While the magnitude drops observed are different,
the magnitude drops considered together are too large to be explained by a
double star.  The Fresnel diffraction analysis of the second drop was
consistent with an occultation by a satellite having a diameter of between 1.5
and 2.5 km.  The chord locations for these two diameters, together with a
comparison of the corresponding Fresnel light curve with the observed light
curve, are posted at the following website URL:
http://www.cbat.eps.harvard.edu/iau/cbet/005600/CBET5654_Fig2.png.  The sky-
plane configuration diagram showing the observed occultation chords, with the
main body drawn using the NEOWISE-catalogue diameter of 15.8 +/- 1.6 km, is
posted at http://www.cbat.eps.harvard.edu/iau/cbet/005600/CBET5654_Fig3.png.
The separation of the satellite is 0".0237 in p.a. 77.4 +/- 2 degrees, with
a sky-plane separation of 32 km.  D. Herald and D. Gault of the Trans-Tasman
Occultation Alliance and C. Weber of the European Section of the IOTA
aided in the analysis; B. Anderson (IOTA) provided the Fresnel diffraction
software.


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      superseded by text appearing later in the printed IAU Circulars.

                         (C) Copyright 2026 CBAT
2026 January 13                  (CBET 5654)              Daniel W. E. Green