Electronic Telegram No. 5742 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 (1757) PORVOO B. Lade, A. Wendelborn, and P. Martinaitis, Astronomical Society of South Australia, report the discovery of an apparent satellite of minor planet (1757) based on an occultation of the star UCAC4 312-094580 (which has catalogued Gaia magnitudes G = 11.4 and R = 10.3) on 2026 July 7.487 UT. This main-belt asteroid had a magnitude of 16.6, which is 5.2 magnitudes fainter than the target star. Lade observed from Mawson Lakes, South Australia, using a 20-cm telescope (+ ZWO 533MM Pro camera) and recorded two consecutive occultations of duration 0.30 and 2.73 s with an interval between the occultations of 3.30 s, corresponding to chord lengths of 1.71 and 15.54 km, respectively, with the distance between the chords being 18.83 km. Wendelborn observed from Largs North, S.A., using a 11.4-cm Unistellar eVscope (+ IMX224 sensor) and recorded a single occultation of duration 1.20 s, corresponding to a chord length of 6.83 km. Martinaitis observed from Salisbury, S.A., using a 20-cm telescope (+ ZWO 462MM camera) and recorded a single occultation of duration 1.85 s, corresponding to a chord length of 10.53 km. The flux of the two drops in Lade's recording fell below the level of the catalogued Gaia magnitudes of 12.5 (G) and 11.6 (R) of the comparison star UCAC4 313-096918 and close to the limiting V magnitude of the recording (which was approximately 14.2). The flux for Wendelborn's and Martinaitis's observations fell close to the limiting V magnitudes of the recordings, which were approximately 13.4 and 14.7, respectively. If the star was a double star, either Wendelborn or Martinaitis would have necessarily observed a second occultation consistent with that of Lade, and the absence of that second occultation excludes a double star from being the explanation for Lade's light curves. The three chords across the main body are fitted by an ellipse of 15.9 x 10.8 km. This has a mean diameter of 13.1 km, which is within the weighted mean from NEOWISE and Akari AcuA measurements of 13.0 +/- 1.0 km, with the 14.5-km single-occultation chord recorded at an occultation by this asteroid on 2024 Dec. 30 being consistent with the fitted ellipse. Fresnel modeling of the light curve suggests that the minimum size of the apparent satellite is an ellipse of size about 1.5 x 0.8 km, with the maximum size of a circular body being about 2.6 km. The apparent satellite is at a separation of 0".00285 in p.a. 274 +/- 2 degrees, with a sky-plane separation of 27.5 km. The sky-plane plot of the system can be found at the following website URL: http://www.cbat.eps.harvard.edu/iau/cbet/005700/CBET5742_Fig1.png. The observed light curves, as well as those derived from Fresnel modeling, can be found at http://www.cbat.eps.harvard.edu/iau/cbet/005700/CBET5742_Fig2.png. D. Herald and D. Gault, Trans-Tasman Occultation Alliance; and C. Weber, European Section of the IOTA, aided in the analysis, while B. Anderson (IOTA) provided the Fresnel diffraction software. 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 September 22 (CBET 5742) Daniel W. E. Green