Electronic Telegram No. 5685
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


(1045) MICHELA
     C. McPartlin, International Occultation Timing Association (IOTA), 
reports the discovery of an apparent satellite of minor planet (1045) based on 
an occultation on 2025 Oct. 9.169 UT of the star UCAC4 391-132283 (which has 
catalogued Gaia magnitudes G = 12.95 and R = 12.50).  The magnitude of (1045)
was 16.8 (or four magnitudes fainter than the target star).  The star is 
listed in Gaia DR3 as a non-single-star having a non-linear proper motion that
is compatible with an acceleration model with seven parameters.  McPartlin 
observed from Goleta, CA, USA, using a 13-cm telescope (+ Astrid GPS-
disciplined CMOS video system); the recording showed two consecutive 
occultations of durations 0.50 and 2.5 s, separated by 9.8 s, corresponding to 
chord lengths of 1.1 and 5.7 km.  The flux during for the first occultation 
dropped to that of comparison star UCAC4 391-132282 (Gaia magnitudes G = 14.0,
R = 13.5), and the flux for the second event dropped to the limiting magnitude 
of the recording (approximately G = 14.5 and R = 13.8).  The depths of these 
drops (1.0 and 1.5 in G, 1.0 and 1.3 in R) are sufficiently great to exclude 
the companion inferred from the Gaia non-single-star entry from being the 
explanation for the light curve.  The NEOWISE diameter of the minor planet is 
6.1 +/- 0.6 km.  The depth of the light curve for the main body indicates that
the observed chord was never far from the limb of the minor planet, and the 
body matching both the light curve and the NEOWISE diameter is an ellipse with 
axes of size 10.0 x 3.7 km.  The oblateness of this ellipse is consistent with 
the poorly determined oblateness given in Carry et al. (2024, A.Ap. 687, A38). 
Assuming that the apparent satellite is spherical, its diameter to be
consistent with the light curve is at least 2.2 km.  The separation of the 
apparent satellite was 0".0233 in p.a. 251 +/- 5 degrees, with a separation of 
25.0 km.  
     The observed light curve, together with the modeled light curve, is 
posted at http://www.cbat.eps.harvard.edu/iau/cbet/005600/CBET5685_Fig1.png.
The sky-plane configuration diagram showing the observed occultation chords, 
together with the Fresnel diffraction model for the main body, and of the 
apparent satellite, is posted at the following website URL:
http://www.cbat.eps.harvard.edu/iau/cbet/005600/CBET5685_Fig2.png.
     D. Herald and D. Gault, Trans-Tasman Occultation Alliance; and C. Weber,
European Section of IOTA, 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 May 4                       (CBET 5685)              Daniel W. E. Green