Electronic Telegram No. 5686
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


(92590) 2000 PT_13
     P. Maley, International Occultation Timing Association (IOTA) and NASA
Johnson Space Center Astronomical Society, reports the discovery of an 
apparent satellite of minor planet (92590) based on an occultation of the star 
UCAC4 557-036088 (which has catalogued Gaia magnitudes G = 13.13 and R = 
12.46) on 2026 Mar. 7.279 UT.  The magnitude of (92590) was 19.66 (6.5 
magnitudes fainter than the target star).  Maley observed from Carefree, AZ, 
USA, using a 28-cm telescope (+ Watec WAT-910HX video camera + and Open VTI 
GPS time inserter).  The recording showed two consecutive occultations of 
durations 0.55 and 0.64 s, separated by 0.46 s, corresponding to chord lengths 
of 1.2 and 3.0 km.  The flux during for the first occultation dropped to the 
limiting magnitude of the recording (approximately G = 15.4 and R = 14.8), and 
the flux for the second event dropped to that of comparison star UCAC4 
556-036487 (Gaia magnitudes G = 14.1 and R = 13.7).  The depths of these drops 
(2.3 and 1.0 magnitudes in G; 2.3 and 1.2 magnitudes in R) exclude a double 
star being the explanation for the light curve.  The Gaia DR3 magnitude 
measurements for this main-belt asteroid indicate a rotational light curve 
variation of at least 0.4 magnitude, indicating that the asteroid has a 
moderate oblateness.  Ryan et al. (2015, A.Ap. 578, A42) provide diameters 
from ATLAS data of 2.8, 3.1, and 3.4 km for the thermal-modeling beaming 
parameter (eta; cf. Myhrvold 2018, Icarus 303, 91) of 0.80, 1.07, and 1.34 
(respectively).  The main body was modeled to fit the observed light curve 
using the larger diameter of 3.4 km, with the fitted model having axes of 4.6 
x 2.5 km.  The satellite was modeled as a spherical body with a diameter of 
1.2 km.  The separation of the satellite was 0".0041 in p.a. 112 +/- 14 
degrees, with a sky-plane separation of 4.85 km.  L. Liberato (GaiaMoons, 
Observatoire de la Cote d'Azur) advises that an analysis of Gaia astrometry 
supports the existence of a satellite having an orbital period of 39.58 +/- 
9.44 hr.  Further, given the size ratio of the bodies derived from the 
occultation, the orbital separation is between 10 and 40 km, and possibly as 
large as 60 km.  The observed and modeled light curves are posted at website
URL http://www.cbat.eps.harvard.edu/iau/cbet/005600/CBET5686_Fig1.png.  The 
sky-plane configuration diagram showing the observed occultation chords, 
together with the Fresnel diffraction model for the main body and satellite, 
is posted at the following website URL:
http://www.cbat.eps.harvard.edu/iau/cbet/005600/CBET5686_Fig2.png.
     D. Herald and D. Gault, Trans-Tasman Occultation Alliance; and C. Weber,
European Section of the IOTA, aided in the analysis.  GaiaMoons is a project 
funded by the Agence Nationale de la Recherche (France).


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

                         (C) Copyright 2026 CBAT
2026 May 6                       (CBET 5686)              Daniel W. E. Green