Electronic Telegram No. 5582
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


(67426) 2000 QA_98
     M. Nelson, International Occultation Timing Association (IOTA), reports
the discovery of a satellite of minor planet (67426) based on the occultation
of the star UCAC4 542-021447 (Gaia catalogue magnitudes G = 12.9 and R = 12.0)
on 2024 Oct. 28.3625 UT.  This main-belt asteroid was 7.9 mag fainter than the
star, with a NEOWISE-catalogued diameter of 3.4 +/- 0.2 km.  The observation
was done at Charlottesville, VA, USA, using a 28-cm telescope (+ QHY5III-200MM
camera with GPS-linked timing).  The observation indicated two consecutive
occultations of 0.36 and 1.316 s, corresponding to chord lengths of 1.1 and
4.0 km, respectively, with the light curve exhibiting characteristics of
Fresnel diffraction.  The light curve from the observation, together with a
plot of overlaying modeled and observed light curves, is posted at website
URL http://www.cbat.eps.harvard.edu/iau/cbet/005500/CBET5582_Fig1.png.  The
red curve is that from the model; the model was generated for white light, and
the vertical scale of the plot is normalized to a full-light level of 1.0.
The vertical blue dashed lines indicate the location of the physical edges of
the two bodies.  The diffraction model that gave the best agreement to the
observed light curve, and the sky-plane plot of the events, is posted at URL
http://www.cbat.eps.harvard.edu/iau/cbet/005500/CBET5582_Fig2.png.  In the
Fresnel model, the gray background represents the normal brightness of the
star, with the variations in color between white and black representing the
light intensity at those locations; the red lines represent the location of
the physical boundaries of the bodies within that diffraction pattern.  The
observed light curve for the satellite exhibits a central rise consistent
with an Arago/Poisson spot.  The height of that spot, the overall depth of the
drop, and the width of that drop, is consistent with a body having axes of
about 820 x 600 m, with the height of the central rise indicating that the
occultation chord passed within about 40 m of the center of that body.  The
sky-plane plot of the event shows the star "moving" from right to left, with
the main body represented as an ellipse with axes 3.95 x 3.00 km.  The minor
axis is ill-defined by the observation and has been set such that the mean
diameter of that ellipse corresponds to the NEOWISE diameter, supra.  The
diffraction model indicates the center of that ellipse was located about 0.2
km to one side of the occultation chord, with that value being poorly
determined.  The separation of the satellite is 0".0035 in p.a. 253 +/- 4 deg,
with a sky-plane separation of 4.86 km.  D. Herald and D. Gault (Trans-Tasman
Occultation Alliance) aided in the analysis, using a Fresnel diffraction
modeling tool by Bob Anderson (IOTA).


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

                         (C) Copyright 2025 CBAT
2025 July 18                     (CBET 5582)              Daniel W. E. Green