Electronic Telegram No. 5589
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


(108968) 2001 PE_40
     C. Weber, European Section of the International Occultation Timing
Association (IOTA), Berlin, reports the discovery of an apparent satellite of
the minor planet (108968) based on an occultation of the star UCAC4 427-071562
(which has catalogued magnitudes G = 13.1 and R = 12.0) on 2025 July 12.958
UT.  The magnitude then of this main-belt asteroid was 19.5.  The observations
were made by J. Kaeser and J. Schenker, observing from Schafmatt Observatory
in Aarau, Switzerland, using a 45-cm telescope, and M. Gutekunst, observing
from Eberfing, Germany, using a 28-cm telescope.  All observations were made
with Swiss DVTI+CAM video cameras designed for use by occultation observers
and utilizing Sony IMX430 CMOS sensors.  All of the observers recorded two
consecutive light drops, of durations 1.10 and 0.21 s at Aarau, and 1.14 and
0.09 s at Eberfing, with corresponding chord lengths of 12.5 and 2.4 km
(Aarau) and 12.1 and 1.0 km (Eberfing).  The light drops reached a depth
greater than the G magnitudes of two faint comparison stars (UCAC4 427-071537,
G = 14.1; UCAC4 427-071545, G = 15.4) with the limiting magnitude of the
recordings being about G = 15.8 (Aarau) and 15.5 (Eberfing).  The light
curves were modeled on the basis of Fresnel diffraction; the light curves,
together with corresponding plots of overlaying modeled and observed
light curves, have been posted at the following website URL:
http://www.cbat.eps.harvard.edu/iau/cbet/005500/CBET5589_Fig1.png;
with chords labeled "1+2" being from Eberfing, and chords "4+5" from Aarau.
The red curves in the lower two graphs are from the model, which 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, are posted at the following website URL:
http://www.cbat.eps.harvard.edu/iau/cbet/005500/CBET5589_Fig2.png.  In the
diffraction model (top image), the brightness is represented in gray-scale
with the gray background representing the normal light level of the star and
black representing no light; the shade of gray otherwise represents the
brightness above and below the normal light level at that location.  Inside
each ellipse is a thin red line that represents the physical size of the body.
For the main body, the Fresnel modeling indicated that the observed chords
were generally normal to the limb, and the ellipse fitted to those chords
(having the same apparent area as that of the NEOWISE-catalogue diameter for
this asteroid of 9.2 km) has axes of 12.6 and 6.8 km.  For the satellite, the
modeling indicated an ellipse with axes of 2.90 and 1.83 km.  The separation
of the satellite from the main body is 0".0135 in p.a. 85 deg, with a
sky-plane separation of 23.9 km.  D. Herald, Trans-Tasman Occultation Alliance
(TTOA) and IOTA; and D. Gault, TTOA, 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 August 12                   (CBET 5589)              Daniel W. E. Green