Electronic Telegram No. 5691
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


(3619) NASH
     L. Benedyktowicz, Polish Amateur Astronomers' Society; and D. Blazewicz, 
International Occultation Timing Association (IOTA), European Section, report 
the discovery of an apparent satellite of minor planet (3619) based on an 
occultation of the star UCAC4 371-077463 (which has catalogued Gaia magnitudes 
G = 12.03 and R = 11.27), as observed on 2026 Apr. 28.96 UT.  This main-belt 
asteroid was 5.8 magnitudes fainter than the star.  Benedyktowicz observed 
from Widoma, Poland, using a 20-cm Schmidt-Cassegrain telescope (+ ASI432MM 
CMOS video system and a Shelyak TimeBox that synchronizes computer time with 
GPS time) and recorded two consecutive occultations of duration 0.26 and 0.66 
s, corresponding to chord lengths of 1.6 and 3.9 km, respectively, with the 
interval between the chords being 1.12 s, corresponding to 6.7 km.  In the 
recording, the flux of both drops was lower than that of the comparison star, 
UCAC4 371-077422, which has magnitudes of 13.7 (G) and 13.0 (R), ruling out a 
double star as an explanation.  The limiting magnitudes of the recording were 
approximately G = 14.3 and R = 13.5.  Blazewicz observed from Klaj, Poland, 
using a 35-cm Dobsonian telescope (+ GPS-disciplined DVTI + CAM 430 CMOS video 
system) and recorded an occultation of 0.48 s, corresponding to a chord length 
of 2.9 km.  The flux dropped below that of the comparison star (UCAC4 
371-077422; Gaia magnitudes G = 13.7 and R = 13.0), ruling out a double-star 
scenario.  The approximate limiting magnitudes were G = 14.2 and R = 13.4.
     No diameter measurements from infrared satellites or rotation lightcurves 
are known for the asteroid (3619).  The asteroid's profile was derived using 
an elliptical fit, measuring 4.49 × 3.76 km with a position angle of 98.0 
degrees.  The length of the main axis is consistent with the 4.32-km diameter 
listed in the Asteroid Lightcurve Data Exchange Format (ALCDEF) database 
(Warner et al. 2009) using the absolute magnitude derived by Mahlke et al.
(2021, Icarus 354, 114094).  Assuming that the apparent satellite has a 
circular profile, its diameter is between 1.5 and 2.8 km (i.e., 2.15 +/- 0.65 
km), and its separation from the main body was measured to be 0".0087 in p.a. 
300 (+8/-6) degrees, corresponding to a distance of 9.3 km. 
     The observed lightcurves, together with the curves modelled using the 
Fresnel diffraction model, can be found via the following website URL: 
http://www.cbat.eps.harvard.edu/iau/cbet/005600/CBET5691_Fig1.png.  In 
Blazewicz’s lightcurve, a red arrow indicates the location corresponding to 
the "satellite event" in Benedyktowicz’s recording.  The sky-plane plot of 
the system, together with the Fresnel models for the minimum and maximum size 
of the apparent satellite, is posted at the following website URL: 
http://www.cbat.eps.harvard.edu/iau/cbet/005600/CBET5691_Fig2.png. 
     D. Herald and D. Gault, Trans-Tasman Occultation Alliance; and C. Weber, 
European Section of the 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 26                      (CBET 5691)              Daniel W. E. Green