Electronic Telegram No. 5511

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)
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Prepared using the Tamkin Foundation Computer Network

(3927) FELICIAPLATT

D. Herald, Murrumbateman, Australia writes on behalf of the International Occultation Timing Association (IOTA) that V. Sempronio, observing near Benson, AZ, USA; K. Getrost, observing near Fort Gaines, GA, USA; and R. Venable, observing near Yemassee, SC, USA, report the discovery of a satellite of minor planet (3927) from two separate occultation observations made 10 days apart.

On 2024 Dec. 22.1119 UT, Sempronio observed (3927) occult the star UCAC4 494-001568 and measured two clear consecutive occultations with durations of 0.184 and 0.530 s, with an interval of 0.318 s, resulting in chord lengths of 1.5 and 4.0 km with a mid-chord separation of 2.8 km:

Light curve for 2024 Dec. 22.1119 UT V. Sempronio observation. Flux is given in analog-to-digital units, or ADU, which is set to zero for the limiting magnitude of the recording).

Both occultation drops were more than 1.6 magnitudes, clearly excluding a double-star hypothesis.

On 2025 Jan. 1.0431, Getrost and Venable observed (3927) occult the star UCAC4 497-001699. Getrost measured two clear consecutive occultations of duration 0.134 and 0.357 s with an interval of 0.251 s:

Venable operated two stations (one unattended) and measured two occultations by the main body only of 0.100 s:

and 0.305 s:

An ellipse of 4.57 km x 3.90 km was fitted to the three chords across the main body, and a chord length of 1.65 km for the satellite with a mid-chord separation of 3.0 km. The position of the satellite relative to the main body for both occultation observations are: 0".0043 in p.a. 74.0 degrees on 2024 Dec. 22.1119, and 0".0042 in p.a. 67.6 degrees on 2025 Jan. 1.0431.

The sky-plane plot for the Dec. 22 event:

shows the star moving from left to right, with red markers on the chords for disappearance and green markers denoting reappearance, and the length of those markers indicating the uncertainty in the time of that event; the scale of the plot is given in both km (at the asteroid) and in milliarcseconds (as viewed from the earth), while the size of the main body is set to the NEOWISE diameter and that of the satellite is set to a circle with a diameter matching the chord length. The horizontal scale of the corresponding light curve of Sempronio gives the offset in seconds from the specified UTC hour + minute.

The sky-plane plot of the Jan. 1 event:

depicts the light curves of Venable (top chord; shorter occultation), Getrost (middle chord), and Venable (unattended station; bottom chord), in which the primary component has an elliptical profile fitted to match the occultation events in the three chords, with formal uncertainties in the axes of that ellipse being about 100 meters; the size of the satellite is set to a circle with a diameter matching the chord length. The "miss" chords on either side exclude the satellite from being of significantly larger diameter.

D. Gault, Trans-Tasman Occultation Alliance (TTOA), and D. Herald (IOTA and TTOA) aided in the analysis of these observations.

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