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On 12 December 2023, the star $\alpha$ Orionis (Betelgeuse) will be occultedby the asteroid (319) Leona. This represents an extraordinary and uniqueopportunity to analyze the diameter and brightness distribution of Betelgeuse'sphotosphere with extreme angular resolution by studying the light curve as theasteroid occults the star from different points on Earth and at differentwavelengths. Here we present observations of another occultation by Leona on 13September 2023 to determine its projected shape and size in preparation for theDecember 12th event. The occultation observation campaign was highlysuccessful. The effective diameter in projected area derived from the positivedetections at 17 sites turned out to be 66 km $\pm$ 2 km using an ellipticalfit to the instantaneous limb. The body is highly elongated, with dimensions of79.6 $\pm$ 2.2 km x 54.8 $\pm$ 1.3 km in its long and short axis, respectively,at the occultation time. Also, an accurate position coming from theoccultation, to improve the orbit determination of Leona for December 12 isprovided.

The stellar occultation by (319) Leona on 13 September 2023 in preparation for the occultation of Betelgeuse