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

TL;DR

This paper reports an occultation observation of asteroid (319) Leona on 13 September 2023, determining its shape and size to aid future observations of Betelgeuse's upcoming occultation, with implications for stellar diameter analysis.

Contribution

It provides the first detailed shape and size measurements of Leona from an occultation, improving orbit data ahead of the Betelgeuse event.

Findings

Leona's effective diameter is 66 km from occultation data.

Leona is highly elongated, measuring approximately 80 km by 55 km.

The observation improves Leona's orbit accuracy for December 2023.

Abstract

On 12 December 2023, the star $\alpha$ Orionis (Betelgeuse) will be occulted by the asteroid (319) Leona. This represents an extraordinary and unique opportunity to analyze the diameter and brightness distribution of Betelgeuse's photosphere with extreme angular resolution by studying the light curve as the asteroid occults the star from different points on Earth and at different wavelengths. Here we present observations of another occultation by Leona on 13 September 2023 to determine its projected shape and size in preparation for the December 12th event. The occultation observation campaign was highly successful. The effective diameter in projected area derived from the positive detections at 17 sites turned out to be 66 km $\pm$ 2 km using an elliptical fit to the instantaneous limb. The body is highly elongated, with dimensions of 79.6 $\pm$ 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 the occultation, to improve the orbit determination of Leona for December 12 is provided.