On December 12, 2023, asteroid 319 Leona will occult Betelgeuse along a very thin band that will pass north of the Mediterranean.
This occultation will be exceptional: Leona and Betelgeuse will have almost the same apparent size (~ 50 mas visible). The phenomenon will look more like an (annular) eclipse than a standard occultation.
During Leona’s entry and exit from the Betelgeuse disk (which will last only a few seconds), it will be possible to obtain informations on the distribution of convective cells on the surface of the star. Why doing such observations since we can obtain an image of the surface of the star by interferometry at the VLTI? The VLTI only observes in infrared (between 1 and 13 µm).
Obtaining light curves in visible light (ideally R, G and B bands, or even in a narrow filter Ha), will make it possible to compare the distribution of light on the surface of the star with an infrared observation.
This result will be unprecedented since there is no visible light interferometer allowing such an observation to be made. Note, for the experiment to work, it will be imperative to determine the shape of Leona, and for this to also carefully observe the occultations of other stars by Leona, in particular: September 13, October 29, December 30 and 31, 2023.
It will therefore be necessary to obtain photometric observations with exposure times of a few tens of milliseconds. With Betelgeuse near magnitude 0, this seems feasible, but it is not possible to predict exactly how bright Betelgeuse will be in the heart of the occultation.
In addition, it will be necessary to coordinate the observers to distribute the observations according to different filters.
To go further, it will also be interesting to obtain visible spectrometry to see if the width of the atomic lines changes during the occultation, which would reveal the velocity distribution of the convective cells on the surface of the star.