The occultation of Betelgeuse by Leona: recovering the stellar surface brightness of a red supergiant, with a diffuse telescope, on Dec 12 1:12 UT

ATel #16374; Sigismondi Costantino (ICRA Rome/ICRANet Pescara, Italy), Claudio Costa (IOTA/ES, Italy), Alfonso Noschese (AstroCampania, Italy)
on 9 Dec 2023; 09:59 UT
Credential Certification: Costantino Sigismondi (sigismondi@icra.it)

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This unique event will occur on December 12, around 1:12 UT, along about a 180 km-wide path, where the eclipse will be partial, and on 18 km of centrality. The asteoroid 319 Leona is 54x80 km (41x60 milliarcseconds), while Betelgeuse is about 48 milliarcseconds wide. For details, observational hints and useful links please read http://www.icra.it/gerbertus/2023/Gerb-19-2023-Sigismondi-Betelgeuse-361-366.pdf It is the first time that an asteroidal occultation offers the possibility to observe the light from various sectors of the stellar surface, owing to the large angular diameter of Betelgeuse, which is the closest red supergiant. The exposed area of Betelgeuse, from each observing location, will determine the light recorded during the partial phases of the occultation. Many observers on the path will realize the "diffuse telescope", as a choral action coordinated by IOTA International Occultation Timing Association US and Europe Sections, with local associations (like AstroCampania and Sabadell). From the penumbral path, the occultation will be visible to the naked eye and recordable with a smartphone (fixed mount), but to recover the tiniest phases of the partial occultation, where the informations of the stellar surface are included, it is necessary to travel to the penumbral path, with a telescope of good size (20 to 30 cm), even if the star is too bright and saturates the detectors. To avoid saturation, but also scintillation, a many-holes mask has been created, in cardboard, in front of the objective telescope, and it has been experimented with 28 cm Schmidt-Cassegrain (SC). Otherwise the stellar signal is strongly hampered by the atmospheric turbulence, with cm-scales, loosing under scintillation all the scientific information. Defocusing the image with the largest telescopes and the mask, has been also tested positively. The visual magnitude of Betelgeuse has been estimated 0.18 on December 8 2023, and it is near the maximum luminosity ATel#9503, ATel#15240, ATel#16001, ATel#13601 of this variable star of SRC-type, with 1.2 yr and 5.9 yr periods. This occultation will permit to verify the hypotesis of reflecting clouds located behind the star, enhancing the total light coming to us from Betelgeuse. Four years ago (Dec 2019 ATel#13341 and Aug 2020 ATel#13982) Betelgeuse underwent a great dimming because of two dust clouds expelled along our line-of-sight. All observations will be credited.

The signal of Betelgeuse with many-holes mask of 4cm-holes at a 28 cm-SC, compared with the one obtained with 10 cm-refractor. The scintillation is greatly reduced with the mask on the largest telescope, without saturating the signal.