Thermodynamical condensation calculations of the dust grains in the out-flowing winds of the dimming Betelgeuse

Betelgeuse (\(\alpha\) Orionis) is one of the brightest and magnificent stars in the sky owing to its closeness to our solar system. Because it is one of the brightest red supergiant (RSG) stars, it has always been a well observed target to deduce several features such as luminosity, effective temperature, and the evolutionary phases of RSGs. Betelgeuse underwent an unprecedented reduction in its brightness during the period October 2019 to March 2020. This dimming episode made this magnificent star even more attractive. The reduction was estimated to be ~40 per cent of its usual brightness, leading to a speculation that the star is in its last evolutionary stage(s), and it is soon going to explode. However, further observations ruled out this possibility of explosion and the exact reason of this dimming is still an open problem. In the debate of reason of reduction in brightness, either the dust condensation in our line of sight, or the cooling of large portion of the photosphere are considered as the possible explanations for this event. In the present work, we made an attempt to understand the dust condensation sequence and its mass distribution in the vicinity of Betelgeuse. We performed the detailed thermodynamical condensation calculations in the outflowing winds of the Betelgeuse. The calculations include the distinct dust-gas equilibrium as well as non-equilibrium scenarios of dust grain condensation around its cooling envelope. The condensation calculations have provided the nature of dust that could condense in the stellar winds. The dust grains are essentially found to be oxides of Al, Ca, Ti, silicates of Al, Ca, Mg and Fe metal. In addition, we have determined the normalized mass of the dust grains of various compositions that could be present around the star and causing the reduction in its brightness. The dust mass is predicted to be \(\le\)~0.5 per cent of the total gas mass in the localized region of the star falling in our line of sight, if equilibrium prevails. The maximum dust mass is predicted to be in olivine for the silicates and metallic form for iron. The results of this work got published in Monthly Notices of Royal Astronomical Society Letters