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Red supergiant stars are surrounded by a circumstellar environment containing gas and dust. It is created as the star loses its mantle via an unknown mass-loss process. Refining our knowledge of the morphology and physics of such environments is critical to understanding the processes that drive this mass loss. This mass loss phenomenon is also a key element to determine the fate of the star, as it directly determines the mass of the supernova progenitor and hence of the remaining compact object. We present the result of our observations of the CO v=0 J=2-1 emission line of the RSG μ Cep with the NOEMA interferometer at the arcsec angular resolution scale (∼ 500 au at the star distance). Using a combination of 3D deprojection and 3D radiative transfer modeling, we show that at least 25% of the mass loss is due to clumps, randomly arranged in space and emitted episodically by the star.

From November 2019 to April 2020, the prototypical red supergiant Betelgeuse experienced an unexpected and historic dimming. This event was observed worldwide by astrophysicists, and also by the general public with the naked eye. I will present the results of our observing campaign with ESO's VLT and VLTI in the visible and near infrared domains. The observations with SPHERE-ZIMPOL, SPHERE-IRDIS and GRAVITY provide spatially resolved diagnostics of this event. Using PHOENIX atmosphere models and RADMC3D dust radiative transfer simulations, we built a consistent model reproducing the images and the photometry.

From November 2019 to April 2020, the prototypical red supergiant Betelgeuse experienced an unexpected and historic dimming. This event was observed worldwide by astrophysicists, and also by the general public with the naked eye. I will present the results of our observing campaign with ESO's VLT and VLTI in the visible and near infrared domains. The observations with SPHERE-ZIMPOL, SPHERE-IRDIS and GRAVITY provide spatially resolved diagnostics of this event. Using PHOENIX atmosphere models and RADMC3D dust radiative transfer simulations, we built a consistent model reproducing the images and the photometry., {"references":["Refereed publication: Montargès et al. 2021, https://doi.org/10.1038/s41586-021-03546-8"]}

Betelgeuse's recent dimming event is just one of many intriguing phenomena displayed by this exquisite exemplar of red supergiants. In this invited review I will discuss what is known and thought about variability of red supergiants. This will focus on variations on dynamical and thermal timescales, such as convection, pulsation, and possible eruptions shortly before core collapse or mantle depletion; as well as hydrodynamic, electro-magnetic, and chemo-thermal instabilities from the photosphere out through the wind. The aim is to arrive at a holistic picture of how and why red supergiants vary and shed mass, making their own contribution to the entropy increase of the Universe

Since more than a decade, we are monitoring Betelgeuse with our robotic spectroscopic facility STELLA/SES in Teide observatory, Tenerife along with its automated photoelectric telescope T7 in Fairborn observatory, Az. Additionally, we were awarded with exclusive two-band photometric data on Betelgeuse from the BRITE satellite consortium, covering the last seven seasons. In this talk I want to show that the recent dimming event falls together with a re-strengthening of two main excitation periods around 420d and 320d, visible in both, rv data as well as photometric data. These two periods are not prominently visible in the entire data set, but appeared 4-5 years ago, then almost fade for an entire year and reappear in even greater strength 2 years ago.

Detailed monitoring of atmospheres of red supergiant stars is essential for the verification of physical models of mass loss. For such observations it is fundamentally important to employ methods resolving inhomogeneous stellar atmosphere. We present the observations of Betelgeuse using differential speckle polarimetry at the 2.5-m telescope of Caucasian Mountain Observatory of SAI MSU covering the period of 2019-2020 minimum. The observations were secured on 17 dates at wavelengths 465, 550, 625 and 880 nm. A circumstellar reflection nebula with the characteristic angular size of 0.1" was detected for all the dates and at all wavelengths. The morphology of the nebula changed significantly over the observational period. Net polarized brightness of the envelope remained constant until February 2020, while the stellar V band flux decreased 2.5 times. Starting from mid-February 2020, polarized flux of the envelope rose 2.1 times, at the same time the star returned to the pre-minimum state of October 2019., {"references":["Associated publication: arXiv:2005.05215"]}

Betelgeuse, the nearest red supergiant star to Earth, underwent an unusually deep minimum at optical wavelengths during its 2019-2020 pulsation cycle. This kicked off a media frenzy, capturing public as well as professional interest. A number of observing campaigns began covering a large part of the EM spectrum. The (sub)millimetre window, while highly sensitive to cold dust, is also perfectly placed to peer through the circumstellar and interstellar dust to provide an unextinguished view of the star. We present the results of an ongoing (sub)millimetre monitoring campaign including observations taken by the James Clerk Maxwell Telescope, Atacama Pathfinder Experiment, Submillimeter Array and Northern Extended Millimetre Array over a time span of 14 years. We find that Betelgeuse dimmed by ∼20% at these longer wavelengths during the 2020 optical minimum. Using radiative-transfer models, we show that this is likely due to changes in the photosphere (luminosity), possibly a result of convection-driven temperature inhomogeneities; cool spots covering >50% of the star can reproduce the observed behaviour. Temperature changes required to produce the sub-mm dimming also change the optical magnitude by the same amount seen in the V-band and optical spectroscopy (e.g. Levesque & Massey 2020), consistent with TiO photometry and infrared spectroscopy (Harper et al., 2020 a,b)., {"references":["Refereed publication : Dharmawardena et al. 2020, https://doi.org/10.3847/2041-8213/ab9ca6"]}

Although the mass loss of massive stars is of prime importance for their evolution, it is still not well understood. Stellar modelling relies on wind prescriptions that are implemented in 1D evolution codes, but many uncertainties remain. In any case, stellar models cannot follow mass loss burst episodes, like the one that Betelgeuse has undergone last winter. They rely on averaged mass-loss rates, but is there such a thing, from an observational point of view? Can we check wether the winds prescriptions are correct or not? How modifying the mass-loss rates during the RSG phase changes the endpoint of massive stars evolution? I will review our current understanding on these questions from the theoretical point of view.

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., {"references":["Refereed publication, Gupta et al. 2020, https://doi.org/10.1093/mnrasl/slaa101"]}

It is currently an open question in stellar astrophysics which physical processes initiate the mass loss of red supergiants (RSGs). Observations of Betelgeuse during its recent great dimming event in 2019/2020 suggested a discrete highly localised mass ejection event near the stellar surface, a process that may also explain the mass-loss history of RSGs in general. Resolved images of stellar surfaces and close dust formation zones are needed to further investigate such connections between localized photospheric events and the mass loss process. While AO-assisted instrumets enable us to obtain such images for the very few apparently largest stars such as Betelgeuse, long-baseline interferometric imaging is needed to investigate a larger sample of cool evolved stars with smaller apparent radii. Here, we present recent images of the stellar surface of the RSG V602 Car obtained with the PIONIER instrument at the VLTI, and comparisons to latest 3D radiative hydrodynamical (RHD) simulations. They show that 3D RHD simulations reproduce observed features in term of morphology and contrast, but do not explain the observed atmospheric extension. We also present PIONIER and first thermal-infrared VLTI-MATISSE images of the red supergaint AH Scorpii. The MATISSE observations provide images in the L band with a spectral resolution of 506, focusing on the SiO (2-0) bandhead, as well as in the N band focusing on the silicate dust. This allows us to trace the mass-loss process from the stellar surface to the molecular layers, and to the depletion of gas into dust. We also provide an outlook on comparing the levitation of the atmospheres and the dust consendation sequence between RSG and AGB stars.

ALMA has allowed us to study the ejecta around evolved stars with unprecedented resolution. This extremely high resolution at the millimeter domain provides a unique tool to study the processes taking place in the innermost regions of these evolved stars. In particular, the processes leading to the mass ejections of the Red Supergiant stars are unknown. Therefore, studying the characteristics of the mass ejections near the photosphere of the massive stars is essential to constrain the processes leading to the observed gas ejection. In this sense, we have obtained interferometric maps in the range 231.7 – 235.3 GHz of the ejecta around the Red Supergiant star VY CMa with an spatial resolution of ~0.02". These maps revealed a level of complexity higher than anticipated from previous observations. The complexity seems to be due both to structural and chemical processes. The molecular lines covered within these maps range from upper energies 19 up to 3400 K, tracing different excitation conditions. We will present a global view of the different structures observed.

We conduct a rigorous examination of the nearby red supergiant Betelgeuse by drawing on the synthesis of new observational data and three different modeling techniques. Our observational results include the release of new, processed photometric measurements collected with the space-based SMEI instrument prior to Betelgeuse's recent, unprecedented dimming event. We detect the first radial overtone in the photometric data and report a period of $185\pm13.5$ d. Our theoretical predictions include self-consistent results from multi-timescale evolutionary, oscillatory, and hydrodynamic simulations conducted with the Modules for Experiments in Stellar Astrophysics (MESA) software suite. Significant outcomes of our modeling efforts include a precise prediction for the star's radius: $764^{+116}_{-62} R_{\odot}$. In concert with additional constraints, this allows us to derive a new, independent distance estimate of $168^ {+27}_{-15}$ pc and a parallax of $\pi=5.95^{+0.58}_{-0.85}$ mas, in good agreement with Hipparcos but less so with recent radio measurements. Seismic results from both perturbed hydrostatic and evolving hydrodynamic simulations constrain the period and driving mechanisms of Betelgeuse's dominant periodicities in new ways. Our analyses converge to the conclusion that Betelgeuse's $\approx 400$ day period is the result of pulsation in the fundamental mode, driven by the $\kappa$-mechanism. Grid-based hydrodynamic modeling reveals that the behavior of the oscillating envelope is mass-dependent, and likewise suggests that the non-linear pulsation excitation time could serve as a mass constraint. Our results place $\alpha$ Ori definitively in the core helium-burning phase near the base of the red supergiant branch. We report a present-day mass of $16.5$--$19 ~M_{\odot}$---slightly lower than typical literature values., Comment: v5: published in the Astrophysical Journal v3/v4: first revision with the Astrophysical Journal (v4: abstract corrected). v1/v2: submitted version and minor updates. Photometry available at https://konkoly.hu/staff/lmolnar/data/alpha_Ori_SMEI_1d-avg_native-plus-Vmag.txt