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Author(s): M. Montargès [sup.1] [sup.2] , E. Cannon [sup.2] , E. Lagadec [sup.3] , A. de Koter [sup.2] [sup.4] , P. Kervella [sup.1] , J. Sanchez-Bermudez [sup.5] [sup.6] , C. [...], Red supergiants are the most common final evolutionary stage of stars that have initial masses between 8 and 35 times that of the Sun.sup.1. During this stage, which lasts roughly 100,000 years.sup.1, red supergiants experience substantial mass loss. However, the mechanism for this mass loss is unknown.sup.2. Mass loss may affect the evolutionary path, collapse and future supernova light curve.sup.3 of a red supergiant, and its ultimate fate as either a neutron star or a black hole.sup.4. From November 2019 to March 2020, Betelgeuse--the second-closest red supergiant to Earth (roughly 220 parsecs, or 724 light years, away).sup.5,6--experienced a historic dimming of its visible brightness. Usually having an apparent magnitude between 0.1 and 1.0, its visual brightness decreased to 1.614 [plus or minus] 0.008 magnitudes around 7-13 February 2020.sup.7--an event referred to as Betelgeuse's Great Dimming. Here we report high-angular-resolution observations showing that the southern hemisphere of Betelgeuse was ten times darker than usual in the visible spectrum during its Great Dimming. Observations and modelling support a scenario in which a dust clump formed recently in the vicinity of the star, owing to a local temperature decrease in a cool patch that appeared on the photosphere. The directly imaged brightness variations of Betelgeuse evolved on a timescale of weeks. Our findings suggest that a component of mass loss from red supergiants.sup.8 is inhomogeneous, linked to a very contrasted and rapidly changing photosphere. The southern hemisphere of Betelgeuse during its Great Dimming was an order of magnitude darker than usual, owing to a cool patch on the photosphere and associated dust formation.

Author(s): R. Garcia Lopez [sup.1] [sup.1] [sup.2] [sup.3] , A. Natta [sup.2] , A. Caratti o Garatti [sup.1] [sup.2] [sup.3] , T. P. Ray [sup.2] , R. Fedriani [sup.2] [sup.4] [...], Stars form by accreting material from their surrounding disks. There is a consensus that matter flowing through the disk is channelled onto the stellar surface by the stellar magnetic field. This is thought to be strong enough to truncate the disk close to the corotation radius, at which the disk rotates at the same rate as the star. Spectro-interferometric studies in young stellar objects show that hydrogen emission (a well known tracer of accretion activity) mostly comes from a region a few milliarcseconds across, usually located within the dust sublimation radius.sup.1-3. The origin of the hydrogen emission could be the stellar magnetosphere, a rotating wind or a disk. In the case of intermediate-mass Herbig AeBe stars, the fact that Brackett [gamma] (Br[gamma]) emission is spatially resolved rules out the possibility that most of the emission comes from the magnetosphere.sup.4-6 because the weak magnetic fields (some tenths of a gauss) detected in these sources.sup.7,8 result in very compact magnetospheres. In the case of T Tauri sources, their larger magnetospheres should make them easier to resolve. The small angular size of the magnetosphere (a few tenths of a milliarcsecond), however, along with the presence of winds.sup.9,10 make the interpretation of the observations challenging. Here we report optical long-baseline interferometric observations that spatially resolve the inner disk of the T Tauri star TW Hydrae. We find that the near-infrared hydrogen emission comes from a region approximately 3.5 stellar radii across. This region is within the continuum dusty disk emitting region (7 stellar radii across) and also within the corotation radius, which is twice as big. This indicates that the hydrogen emission originates in the accretion columns (funnel flows of matter accreting onto the star), as expected in magnetospheric accretion models, rather than in a wind emitted at much larger distance (more than one astronomical unit). The size of the inner disk of the T Tauri star TW Hydrae is determined using optical long-baseline interferometric observations, indicating that hydrogen emission comes from a region approximately 3.5 stellar radii across.