Images of Betelgeuse with VLTI/MATISSE across the Great Dimming

From Nov. 2019 to May 2020, the red supergiant star Betelgeuse experienced an unprecedented drop of brightness in the visible domain called the Great Dimming event (GDE). Large atmospheric dust clouds and large photospheric convective features are suspected to be responsible for it. To better understand the dimming event, we used mid-infrared long-baseline spectro-interferometric measurements of Betelgeuse taken with the Very Large Telescope Interferometer/Multi AperTure mid-Infrared SpectroScopic Experiment (VLTI/MATISSE) instrument before (Dec. 2018), during (Feb. 2020), and after (Dec. 2020) the GDE. We present data in the 3.98-4.15 µm range to cover SiO spectral features molecules as well as adjacent continuum. We have employed geometrical models, image reconstruction, as well as radiative transfer models to monitor the spatial distribution of SiO over the stellar surface. We find a strongly inhomogeneous spatial distribution of SiO that appears to be looking very different between our observing epochs, indicative of a vigorous activity in the stellar atmosphere. The contrast of our images is small in the pseudo-continuum for all epochs, implying that our MATISSE observations support both cold spot and dust cloud model

Locating dust and molecules in the inner circumstellar environment of R Sculptoris with MATISSE

Stars and planetary system

The extended atmosphere and circumstellar environment of the cool evolved star VX Sagittarii as seen by MATISSE

Stars and planetary system

First MATISSE L-band observations of HD 179218: is the inner 10 au region rich in carbon dust particles?

Stars and planetary system

VLTI-MATISSE L- and N-band aperture-synthesis imaging of the unclassified B[e] star FS Canis Majoris

Stars and planetary system

MATISSE, the VLTI mid-infrared imaging spectro-interferometer

GalaxiesStars and planetary systemsInstrumentatio

Copepods induce paralytic shellfish toxin production in marine dinoflagellates

Among the thousands of unicellular phytoplankton species described in the sea, some frequently occurring and bloom-forming marine dinoflagellates are known to produce the potent neurotoxins causing paralytic shellfish poisoning. The natural function of these toxins is not clear, although they have been hypothesized to act as a chemical defence towards grazers. Here, we show that waterborne cues from the copepod Acartia tonsa induce paralytic shellfish toxin (PST) production in the harmful algal bloom-forming dinoflagellate Alexandrium minutum. Induced A. minutum contained up to 2.5 times more toxins than controls and was more resistant to further copepod grazing. Ingestion of non-toxic alternative prey was not affected by the presence of induced A. minutum. The ability of A. minutum to sense and respond to the presence of grazers by increased PST production and increased resistance to grazing may facilitate the formation of harmful algal blooms in the sea

Sediment-Water column coupling and the fate of the spring phytoplankton bloomin loch Linnhe, a Scottish fjordic sea-loch.Sediment processes and sediment - water fluxes

Sediment-water fluxes of oxygen and nutrients before and after the impact of the spring phytoplankton bloom were measured by core incubation experiments. Less than 10 days after the bloom had settled, chlorophyll was found down to a depth of 2 cm in the sediment. This rapid burial was probably due to mixing during resuspension events. There was some increase in oxygen uptake by the sediment after settlement of the bloom and a concomitant increase in the apparent oxygen diffusion coefficient; this latter increase may indicate a stimulation of bio-irrigation. There was a nitrate influx after settlement of the bloom, but no measurable efflux of ammonium or phosphate from the sediment. There was no increase of sulphate reduction activity after the impact of the bloom nor was solid-phase extractable manganese used as an alternative terminal electron acceptor for oxidation of carbon. We conclude that much of the readily biodegradable organic components of the bloom was mineralized in the water column during sediment resuspension events.<br/